Sports Biomechanics: Reducing Injury and Improving Performance
Sports Biomechanics: Reducing Injury and Improving Performance
Sport Science Research Institute, Sheffield Hallam University, UK
E & FN SPON
An Imprint of Routledge
London and New York
First published 1999 by E & FN Spon, an imprint of Routledge 11 New Fetter Lane, London EC4P 4EE This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” Simultaneously published in the USA and Canada by Routledge 29 West 35th Street, New York, NY 10001 © 1999 Roger Bartlett All rights reserved. No part of this book may be reprinted or reproduced or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data Bartlett, Roger. Sports biomechanics: preventing injury and improving performance /Roger Bartlett. p. cm. Includes bibliographical references and index. ISBN 0-419-18440-6 1. Sports—Physiological aspects. 2. Human mechanics. 3. Sports injuries—Prevention. I. Title. RC1235.B37 1998 612′.044–dc21 98–21961 CIP ISBN 0-203-47456-2 Master e-book ISBN
ISBN 0-203-78280-1 (Adobe eReader Format) ISBN 0 419 18440 6 (Print Edition)
To Mel. Mum and my late Father .
1 Structure and composition 1.2 Maximum force and muscle activation 1. anisotropy and viscoelasticity 1.4 Warm-up 1.3.4 Bone 1.5.2 Elastic modulus and related properties 1.8 Non-homogeneity.1 Muscle elasticity and contractility 1.2 Bone: loading and biomechanical properties 1.1 Causes of injury 1.6.3 Mechanical stiffness 1.3.10 Exercises xiii xv 1 1 3 3 5 6 6 11 12 13 14 14 14 15 17 17 17 18 20 20 20 21 21 22 22 23 24 27 27 27 28 30 31 31 .3.4.6 Creep 1.Contents Preface Permissions Part One Biomechanics of Sports Injury Introduction 1 Causes of injury and the properties of materials 1.3.9 Stress concentration 1.1 Structure and composition 1.6.2 Age and sex 1.5 Hardness 1.3 Plasticity and strain energy 18.104.22.168 Biological and other materials 1.1 Immobilisation and disuse 1.7 Fatigue failure 1.3 Exercise and training 1.8.3 Response of a material to load 1.5.6 Muscle properties and behaviour 22.214.171.124 Stress and strain 1.8.5 Cartilage 1.4 Toughness and crack prevention 1.7 Ligament and tendon properties 126.96.36.199 The stretch-shortening cycle 1.2 Biomechanical properties 1.9 Summary 188.8.131.52.6.8 Factors affecting properties of biological tissue 1.
7 Summary 60 2.6 Fitness and training status and injury 58 2.1 Musculoskeletal injury: some useful definitions 65 3 The effects of sports equipment and technique on injury 67 3.1 Sports surfaces 67 3.5 The elbow 51 2.11 References 32 1.1 The pelvis and the hip joint 45 2.1 Introduction 76 3.3 Joint and soft tissue injuries 42 2.3 Other sports and exercise equipment and injury 87 .4.2.3 Muscle-tendon unit 43 2.10 Further reading 64 Appendix 2.1.viii Contents 1.3 The structure of a running shoe 77 3.2 Characteristics of sports surfaces 68 3.2.4 The wrist and hand 50 2.4 Sports injuries to joints and associated tissues 45 2. back and neck 53 2.4 Biomechanical assessment of surfaces 71 3. age and growth 56 2.5.5 Injury aspects of sports surfaces 74 3.12 Further reading 35 2 Injuries in sport: how the body behaves under load 36 2.4 Footwear and injury 81 3.2.2 Footwear: biomechanics and injury aspects 76 184.108.40.206.6 Running shoes and rearfoot control 85 3.1 Introduction 36 220.127.116.11 Bone properties 41 2.1 Introduction 67 3.4.7 The head.1 Sex.1.3 Specific sports surfaces 70 3.2 Bone injuries 37 2.4.5 Impact and the running shoe 82 3.1.8 Exercises 61 2.2 Magnitude of load 40 2.4.1 Articular cartilage 42 18.104.22.168 The knee 45 2.2 Bony alignment 57 2.2 Ligaments 42 2.3 The ankle and foot 49 2.1.2 Biomechanical requirements of a running shoe 77 3.3 Load rate 40 2.1 Type of fracture 37 22.214.171.124.9 References 61 126.96.36.199.6 The shoulder 53 2.5 Genetic factors in sports injury 56 2.2.4.
3 The lower extremity 90 188.8.131.52 Concluding comments 138 4.3 The upper extremity 93 3.Contents 3.1 Solving the indeterminacy (or redundancy) problem 124 4.4.7 Joint reaction forces and moments in multiplesegment systems 122 4.1 The head and neck 88 3.5 An example of the estimation of a load causing traumatic injury 135 4.7 Exercises 138 4.3.2 The head and trunk 92 3.3 Determination of muscle forces from inverse dynamics 124 4.2.1 Introduction 109 4.1 Static joint and muscle forces for a single segment with one muscle 110 4.4 Musculoskeletal injury—technique aspects 91 3.2.6 Exercises 99 3.2.2 The upper extremity 89 3.3 Assumptions underlying the above models 115 4.1 Patellar ligament rupture 135 4.2.2 Inverse optimisation 125 4.1 Introduction 91 184.108.40.206 Dynamic joint and muscle forces for a single segment with one muscle 112 220.127.116.11.8 References 141 4.5 Planar joint reaction forces and moments for a single segment 116 4.2 Other surface characteristics 108 4 Calculating the loads 109 4.7 References 100 18.104.22.168.3.3 Use of EMG to estimate muscle force 133 4.8 Further reading 104 Appendix 3.6 Summary 138 4.6 Planar joint reaction forces and moments for segment chains 119 4.4 Determination of ligament and bone forces 134 22.214.171.124 Summary 99 3.4 Alpine skiing: release bindings 91 3.4 Forces acting on a body segment with more than one muscle—the indeterminacy problem 116 4.4 The lower extremity 97 3.9 Further reading 144 ix .1 Artificial surfaces 105 Appendix 3.3.2 Forces acting on a body segment in two dimensions 110 4.
4 Concluding comments 161 5.6 Summary 174 5.2 Principles of partial generality 155 5.3.3 Conclusions—future trends 195 6.3 Statistical modelling 181 6.4.2 Structural analysis of movement 152 5.5.5 Summary 196 6.1.2 Optimisation 192 6.5.4 Hierarchical model of a vertical jump 186 6.3.1 Types of statistical model 181 6.2 Limitations of statistical modelling 183 6.1 Principles of coordinated movement 149 5.2 Biomechanical principles of coordinated movement 153 5.4 Mathematical modelling 189 6.4 Kinesiological analysis of sports movements 162 5.3.1 An approach to kinesiological analysis 162 5.1 Phase analysis of ballistic movements 157 5.7 References 198 6.4.x Contents Part Two Biomechanical Improvement of Sports Performance 147 Introduction 147 5 Aspects of biomechanical analysis of sports performance 149 5.5 Some limitations to kinesiological analysis 168 5.3 The analysis chart 166 5.3.9 Further reading 177 6 Biomechanical optimisation of sports techniques 178 6.4.1 What muscles really do 168 5.2.1 Simulation 190 6.4.8 Further reading 200 7 Mathematical models of sports motions 201 7.6 Exercises 196 6.1 How is movement controlled? 150 5.3 Temporal and phase analysis 156 5.3.4 Examples 168 126.96.36.199.2 A formalised kinesiological analysis procedure 163 5.3.3 Theory-based statistical modelling 184 6.4.3 Phase analysis of other activities 160 5.2 Phase analysis of running 159 5.3.2 The trial and error approach 179 6.2 Open and closed kinetic chains 173 5.1 Introduction 178 6.4.1 Introduction 201 .1 Universal principles 154 5.4.8 References 176 5.7 Exercises 174 5.
3.3 Parallel representations 8.6 Computer simulation models 8.5 Simulation evaluation 7.3.2 Technique assessment models and their limitations in feedback 8.1 The importance of feedback 8.4 A more comprehensive model of skeletal muscle 188.8.131.52 Hanavan’s human body model 184.108.40.206 Live demonstrations 8.4 Hatze’s anthropometric model 7.4 Sensitivity analysis 220.127.116.11 Optimisation 18.104.22.168 The thrower model 22.214.171.124 The role of technique training 7.2.6 Summary 7.2.4 More complex models of the sports performer 126.96.36.199 Simulation evaluation 7.2 202 202 204 205 205 209 210 210 211 213 218 220 220 220 221 223 226 228 231 231 231 231 232 234 236 239 239 240 241 242 244 244 247 248 248 248 249 250 251 251 252 254 xi .5 Models of skeletal muscle 7.3 Muscle models 7.2.4 Textbook technique 8.2 The computed torque approach 7.1 Introduction 7.9 Further reading 8 Feedback of results to improve performance 8.2 Linked segment models of aerial movement 7.7 Exercises 7.5 Evaluation and uses of Hatze’s model of skeletal muscle 7.2 Simulation 7.5 Graphical (diagrammatic) models 8. optimisation and sensitivity analysis 7.2.1 Introduction 7.2.2 Serial recordings 8.3.6 Conclusions 7.5 Concluding comments 7.7 Analysis charts 8.6 Concluding comments 7.1 The javelin flight model 7.3.3 Simple models of the sports performer 188.8.131.52.2.5.Contents Optimal javelin release 7.1 Introduction 184.108.40.206 References 7.8 Concluding comments 220.127.116.11 Simulation.5 Yeadon’s mathematical inertia model of the human body 7.
8 18.104.22.168.6 8.xii Contents 8.9 Author index Subject index .2 The uses of computer simulation and optimisation in feedback 261 Summary 262 Exercises 262 References 263 Further reading 265 267 271 8.7 8.4 8.1 Learning or relearning a technique 255 8.1 Overview 260 8.2 How to plan technique training 257 Information feedback and motor learning 258 Use of computer-based feedback 260 8.5 8.3.
so that the non-mathematical reader should find most of the material easily accessible. then these have been included. I should like to acknowledge the contributions of several colleagues at my former university. The book could not have been produced without the support of the Head of the Department of Exercise and Sport Science. It also considers aspects of the behaviour of sports implements. I would single out for particular thanks Russell Best. were invaluable. this one focuses on third year undergraduate and postgraduate topics. to those intending to become physical education teachers. and of Vasilios Baltzopoulos. The book is organised into two parts. Wherever possible. on Chapters 1 to 4. and to all those interested in sports performance and injury. Whereas that text mostly covered first and second year undergraduate material. The mathematical element in biomechanics often deters students without a mathematical background. Where I consider that basic mathematical equations add to the clarity of the material. on all of the chapters of the book. This book is intended as the companion volume to Introduction to Sports Biomechanics. It is a scientific discipline that is relevant to all students of the exercise and sport sciences. in particular. It is concerned. Neither would it have been possible without the inspiration provided by my many undergraduate and postgraduate students over the years. The detailed and carefully considered comments of Carl Payton.Preface Sports biomechanics uses the scientific methods of mechanics to study the effects of various forces on the sports performer. particularly in Chapter 4. Thanks are also due to Dunstan Orchard and Tim Bowen for their help with many of the illustrations and advice on various aspects of the software packages used to produce the illustrations. Les Burwitz. However. which deal respectively with the two key issues of sports biomechanics: why injuries occur and how performance can be improved. footwear and surfaces where these affect performance or injury. The production of any textbook relies on the cooperation of many people other than the author. with the ways in which sports movements are performed—often referred to as sports techniques. and the tolerance of Julie Lovatt. I have otherwise avoided extensive mathematical development of the topics. Manchester Metropolitan. these topics are approached from a practical sport viewpoint. Of this latter group. who gently goaded me .
my deepest gratitude once again to my dearest Melanie.xiv Preface into writing this book and its predecessor. and by no means least. Roger Bartlett September 1998 . I am also grateful to those publishers and authors who allowed me to reproduce their illustrations. without whose encouragement and example I would never have started on this book or its predecessor. Last.
3 (September). 85–89. F. Atha.R. from Nigg. with minor adaptations. (1989) Modern technique analysis sheet for the horizontal jumps: Part 1—The Long Jump. .5 reprinted. Figure 6. with permission from Elsevier Science. New Studies in Athletics. and Hales. USA. with kind permission from the IAAF. (1991) Biomechanical estimate of output force of ligamentum patellae in case of its rupture during jerk. 23. Figure 4. 27(2). (1986) Biomechanics of Running Shoes.8 reprinted from Yeadon. with kind permission from the author. 47–62. Figure 8. Acta Unwersitatis Carolinae Gymnica. (1990) The simulation of aerial movement—I. 59–66. The determination of orientation angles from film data. Journal of Biomechanics. Monaco. M. Journal of Biomechanics. 17 rue Princesse Florestine. G.R. 23.M.D. Figure 7.11 reprinted from Yeadon. Champaign. with kind permission from the author. M. K. with permission from Elsevier Science. (1990) The simulation of aerial movement—IV. BP359-MC98007. J. Cedex. IL.. 71–82. A computer simulation model. B.Permissions Figure 3. Human Kinetics.15 reprinted from Jelen.6 reprinted from Tidow.
contractility. Where necessary. are considered. The chapter concludes with an outline of the ways in which various factors—immobilisation. cartilage. The former may involve a sequence of stages that begins with a description of the incidence and types of sports injury. age and sex. The composition and biomechanical properties of bone. muscle activation. Chapter 2 covers the biomechanical reasons why injuries occur in sport. This relates to the properties of biological materials (Chapter 1). The final stage in the prevention sequence relates to measures to reduce the injury risk. The sports injuries that affect the Introduction . the mechanisms of injury occurrence (Chapter 2) and the estimation of forces in biological structures (Chapter 4). and exercise—affect the properties of biological tissue. the load and tissue characteristics involved in injury are considered along with the terminology used to describe injuries to the human musculoskeletal system. The next stage is to identify the factors and mechanisms that affect the occurrence of sports injury. and their behaviour under various forms of loading. The most important mechanical properties of biological and non-biological sports materials are covered. the generation of maximal force in a muscle.Part One Biomechanics of Sports Injury Sports biomechanics has often been described as having two aims that may be incompatible: the reduction of injury and the improvement of performance. In Chapter 1. although extensive mathematical development of the topics covered has been avoided. and how these depend on the load characteristics. ligaments and the muscle-tendon unit. Viscoelasticity and its significance for biological materials is explained. Some of the most important ones from a biomechanical point of view are considered in Chapter 3. including cartilage. ligament and tendon. An understanding is provided of the various injuries that occur to bone and soft tissues. basic mathematical equations have been introduced. and the distinction between overuse and traumatic injury is made clear. Muscle elasticity. muscle stiffness and the importance of the stretch-shortening cycle are all described.
In Chapter 4 the difficulties of calculating the forces in muscles and ligaments are considered. is also covered. Finally a rare example of muscle force calculations from a cine film recording of an activity where an injury occurred is considered. including typical simplifications made in inverse dynamics modelling. fitness and training factors have on injury are considered. The influence of footwear on injury in sport and exercise. even when this information is available. A glossary of possibly unfamiliar terminology is provided at the end of this chapter. The various approaches to overcoming the redundancy (or indeterminacy) problem are described. the effects that genetic. are also covered. including the structure of a running shoe and the contribution of its various parts to achieving the biomechanical requirements of the shoe. along with how the procedures can be extended to multi-link systems. The method of inverse optimisation is covered. The chapter concludes by providing an understanding of the effects of technique on the occurrence of musculoskeletal injury in a variety of sports and exercises. The methods used to assess sports surfaces biomechanically and the injury aspects of sports surfaces are covered. and attention is given to an evaluation of the various cost functions used. .2 Part One: Biomechanics of Sports Injury major joints of the lower and upper extremities. are highlighted. The limitations that exist. Such surfaces are often designed with ‘performance enhancement’ as the primary aim rather than injury reduction. Attention is given to the injury moderating role of other sport and exercise protective equipment. Chapter 3 includes a consideration of the important characteristics of a sports surface and how specific sports surfaces behave. The biomechanical requirements of a running shoe are considered. and the back and neck. The uses and limitations of EMG in estimating muscle force are outlined. with particular reference to impact absorption and rearfoot control. Finally. The equations for planar force and moment calculations from inverse dynamics for single segments and for a segment chain are explained.
Injury can be defined as follows: Injury occurs when the load applied to a tissue exceeds its failure tolerance. muscle activation. Sports injuries are. for the purpose of this book. Injuries 1. in contrast to individual sports (van Mechelen. age and sex.1 Causes of injury .Causes of injury and the properties of materials 1 This chapter provides a background to the biomechanical reasons why injuries occur and an understanding of the properties of materials. considered to be any injury resulting from participation in sport or exercise that causes either a reduction in that activity or a need for medical advice or treatment. the generation of maximal force in a muscle. steroids and exercise—affect the properties of biological tissue. After reading this chapter you should be able to: • list the biomechanical reasons why injuries occur in sport • define the load and tissue characteristics involved in injury • define and explain the mechanical properties of non-biological materials that are important for sports injury • explain viscoelasticity and its significance for biological materials • describe the composition and biomechanical properties of bone and its behaviour under various forms of loading • understand the composition and biomechanical properties of cartilage. including some of the factors that can modify the behaviour of biological materials. ligament and tendon • explain muscle elasticity. muscle stiffness and the importance of the stretch-shortening cycle • describe how various factors—immobilisation. Competing at a high standard increases the incidence of sports injuries. 1993). contractility. which are also more likely during the growth spurt in adolescence. in team sports more injuries occur in matches than in training. moderately serious (eight to 21 days) or serious (21 or more days or permanent damage). Not surprisingly. Sports injuries are often classified in terms of the activity time lost: minor (one to seven days). contact sports have a greater injury risk than non-contact ones.
1993a with Moffroid. Technique • Faulty technique imposing excessive loads on the performer. Nigg. It is also instructive to consider the underlying reasons why injuries occur in sport. • Illegal technique. imposing an excessive . including alignment abnormalities. Magnitude of load.g.4 Causes of injury/properties of materials are relatively common in many sports (see. Fitness or training status • • Lack of flexibility or joint laxity. or imbalance in. lack of. Structural properties of bones and joints. These can be considered as factors intrinsic or extrinsic to the performer. Frequency of load repetition. fatigue and other training errors. 1993). Age (for example. Load rate. However. The following provides a useful and focused biomechanical subdivision. Characteristics of loaded tissues • • Material properties of bones and soft tissues. Chapter 4 will consider some problems involved in calculating the loads in the human musculoskeletal system during sport and exercise. incorrect body weight. young or old athletes) or sex. authors sometimes differ in interpreting training and technique aspects to be intrinsic or extrinsic (e. 1982). muscular strength. such as pes planus (flat feet). for example. and leg length discrepancies. 1993). Load characteristics • • • • Type of load. including overtraining. Excessive training load for current fitness status. such as high tackling in rugby. Genetic factors • • Innate musculoskeletal deformities. each of which will be considered in this chapter or in Chapter 2. The occurrence and types of injuries to the musculoskeletal system in sport and exercise depend on the following (adapted from Gozna. compare Kannus.
Below a temperature known as the ‘glass transition temperature’ many polymers lose their rubbery (or plastic) behaviour and behave like glass. are built up from long chain-like molecules with a carbon backbone. Equipment and surfaces • • Human-surface interface including surface quality. 1. For example. The following sections consider important aspects of materials in general and specific properties of biological tissues. Fibre-reinforced polymers are now the most common form of composite. but also how other materials can affect injury and how they can best be used in sport and exercise. for example. It is important to understand not only how biological materials fail. Other equipment design features. That is. footwear-surface interaction. equipment and surfaces on sports injuries is considered in Chapter 3. Fibre-reinforced composites are relatively recent and even more important sports materials. or glassreinforced plastic. The incidence of injury may be reduced or increased by. Polymers. usually called plastics. 1993).or glass fibre-reinforced polymers exploit the high strength (the ability to withstand loads without breaking) of carbon or glass fibres and the toughness (resistance to cracking on impact) of polymers (Easterling. The influence of technique.2 Biological and other materials All injuries in sport and exercise involve failure of a biological material. of course. or the performer. The introduction of new materials into the design and manufacture of sports equipment has also.6 respectively. . muscles. had important consequences for sports performance. vaulting pole that replaced the earlier metal pole and totally transformed this athletic event. foot-footwear (shoe or boot) interaction. 5 The first two of these are considered in sections 2. in which the materials are combined to use the beneficial properties of each component (fibres and polymers). shoes for sport and exercise. Thus carbon.5 and 2. The most commonly quoted example is the fibreglass. The most important non-biological materials in the context of this book are polymers and fibre-reinforced composites.Biological and other materials load on the opponent. cartilage. This change from plastic to brittle behaviour at the glass transition temperature is characteristic of many materials. polymers are important materials in sport. sports surfaces and protective equipment. ligaments and tendons. a rubber ball cooled in liquid nitrogen will shatter if dropped. through performer-opponent impacts or prolonged contacts. fascia. it is necessary to know the loads and properties that cause specific tissues to fail. To understand how injury to the musculoskeletal system occurs. These relate to the material and structural properties of the various tissues of the musculoskeletal system—cortical and cancellous bone. they become brittle owing to closer bonding of chains.
The shear stress (τ) and strain (v) are calculated differently from normal stresses and strains: τ=F/A where A is the area over which (not perpendicular to which) the shear force acts and v is the angular deformation of the material in radians. 1992). The deformation of the material that is produced is usually represented as the strain (ε) defined as e= r/r. compression resistance. An applied force (F) produces a deformation (strain) and a restoring stress in the deformed bonds. These are.3 Response of a material to load 1. In compression. bone is often subject to compression whereas most soft tissues have little. The third basic type of stress is shear (Figure 1.1c). The strain is often expressed as a percentage and is non-dimensional. damping. The material properties that are important in this context are known as bulk mechanical properties. ultimate tensile strength. Two of the three basic types of stress are of this form: tension (Figure 1. to understand the behaviour of a material under various loads.1b). In the International System of Units (SI). a knowledge of both the way the load affects the material and the properties of the material is necessary. by bone.1a) and compression (Figure 1. yield strength. Stress (σ) is a measure of a material’s ability to resist an applied force. When a material is loaded. fracture resistance or toughness. where r is the change in a specific dimension of the material.g. 1. the unit of stress is the pascal (Pa): 1Pa=1N·m-2. Because the bonds have been deformed. if any. it is defined as σ=F/A. with an original value of r. they try to restore themselves to their original positions. 1993). as a simple form of loading. where F is the force acting on the material and A is the area of an appropriate crosssectional plane for the type of stress. hardness. The stresses and strains in a material are known as the normal stresses and strains when they are defined perpendicular to the relevant cross-section of the material (Biewener. In tension. thermal fatigue. the stress acts in the direction of the applied force and the strain is positive as the material lengthens. for materials in general: density.1c). This arises when a force (the shear force) acts on a plane parallel to the surface of the material.6 Causes of injury/properties of materials As noted above. it undergoes deformation because the atomic bonds bend. or the angle of shear (Figure 1. the stress is again in the direction of the applied force but the strain is negative as the length of the material decreases. tension is experienced by most soft tissues in the body but not.1 STRESS AND STRAIN The term ‘load’ will be used in this book to mean the sum of all the forces and moments acting on the body or a specific tissue structure (e.3. and creep strength. stretch or compress. thus generating a stress in the material. . fatigue strength. Nigg. elastic modulus.
(c) shear.1 Basic types of stress and strain: (a) tension.Response of a material to load 7 Figure 1. . (b) compression.
this moment Figure 1. An axis somewhere between the two surfaces (it will be midway for a uniform rectangular cross-section) experiences no deformation and hence no stress. they are more commonly experienced in conjunction with bending or torsion (twisting). normal and shear stresses will then act (Figure 1. for example a diving board of rectangular cross-section (Figure 1. 1991 for further consideration of three-dimensional stresses).2a).3b). y. 1992).2b). both the shape of the loaded structure and its material properties affect its ability to withstand loads (Biewener.3a). Although tension and compressive stresses can occur alone. (b) principal stresses and strains. The stresses (σ) caused by bending are sometimes called ‘bending stresses’. from the neutral axis (Figure 1. This is known as the ‘neutral axis’. These stresses resist the ‘bending moment’ (M) applied to them. These are called the ‘principal stresses’ (Figure 1.3b).2a) can be ‘cut’ in such a way that the stresses on all its six sides will be normal. In such combined forms of loading. . however. The stress at any section of the beam increases with the distance. The upper surface of the beam is in tension as the material is stretched whereas the lower surface is compressed. Bending can be illustrated in terms of a cantilever beam. loaded only by the weight (F) of the diver. the stresses and strains developed in the tissues of the body. At any location in the material. It should be noted that an element of material (Figure 1.2 Three-dimensional stresses in a material: (a) normal and shear stresses.8 Causes of injury/properties of materials For most loads experienced in sport. or in the materials making up sports equipment. that is a beam fixed at one end. they are axial— either tensile (σt) or compressive (σc) (Figure 1. are usually three-dimensional (see Özkaya and Nordin.
(d) transverse second moment of area. For such a beam. the bending moment at any section (e. (c) bending moment diagram.3c).3c).Response of a material to load generally varies along the beam.3 Bending of a beam: (a) cantilever beam of rectangular cross-section. increasing from zero (at F) to FL at the base of the beam (Figure 1. Here y is the distance from the neutral axis and It is the second moment of 9 Figure 1. xx) is equal to the force applied to the beam (F) multiplied by the distance of its point of application from that section (x). The stress can then be expressed as σ=My/It. . (b) stress diagram. as for the example of a cantilever beam (Figure 1.g.
T is the applied torque about the neutral axis and Ip is the polar second moment of area. the second moment of area multiplied by the density of the material. the hollow circular cylinder is optimal. It can be considered as similar to bending but with the maximum stresses being shear stresses. Torsional loading causes shear stresses in the material and results Figure 1. for unit length of beam. Bones. In both tension and bending. for example. In structures designed to resist only one type of loading in one direction. This second moment of area is sometimes known as the ‘area moment of inertia’.1).4 Torsion: (a) shear stress increases with radius. This provides reasonable values of both the transverse and polar moments of inertia (see Table 1. (b) principal stresses (at 45° to long axis of cylinder).1. The strongest structure for resisting combined bending and torsion is the circular cylinder. . The polar second moment of area is closely related to the polar moment of inertia and is measured about the longitudinal axis of the cylinder. Both the transverse moment of inertia (bending resistance) and the polar moment of inertia (torsional resistance) are important. The principal stresses—the normal compression and tension stresses— act at 45° to the long axis of the cylinder (Figure 1. the shear stress increases with radius (Figure 1. as in the vertical beam of Table 1.10 Causes of injury/properties of materials area of the beam’s cross-section about the transverse axis that intersects the neutral axis (see Figure 1. providing good load resistance and minimising mass. Biological tissues are often subject to combined loading from various directions. the moment of inertia is the second moment of mass. in the axes of principal stress being considerably different from the principal axes of inertia. the resistance to that type and direction of loading can be maximised.3d. where r is the radial distance from the neutral axis. Torsion or ‘twisting’ is a common form of loading for biological tissues. which is. the resistance to an applied load depends on the moment of inertia of the loaded structure. The shear stress caused by torsion is given by: τ=Tr/Ip.4b). For a circular rod. to maximise the strength-to-weight ratio.4a). are required to resist bending and torsional loads in sport. where It=bh3/12).
3. within the elastic range.2 ELASTIC MODULUS AND RELATED PROPERTIES The elastic modulus expresses the resistance of a material to deformation. its stiffness.Response of a material to load Table 1.1 Relative resistances to bending and torsional loads 11 1. in which stress is linearly related to strain .
which represents an energy loss or hysteresis loop. force–extension curve. Many biological materials.7). as in a trampoline bed. • It should be noted that E and G are only defined for elastic deformation. that is the difference between the original and final areas divided by the original area. the elastic modulus is related to the glass transition temperature. because the material has entered the region of plastic deformation. Some of this energy will be recoverable elastic strain energy (lightly shaded in Figure 1. protective equipment. show far greater ranges of linear stress-strain behaviour (see section 1. such as tendons. vaulting pole. Non-biological materials that are elastic tend to be so only for small strains. the shear modulus (G) is the ratio of shear stress (τ) to shear strain (v). and the reduction of cross-sectional area. The area under the force–extension curve up to any chosen strain is a measure of energy known as strain energy. such as vaulting poles. 1. or compressed ball. The ductility of a material is often expressed by: the elongation. not all materials behave elastically even for small strains. shoe sole. • For tension or compression the modulus of elasticity (E) is defined as the ratio of tensile or compressive stress (σ) to tensile or compressive strain (ε). that part of the deformation that was elastic is recovered. large deformations may be desirable for impact or for applications where strain energy is absorbed. Strain energy is stored in any deformed material during deformation. for which removal of the load results in the object regaining its original dimensions. Figure 1. Ductility is rarely defined for biological materials and is normally expressed as a percentage. For polymers. as in a vaulting . This is the maximal tensile force before failure (the ultimate tensile strength) divided by the original cross-sectional area.3 PLASTICITY AND STRAIN ENERGY If a material is strained beyond its elastic limit and the load is then removed.5a).g. typically up to 1%. The elastic modulus is the ratio of the stress to the strain in that region for a particular load type. Elastic strain energy is useful when the material serves as a temporary energy store. as in protective equipment. for example plasticine and putty. For shear. and identically shaped.5a) and is equal to the area under the equivalent.3.5a) and some will be lost as plastic strain energy (darkly shaded in Figure 1. However. In sport and exercise activities. a permanent ‘set’ remains. the extension at fracture divided by the original length. The ultimate tensile stress (σTS) is also important.12 Causes of injury/properties of materials (e. Plastic strain energy is useful when the material is required to dampen vibration or absorb energy. However. This energy loss is proportional to the shaded area under the stress-strain curve (Figure 1.5a).
(b) viscoelastic structure (tendon). have low toughness since they have only small plastic deformation before fracture occurs. is a critical combination of stress and crack length. Brittle materials. 1.Response of a material to load pole or trampoline bed. 13 Figure 1. A ductile material is capable of absorbing much more energy before it fractures than a less ductile material is.3.4 TOUGHNESS AND CRACK PREVENTION The toughness of a material is its ability to absorb energy during plastic deformation (it is measured in an impact test). The resistance to this. . Another function of the matrix is to protect the fibres and prevent the formation of minute surface cracks on the fibre surface.5 Stress-strain behaviour of typical materials: (a) non-biological material. known as fracture toughness.g. The matrix material of a composite often helps to prevent crack propagation.5b) for viscoelastic materials (see below). Resilience is a measure of the energy absorbed by a material that is returned when the load is removed. such as glass. Hysteresis relates to differences in the load-deflection curve for loading and unloading and these can be particularly marked (e. Figure 1. It is related to the elastic and plastic behaviour of the material and to its hysteresis characteristics. This type of fracture occurs extremely quickly when enough energy is available to make the crack advance. which lower its strength. Many materials are brittle below their glass transition temperature and fail by the rapid propagation of cracks.
. Creep is commonly observed in viscoelastic materials (see section 1. wear and penetration. The maximum range endured without failure fora mean stress of zero is called fatigue limit.8). time and temperature. at this stress. as fatigue failures of biological tissue (see chapter 2).7 FATIGUE FAILURE The formation and growth of cracks in a material can occur at lower loads than would normally be associated with failure if the load is cycled repetitively. loads that cause no permanent deformation at room temperature can cause the material to creep—a slow continuous deformation with time. The number of stress reversals that will be withstood without failure depends on the range of stress (maximum minus minimum) and the mean stress.5 HARDNESS The hardness of a material (measured by a type of compression test) is a property that largely determines the resistance of the material to scratching. 1. the number of reversals that can be tolerated tends to infinity (Figure 1.3.3. The measured strain is a function of stress.14 Causes of injury/properties of materials 1.6).3.3. It is not frequently used for biological materials. Figure 1. 1.6 CREEP As the temperature of a material is increased. in effect.6 Fitigue behaviour of a material. Many overuse injuries can be considered.
and whether the bone is cancellous or compact. Furthermore. 1982).15). biological materials are anisotropic. For example.5b and 1.3. such that some parts of the material behave differently from others. ANISOTROPY AND VISCOELASTICITY The properties of biological materials are generally far more complex than those of non-biological ones. even in the elastic region (see Figures 1. The properties of biological materials are position-dependent. .Response of a material to load 1.8 NON-HOMOGENEITY. that is their properties depend on the direction in 15 Figure 1. that is they are nonhomogeneous. all affect its properties (Gozna.g. the region of the bone (e. Biological materials are often nonlinear in their stress-strain behaviour.7 Schematic representation of the phenomenon of creep under a constant stress. the lateral compared with the medial cortex). the type of bone.
8 Schematic representation of the phenomenon of stress relaxation under a constant strain. 1991).8). They have a non-linear stress-strain history and are strain-rate sensitive. that is they continue to deform with time (e.7). They also show ‘stress relaxation’ under a constant applied strain.g. Viscoelastic materials ‘creep’ under a constant applied load. a property of all biological tissues (see also Özkaya and Nordin. All viscoelastic . Figure 1. One of the major differences between biological and non-biological materials is viscoelasticity (from viscous and elastic). offering a higher resistance when loaded faster (Chan and Hsu.g. that is the stress decreases with time (e. which they are loaded.16 Causes of injury/properties of materials Figure 1. Figure 1. 1993).
These pack to form the matrix of the bone. Figure 1. Cancellous bone has a cellular or porous structure. The sponginess of cancellous bone helps to absorb energy but gives a lower strength than cortical bone does. 17 1. The trabeculae are more densely packed in those parts of the bone that have to transmit the greatest stress.9 STRESS CONCENTRATION Stress concentration is a term used when high localised stresses result from sudden changes in the shape of the stressed structure.Bone materials have some degree of hysteresis (e. Because of the anisotropy of bone (its properties depend on the direction of loading). In biological tissues. a similar mode of failure occurs in cancellous bone. for example. consist of a periphery of cortical. bone surrounding a core of cancellous bone (trabecular or spongy bone).5b). or compact. where cracks propagate along the length of the bone.1) and minimises the chance of fracture.1 STRUCTURE AND COMPOSITION Many bones. particularly long bones.9).. The overall structure of long bones gives an optimal strength-to-weight ratio. The major structural element of cortical bone is the osteon. a fixation device or callus in a bone (see Gozna. the failure is brittle owing to cracks running across the bone surface.3. The shapes are rod. anisotropic. In the second. These shape changes can be considered as non-uniformities in the internal behaviour of the structure. 1978).3. 1. failure is ductile as osteons and fibres are pulled apart.or platelike. this is an indication of the tissue’s viscous properties (Butler et al. The trabeculae have varying shapes and spatial orientations. In the first of these. A narrower middle section in long bones reduces bending stresses (see section 1.4. The orientation of the trabeculae corresponds to the direction of tensile and compressive stresses and is roughly orthogonal (Figure 1. viscoelastic. stress concentrations arise from. the mechanisms of crack propagation depend on the orientation of the bone: cracks propagate more easily in the transverse than in the longitudinal direction. brittle material which is weakest when loaded in tension. This is made possible by the requirement for greatest stress resistance at the periphery of the bone and by the internal struts which the trabecular system represents.4 Bone . 1. Two fracture mechanisms occur in cortical bone. A local stress concentration that exceeds the breaking stress of the material will lead to crack formation. 1982).g. This permits maximum economy of the structure as expressed by its strength-to-weight ratio. Cortical bone is a non-homogeneous.
however. 1984).18 Causes of injury/properties of materials Figure 1. 1.9 Trabecular pattern of cancellous bone corresponds to the orthogonal pattern of tensile and compressive stresses. These properties also vary with the direction in which the load is applied (anisotropy). It is also viscoelastic. and its properties depend on the strain rate (Bonfield. schematically represented in the inset. experiencing only a small elongation before breaking.2 BONE: LOADING AND BIOMECHANICAL PROPERTIES Bone is relatively inelastic. cortical bone has twice as large an elastic modulus . range of deformation. returning to its original shape over a finite timespan. it is elastic in its normal. the type and region of the bone also affect its mechanical properties. Because of its non-homogeneity. for example. Above a certain load it behaves plastically. or physiological.4.
deformation and energy-to-failure were 183 N·m. Failure loads of 1. At higher rates of loading. its strain-to-failure decreases. 1994) is higher than the values for cancellous bone of 1. 1984). Tension and compression Both the ultimate strength and the elastic modulus are important. A wide range of 7–30 GPa has been reported for the elastic modulus of ‘wet’ compact bone in a longitudinal orientation (Bonfield. bending and torsion Steindler (1973) reported the energy required to cause bending failure to be 24 J for the fibula. that for cancellous bone is lower (van Audekercke and Martens. bending loads lead to failure on the convex (tensile) side of the bone.5 kN for the tibia have been reported under static compression (e. compact bone increases slightly in strength and stiffness. Because of its brittleness. 1989). tibia and fibula (Nigg and Grimston. Its brittleness is due to the mineral content and this makes bone susceptible to shock loads (e.8MPa summarised by van Audekercke and Martens (1984). depending on the bone and its age and preparation.Bone along the long axis as across it (Bonfield. bending and shearing). Van Audekercke and Martens (1984).9 kN for the patella. 1993). 6. The associated ultimate torque. 19 . For a range of femurs and tibias from people aged between 27 and 92 years. 38 J for the ulna and 44 J for the radius. 1982). mean torsional stiffnesses of 562N·m·rad -1 and 326N·m·rad -1 respectively have been reported. and hence stiffness. for cancellous bone in the range 23 MPa to 1. 1984). 1994). as discussed in Chapter 2. most compressive fractures occur under dynamic loading. 7.5 kN for the femur and 4. Compact bone shows a characteristically brittle behaviour at higher load rates. Shearing.0 kN for the humerus. A range of 106–224 MPa for the compressive strength of compact bone (Nigg and Grimston. when less energy is absorbed before it fails (Pope and Beynnon. 1973). summarising the work of several investigators. fracture is not often associated with a pure load but with combined loads (such as compression. These latter values again depended on the bone and its age and preparation. it fails before other biological materials when deformed (Gozna. 110–170 J for the humerus. Nordin and Frankel. 1989).52 GPa. showed much lower values of elastic modulus. Also. The fracture pattern for torsionally loaded bone corresponds to an initial failure in shear through crack propagation (Nordin and Frankel.g. Because the tensile strength of bone is less than its compressive strength. The tensile strength of compact bone has been summarised as being within the range of 80–150 MPa for the femur. Steindler.4–25. In practice.g. 1984). 20° and 35J (femur) and 101 N·m.
Near the bone the collagenous fibres are perpendicular to the bone. 1. Hyaline cartilage consists of between 20% and 40% chondroitin. as the collateral ligaments are relaxed and weight-bearing is no longer likely. cartilage returns to its initial elasticity within a relatively short time providing that the load was . as during gait. Wide variations exist in the reported values of the compressive and tensile properties of bone. Articular cartilage is an avascular substance consisting of cells. In the perpendicular zone.1 STRUCTURE AND COMPOSITION Of all types of connective tissue. In greater degrees of flexion a gliding motion occurs over a reduced contact area. this reduced area is made possible by the reduction of load. 1973). For example. 1. 1973). Normal cartilage has a typical viscoelastic behaviour. but not uniform. elasticity. It has an elastic modulus in tension that decreases with increasing depth from the cartilage surface because of the collagen fibre orientation. this substance has a high sulphuric acid content and contains collagen and a polymer (chondromucoid) of acetylated disaccharide chondrosine. The concentration of chondroitin is lower in the surface zone because of the high content of collagen fibres. The increased area is maintained on initial flexion when weight-bearing is still likely. leading to wear and tear. helping to distribute the joint stress which varies with the amount of contact. in the fully extended knee where probable weight-bearing is combined with ligamentous loading and muscle tension. 1980). Compressibility is about 50–60%. the joint contact area is increased by the menisci. collagen fibres and hyaline substance. fibres weave around the cartilage cells forming chondromes (Steindler.10). The compressive modulus increases with load as the cartilage is compressed and the chondromes resist the load. This is greatest in the direction of joint motion and where the joint pressure is greatest. through adaptation to mechanical stresses (Steindler. The effect of load is to cause a rapid initial deformation followed by a more gradual increase (Figure 1. After the load is removed.2 BIOMECHANICAL PROPERTIES Cartilage has a high.5 Cartilage 1.5..5. The function of joint cartilage is to provide a smooth articular surface.20 Causes of injury/properties of materials 23. articular (joint) cartilage is the most severely exposed to stress.7° and 25J (tibia) (Martens et al. The deformation of cartilage helps to increase the joint contact area and range of motion. The fibres then run through a transition zone before becoming parallel to the surface where an abundance of fibres allows them to move apart with no decrement in tensile strength.
Muscle properties and behaviour 21 Figure 1. 1993). A similar load held for a longer period (Figure 1. the interactions between muscle and tendon. and the collagen . 1.6 Muscle properties and behaviour The most important physical properties of muscle are elasticity and contractility. Prolonged standing causes creep of the partly fibrocartilaginous intervertebral discs. muscle activation and stiffness. will cause more deformation and an increased impairment of elasticity. Its elastic limits are much lower for repeated than for single loading (Nigg. The ultimate compressive stress of cartilage has been reported as 5MPa (in Shrive and Frank.1 MUSCLE ELASTICITY AND CONTRACTILITY Muscle elasticity is due mainly to the sarcolemma and the connective tissue sheath which surrounds the muscle fibres. The only passive stress experienced by muscle is tension. which may cause degeneration. 1.10).6. losing 17 mm of height in the first two hours after rising (Pope and Beynnon. after stretching ceases. this largely explains why people are tallest in the morning. 1993). which results in elongation and a decrease in cross-sectional area. or a greater load.10 Schematic representation of the effects of the duration of loading (continuous line) and unloading (dashed lines) on the deformation of cartilage. 1995). Also important for sports injuries are: the maximum force developed. The elastic fibres in the connective tissue cause shortening. and the phenomena of the stretch-shortening cycle. of short enough duration and low enough magnitude.
where m and ρ are the mass and density of the muscle. A range of values for specific tension have been reported (e.22 Causes of injury/properties of materials fibres protect against overstretching. The effects of training may also be important (see below). The smaller ones are recruited first.6. 1. The modulus of elasticity is not defined. The different values of specific tension cited in the literature may be caused by different fibre composition. 1992). The last two of these are defined when the muscle’s sarcomeres are at the optimal length (2.6. rf is the muscle fibre length and α is the fibre pennation angle (Figure 1.3 MECHANICAL STIFFNESS The mechanical stiffness of a muscle is the instantaneous rate of change of force with length (that is the slope of the muscle tension-length curve). The maximum force depends on the number of cross-bridges attached. 1.8 µm) for tension generation (Pierrynowski. The force per unit physiological cross-sectional area is often known as the ‘specific tension’ of the muscle. The factors affecting a muscle’s ability to produce force include its length. 1995). It should be noted that pcsa=(m cosa)/(rf/ρ). The former is an orderly sequence based on the size of the a-motoneuron. Smaller muscles have fewer motor units and depend more on increasing their stimulation rate. Pierrynowski. If more motor units can be recruited.11). but is independent of the number of cross-bridges operating.g. Contractility refers to the unique ability of muscle to shorten and produce movement.. but muscle can be stretched by up to 60% before rupture. The extent of rate-coding is muscle-dependent. This rises with time during tension and is directly related to the degree of filament . Unstimulated muscles possess low stiffness (or high compliance). 1995). these are typically slow twitch with a low maximum tension and a long contraction time. Muscle activation is regulated through motor unit recruitment and the motor unit stimulation rate (or rate-coding). 1997). velocity. the breaking stress is much less than that of tendon. and the physiological cross-sectional area of the motor unit. their firing (or stimulation) rate and synchrony. physiological cross-sectional area and activation (see also Bartlett. then this dominates. the maximum contraction velocity reflects the maximum rate of cross-bridge turnover. a maximum value of 350 kPa is often used to estimate the maximum muscle force from its physiological crosssectional area (pcsa). determination of pcsa or neural factors (Fukunaga et al. The contractility of muscle is somewhere between 25% and 75% of its resting length. fibre type.2 MAXIMUM FORCE AND MUSCLE ACTIVATION The maximum force developed in each motor unit of a muscle is related to the number of fibres recruited.
The stretch-shortening effect has not been accurately measured or fully explained. 1992). Force enhancement occurs in dynamic concentric contractions after stretch. such that the force-velocity relationship shifts towards increasing forces at any given velocity (Chapman. such as occur in many sports.6.11 Muscle fibre pennation angle (α). the velocity of recoil of the tendon during the shortening phase may be such that the velocity of the muscle fibres is less than that of the muscle-tendon unit. 1989). Zajac.g. Komi. muscle and reflex properties and the central nervous system interact in determining how stiffness affects the control of movement (Gottlieb. The creation of larger muscle forces in.4 THE STRETCH-SHORTENING CYCLE Many muscle contractions in dynamic movements in sport undergo a stretchshortening cycle. It is important not only in research but also in strength and power training for athletic activities. however. 1993). van Ingen Schenau. 1992). The mechanisms thought to be involved are elastic energy storage and release (mostly in tendon). Stiffness is often considered to be under reflex control with regulation through both the length component of the muscle spindle receptors and the force-feedback component of the Golgi tendon organs (Komi. 1992) as do their effects in the stretch-shortening cycle (see below). 1984 with Alexander.g. Furthermore. has been carried out on the effects of blocking of reflex actions. Some evidence shows that muscle fibres may shorten whilst the whole muscle-tendon unit lengthens. Furthermore. 23 1. 1989). Some research. Figure 1.g. 1996).Muscle properties and behaviour overlap and cross-bridge attachment (Gregor.g. 1980). and reflex potentiation (e. mostly on animals. It is clear. The exact role of the various reflex components in stiffness regulation in fast human movements in sport remains to be fully established (e. whether or not they bring the muscle fibres closer to their optimal length and velocity (Huijing. Komi. At high rates of change of force. van Ingen Schenau. These interactions between tendinous structures and muscle fibres may substantially affect elastic and reflex potentiation in the stretchshortening cycle. 1993). 1984). There have been alternative explanations for the phenomenon of the stretch-shortening cycle (e. The result would be a shift to the right of the force-velocity curve of the contractile element (Gregor.13. 1992) and its value in achieving maximal performance (e. Differences of opinion also exist on the amount of elastic energy that can be stored (compare van Ingen Schenau. in which the eccentric phase is considered to enhance performance in the concentric phase (Figure 1. 1984) and increasing the elastic energy stored in tendon (Huijing. for example. a countermovement jump compared with a squat jump is probably important both in terms of the pre-load effect (e.g. muscle is stiff. particularly in eccentric contractions for which stiffness values over 200 times as great as for concentric contractions have been reported (Luhtanen and Komi.12). that the reflexes can almost double the stiffness of the muscles alone at some joints. similar to Figure 1. . 1992).
24 Causes of injury/properties of materials Figure 1. 1. 1993).7 Ligament and tendon properties In general. The linear strain region may be as great as 20–40% . (c) as (b) but with a delay between the two phases (after Komi.12 Force potentiation in the stretch-shortening cycle: (a) concentric (+) knee extension. The effects of this force enhancement on the tension-velocity and tension-length curves of human muscle in vivo has yet to be fully established. not enough information exists on the in vivo characteristics of ligaments (Hawkings. 1985). 1992). The elastic modulus of the anterior longitudinal ligament of the spine is 12. (b) eccentric (–) contraction followed immediately by concentric (+) contraction.3 MPa with an ultimate tensile stress similar to that for tendon (see below).
Ligament and tendon properties 25 Figure 1. 1993). When unstressed. Obviously. The histological make-up of ligaments varies from those having largely elastic fibres. much greater than for tendon (Butler et al. and other biological tissues. vary with species. and failure strains as high as 60%.. As with cartilage (Figure 1. The stiffness of the ligament initially increases with the force applied to it. collagen fibres are recruited from the crimped state to become straightened. to cord-like thickenings of collagen. which increases resistance and stabilises the joint. such as the ligamentum flavum. which are arranged into fibres. ligaments offer early and increasing resistance to tensile loading over a narrow range of joint motion. This crimped pattern is crucial for normal joint mobility as it allows a limited range of almost unresisted movement. the duration of the stress is important.14). Ligaments can return to their pre-stretched length when the load is removed and they . the mechanical properties of ligaments. If displaced towards the outer limit of movement. In addition. donor history and age. and testing procedures. closed circles—squat jump (after Gregor. The tropocollagen molecules are organised into cross-striated fibrils. 1989). 1978).13 Schematic representation of the stretch-shortening effect on the forcevelocity relationship in a vertical jump: open circles—countermovement jump. the fibres have a crimped pattern owing to cross-linking of collagen fibres with elastic and reticular ones. Because of their non-linear tensile properties (Figure 1.10). ligament mechanoreceptors may contribute to maintenance of joint integrity by initiating the recruitment of muscles as dynamic stabilisers (Grabiner.
Collagen is a regular triple helix with cross-links. such as walking and jogging.14 Stress-strain (or load-extension) behaviour of ligament loaded in tension: 1) toe region. The stiffness is smaller for low loads as the collagen crimping pattern causes a less steep gradient of the load–extension and stress–strain curves in the toe region (Figure 1. . 3) failure region.14). the value is within the band of 45–125 MPa reported by Woo (1986) for human tendon.14). The value of between 49 MPa and 98 MPa for mammalian tendon cited in Curwin and Stanish (1984) is less than the value of 120 MPa reported by them for the Achilles tendon in fast running. having a large collagen content. reversible region up to 4% strain. giving a material and associated structures of great tensile strength that resists stretching if the fibres are correctly aligned. Strenuous activities are normally in the early part of the linear region (Hawkings. Daily activities. stiffness nearly constant. are usually in the toe of the stress–strain curve (Figure 1. 1993). However.26 Causes of injury/properties of materials behave viscoelastically. no consensus exists on the ultimate tensile stress of human tendon. having an elastic modulus of 800 MPa–2GPa. This discrepancy was attributed by them to the strain-rate-dependent properties of tendon. and the ultimate Figure 1. 1993). Tendon is a relatively stiff material. The toe region extends to about 3% strain. The ratedependent behaviour of ligaments may be important in cyclic activities where ligament softening—the decrease in the peak ligament force with successive cycles—may occur. Tendons are strong. however. assuming a cross-sectional area of 75mm2. Tendon tissue is similar to that of fascia. 2) almost linear region. The implications of this for sports performance are not yet known (Hawkings. with the linear.
this represents a limited viscoelastic behaviour for a biological material (Herzog and Loitz. the loss of mass is about 1–2% annually for women and 0. females reach a peak bone mass that is about 30% less than that for males (Kannus.8. Because of this.8. Bone atrophy occurs.2 AGE AND SEX Total bone mass and bone density increase during adolescence. 1993). Some disagreement exists about whether bone mass peaks at a particular age or simply reaches a plateau starting from an age of 20–25 years and ending at 35–40. 1993b). 1992). with the mass and size of the bone decreasing through the loss of equal proportions of bone matrix and mineral content (Booth and Gould. In general. 1995). and it takes longer to regain than to lose tissue strength (Hawkings. Animal experiments have shown a 52% reduction of the ultimate stress of the tibia-medial collateral ligament-femur complex after nine weeks and 62% after 12 weeks immobilisation (Loitz and Frank. having a relative hysteresis of only 2. the change in muscle fibre length will be small compared to the length change of the whole muscle– tendon unit. The loss of cortical bone density . Immobilisation of bone weakens the cortex and thereby affects the strength of the ligament–bone junction.Factors affecting properties of biological tissue (failure) strain around 8–10% (Herzog and Loitz. 1993). immobilisation has resulted in decreases in the strength of the medial collateral ligament of around 30% in a 9–12 week period. 1995). The effects of immobilisation on bone are generally the opposite to the beneficial effects of exercise (see below).5–1% for men (Zetterberg. 27 1. Immobilisation of ligaments causes a reduction in both their failure strength and the energy absorption before failure.1 IMMOBILISATION AND DISUSE Collagen fibres are adversely affected by inactivity and favourably influenced by chronic physical activity.8 Factors affecting properties of biological tissue 1. Within the physiological range. It should be noted that the energy storage is likely to be limited unless the tendon is subject to large forces. Beyond that age.5–20%. When the tendon compliance is high. in both the rate of development and the final mass and density. The compliance (elasticity) of tendon is important in how tendon interacts with the contraction of muscle tissue. As well as having a relatively high tensile strength and stiffness. 1. 1975). This leads to an increase in joint stiffness and injury susceptibility. In animal experiments. Significant individual age and sex variations occur. as in the eccentric phase of the stretch-shortening cycle (Huijing. tendon is often considered the major site within the muscle-tendon unit for the storage of elastic energy. 1993). tendon is resilient.
intermittent pressure leads to the formation of spurs and bridges (arthritis) to compensate for deterioration of cartilage. The decrease in stiffness and the lower failure load with ageing for ligaments. owing to fewer cross-links. The mechanical properties of collagenous tissue show increases in ultimate stress and elastic modulus during growth. although there are few conclusive laboratory and clinical studies to show that these do prevent injury (Best and Garrett. this explains the increased frequency of avulsion fractures in the young. 1993b). may be linked to a decrease in physical activity. and tensile forces caused by muscle action. Until this time. and 12% for energy absorption to failure (from Nigg and Grimston. for example. this is more marked in females than in males. good physical fitness is also considered crucial to avoiding sports injury. 1993a). 1993). Regular exercise may retard the decline with ageing by as much as 50% (Hawkings. create an electrical potential which induces bone growth. The loss of strength is a combination of the bones becoming thinner and an increasing number of calcified osteons leading to brittleness (Edington and Edgerton. Attention needs to be paid not only to the intensity and duration of training. Long distance runners have been reported as having 20% higher bone mineral content than controls. As bones age they experience a decrease in compressive strength and fracture more easily. 1976). occur during further ageing. Continuous excessive pressure on bones causes atrophy.3 EXERCISE AND TRAINING Progressive exercise is thought to improve the mechanical and structural properties of tissues. because of the reduced ultimate strength of tissues for repeated compared with single loading (Nigg. Warm-up and cool-down are also considered to be important features of injury prevention (Kannus. tendon is more resistant to tension than is bone. This may explain why people who are physically active have significantly greater bone densities than those who are less active (Kannus. Degeneration begins early.28 Causes of injury/properties of materials can be as high as 2–3% per year for the first decade after the menopause (Kannus. but also to the repetitions within an exercise period and the rest between periods. 1993). Preventive training includes training of muscle. Frank and Shrive (1995) cited a decrease of 60% in the ultimate tensile stress of the anterior cruciate ligament from young adulthood to the age of 65 years. 1993b).8. and local increases in the bone mineral . Reductions in these properties. 1994). mobility and flexibility. Normal compressive forces. 1993a). The average reductions per decade with age in the 20– 102 year range are 5% and 9% for ultimate tensile stress and strain respectively. with the central artery disappearing from tendons as early as the age of 30. and coordination. 1.
Junction strength changes are related to the type of exercise regimen as well as its duration. with increased stiffness. It has been reported that high intensity training leads to an increase in bone density. 1996). endurance training before trauma may lead to increased junction strength after repair (Booth and Gould. 1975). for example in tennis players (Zetterberg. Booth and Gould. Within its elastic limits. as well as some increase in mass. and this is accompanied by an increased elasticity (Nigg.Factors affecting properties of biological tissue content have been found for loaded areas of the skeleton. an improved recruitment pattern and a change in fibre orientation (Nigg. 1993a). then stiffness can be trained to be 29 . Zernicke (1989) considered that high intensity training (70–80% of maximum oxygen uptake) inhibits bone remodelling and leads to a significant reduction in bending stiffness and energy-to-failure. and the identity and manner of the response of cells initially receptive to that change. 1975). are highly responsive to changes in mechanical loading—they increase in both size and mineralisation and undergo substantial cortical remodelling. in particular. but relatively high intensity training inhibits these (Booth and Gould. The length-feedback component of the muscle spindle response has been claimed to be trainable. 1989). The long bones of the extremities. causing a reduction in specific tension. It has often been reported (e. but that low to moderate intensity training has no such effect. The physiological mechanisms stimulated depend on the specific form of training. for example. (1993). 1993). remain to be fully established. 1993). as this affects the patterns of motor unit activation (Kraemer et al.g. Cyclic bending strain may be a mechanism to account for selective bone remodelling (Zernicke. as through activities such as running and swimming. related to an increase in muscle mass. which has even more effect on the force-time curve than on muscle structure (Komi.. found that 16 weeks of heavy resistance training increased the physiological cross-sectional area by 33% and the pennation angle by 29%. How mechanical change affects remodelling. If these hypotheses are correct. increasing the muscle spindle discharge for the same stretch. 1975) that exercise leads to hypertrophy of ligaments and tendons. Training can increase muscle strength though physiological adaptations. can lead to stress relaxation and a reduction of tissue load. ultimate strength and energy-to-failure. cartilage increases in thickness with short-and long-term exercise. 1993). Kawakami et al. The muscle force-time curve is sensitive to heavy resistance and explosive training. Cyclic loading of such tissues with a fixed displacement. Increased ligamentous laxity after exercise is an example of the creep properties of tissue (Best and Garrett. Connective tissue can experience stress relaxation and creep during exercise. It has also been hypothesised that training can decrease the force-feedback component of the Golgi tendon organs. 1989). Low intensity training promotes increases in bone length and growth in the growing athlete.
without any size increase of the muscle. where the muscle’s failure properties can be altered (Best and Garrett. and at highly stretched lengths.30 Causes of injury/properties of materials Figure 1. 1993b). 1989). The maximum isometric force developed by a muscle changes little with temperature.15 Components of a hypothetical stretch reflex showing how the stretch from the initial to final length affects the muscle tension through: the muscular component. as in Figure 1.15 (Komi. Stretching also increases the length of ligaments. from the muscle tension-length characteristics. 1993).8. although the contraction speed increases and the time to reach peak tension decreases as the temperature is raised. These include increases in the maximal voluntary contraction (MVC). Also. Neural adaptations also occur to muscle with training (Enoka and Fuglevand. Stretching seems to have a significant effect on muscle at physiological lengths. Passive stretching of the muscle-tendon unit can alter its failure properties. 1. 1989). A series of short stretches results in greater adaptation than one held over a longer time. neurally regulated. the length-feedback component and the negative force-feedback component (after Komi. little consensus exists on how warm-up affects the mechanical properties of tissues. with short-term training and after mental MVC training. with stress relaxation being greatest during the early part of the stretch. where stress relaxation predominates.4 WARM-UP Surprisingly. 1993). contralateral limb strength increases (cross-education) of up to 25% (compared with 36% in the trained limb) have been found with no size or enzyme changes (Enoka and Fuglevand. Increasing .
and its significance for biological materials. what would be the most important properties for materials for use in: a vaulting pole. was explained. Outline the most important material and mechanical properties of cartilage. 6. 1. contractility. mechanical stiffness.10 Exercises . muscle activation.Exercises temperature also increases the isometric endurance time. describe the following properties and behaviour of skeletal muscle: elasticity.12). The mechanical properties of connective tissue can be altered. 4.9 Summary 1. and briefly explain. 3. age. skis. the ways in which various factors—immobilisation. cartilage. muscle stiffness and the importance of the stretch-shortening cycle were all described. reduces muscle stiffness and increases the peak power production. After consulting at least one of the first two items for further reading (section 1. 1993a). were considered. Define stress and strain and provide clear diagrams of the different types of loading. Provide a biomechanical subdivision of the factors that affect injury and list the factors in each category. Give your opinion about which of these are intrinsic and which extrinsic to the sports participant. List. Muscle elasticity contractility. The composition and biomechanical properties of bone. the frame of a squash racket. describe the differences between the behaviour of a material that is viscoelastic and one that is not. a racing bicycle frame. Using clearly labelled diagrams (such as stress-strain diagrams) where necessary. through combined temperature and load changes. explain the material properties related to elasticity and plasticity. sex. exercise and training—affect the properties of biological tissue were outlined. muscle activation. rowing oars. and the stretch-shortening cycle. ligament and tendon. 7. Finally. the last by 4%/°C (Best and Garrett. 31 In this chapter the biomechanical reasons why injuries occur in sport were covered. this might support the use of a warm-up routine followed by stretching (Best and Garrett. and their behaviour under various forms of loading. Draw up a table summarising the properties of bone in tension and compression and shearing and bending. You should find Easterling (1993) useful further reading. The most important mechanical properties of sports materials were considered. Using a clearly labelled stress-strain diagram for a typical non-biological material. 5. maximum force. Viscoelasticity. the generation of maximal force in a muscle. to increase joint range of motion. 2. 1. 1993a).
A. Blackwell Scientific.F. Bartlett. Grood.R. pp. sex. London.L. and Gould. Natural History Museum. age. (1984) Tendinitis: its Etiology and Treatment. (1993) Advanced Materials for Sports Equipment. Draw a clearly labelled stress-strain diagram for a collagenous material. Propose and justify two examples from sport and exercise in which one or more of each of the properties of non-biological and biological materials considered in this chapter are important. and Garrett. in Sports Injuries: Basic Principles of Prevention and Care (ed. and Edgerton. pp.32 Causes of injury/properties of materials 8.Renström). A. London. in Sports Injuries: Basic Principles of Prevention and Care (ed.12).A. CRC Press.F. London. 71–86. 125–182. pp. R. Collamore Press. E & FN Spon.M. 54–70. Chapman. (1997) Introduction to Sports Biomechanics. (1975) Effects of training and disuse on connective tissue. Oxford University Press. pp. describe fully the properties of collagenous materials. Best. in Natural and Living Biomaterials (eds G. K. Lexington. Franklin Institute Press. Best. (1985) The mechanical properties of human muscle. Oxford. R. (1993b) Muscle-tendon unit injuries.A.Terjung). England. in Exercise and Sport Sciences Reviews—Volume 13 (ed. Easterling. Booth. pp. London.W. K. London. in Exercise and Sport Sciences Reviews—Volume 3 (ed. and Garrett.Y. USA. 43–60. R. P. Edington.L.H. Biewener. A. and Stanish. P.E. Chapman & Hall. exercise and training.Terjung). W. A. 10. S. London. (1978) Biomechanics of ligaments and tendons. Boca Raton. P. USA. in Biomechanics—Structures and Systems: a Practical Approach (ed.D.W. E.H. pp. Curwin. D.R. England. F. Franklin Institute Press. D.Hastings and P. MacMillan.L. USA. MA. USA. New York. Blackwell Scientific. R. T.. England. Houghton Mifflin. New York.A.W.F. 84–112. E. Chan. warm-up.W. S. (1993a) Warming up and cooling down. pp. Boston. F. England. R.McN.A. such as ligament or tendon. W.Terjung).H. and Noyes. in Sports Injuries: Basic Principles of Prevention and Care (ed. New York. 1.12 ). (1992) The Human Machine. After consulting at least one of the items for further reading (section 1.E. England.L.E.11 References Alexander. USA. (1993) Cartilage and ligament injuries.Renström). England. FL. After consulting at least one of the items for further reading (section 1.M. . Butler. and Hsu. 1–20. USA.Biewener).S. Bonfield. describe how each of the following factors affect the properties of biological tissue: immobilisation and disuse.E. W. T. V. in Exercise and Sport Sciences Reviews—Volume 6 (ed. pp. NJ. (1992) Overview of structural mechanics.M. 9.Ducheyne). England. 242–251. (1984) Elasticity and viscoelasticity of cortical bone.C.Renström). (1976) The Biology of Physical Activity. Blackwell Scientific. W. 443–501.M.
Renström).D.).Landers et al. in Biomechanics of the Musculoskeletal System (eds B. Fleck. (1982) Biomechanics of long bone injuries.J.Holloszy). D. 151–168. Human Kinetics. Schellock. England. pp. G. Komi).Gozna and I. Komi.O. IL. pp. Renström). et al. 16–23.Skinner. Champaign. M. 1–34.Landers et al. Champaign. Grabiner). pp.S. Wiley. in Future Directions in Exercise and Sport Science Research (eds J. C.A.J. Blackwell Scientific. Baltimore.J. pp.J.. Baltimore. B.V. J.References Enoka. A. in Sports Injuries: Basic Principles of Prevention and Care (ed. F. Champaign.S. pp. P.M. (1993b) Body composition and predisposing diseases in injury prevention.Corbin. P.H. Champaign. D.Herzog).J. 926–934. 362–397.Nigg and W.O. in Current Issues in Biomechanics (ed. pp. USA..H. IL.Komi). in Biomechanics of the Musculoskeletal System (eds B. Kannus. Williams & Wilkins. 2740–2744. in Exercise and Sport Sciences Reviews—Volume 24 (ed. W. T. Kraemer. (1992) Physiological cross-sectional area of human leg muscles based on magnetic resonance imaging.R. M.Herzog). Roy. in Sports Injuries: Basic Principles of Prevention and Care (ed. Human Kinetics.B.M. Gregor. 161–177. J. USA. and Evans.D. Journal of Applied Physiology. England. Williams & Wilkins. pp. pp. MD. USA. W. P. R. (1993) Ligamentous receptors: the neurosensory hypothesis. USA. pp.L. Gottlieb. Wiley. MD. 115–135. 33 . Human Kinetics. Human Kinetics. in Strength and Power in Sport (ed. 169–179. P. (1993) Muscle-fibre pennation angles are greater in hypertrophied than in normal muscles. 106–132.M.D.D. Blackwell Scientific.R.Grabiner). Abe. in Exercise and Sport Sciences Reviews— Volume 24 (ed. pp. (1993) Ligament biomechanics. IL.Harrington). USA. pp. Komi. C. (1993) Skeletal muscle mechanics and movement. pp. USA.Corbin. (1996) Strength and power training: physiological mechanisms of adaptation. D. in Future Directions in Exercise and Sport Science Research (eds J. Human Kinetics. W. and Fuglevand.. pp. in Current Issues in Biomechanics (ed M.M. (1993a) Types of injury prevention.F. 10.Grabiner).B.B. (1995) Ligaments. E. Skinner. IL. Y. 133–153. USA. T. R. England. in Strength and Power in Sport (ed. USA. Blackwell Scientific.J. Champaign. N. Baltimore. in Current Issues in Biomechanics (ed M.V. Champaign.G. and Shrive.V. (1989) Future directions in biomechanics research: neuromuscular performance. P. (1993) Neuromuscular basis of the maximum voluntary force capacity of muscle. IL. R. P. Kawakami. P. Gozna. P. Oxford. Kannus. IL. 171– 211. Fukunaga.A.D. Hawkings. 1–29. (1989) Locomotion: a commentary. P.Holloszy). Huijing. T. Blackwell Scientific. C.A. Chichester. Williams & Wilkins. M. R. (1992) Stretch-shortening cycle. in Biomechanics of Musculoskeletal Injury (eds E. 215–235. S. and Fukunaga. Journal of Orthopaedic Research.J.). USA. Gregor. and Loitz. pp. Oxford. Chichester.Nigg and W. Human Kinetics. 123–150.F. Frank. 237–254. pp. England.M. (1995) Tendon. Herzog. Grabiner. (1992) Elastic potential of muscle. in Current Issues in Biomechanics (ed. England. 76.V. London. Grabiner). England. MD. (1996) Muscle compliance: implications for the control of movement. London. 45–56.
-P. pp. de Meester. Springfield. B. (1973) Kinesiology of the Human Body. and Komi. W. C.W. MD.E. (1993) Excessive loads and sports-injury mechanisms. P.1). pp. (1993) Incidence and severity of sports injuries. Nordin.Renström). Nigg. and Frank. and Nordin. Martens. M. S. and Herzog. USA.H. Zajac. Wiley.F. M. pp. Nigg. 79–105. (1995) Analytical representation of muscle line of action and geometry.-Y. in Biomechanics of the Musculoskeletal System (eds B.J. (1993) Muscle coordination of movement: a perspective. in Exercise and Sport Sciences Reviews—Volume 23 (ed. pp.G. England. B.Woo and B.Ducheyne). van Audekercke. Moffroid. pp. pp.Herzog). pp. Blackwell Scientific. J. (1980) The mechanical characteristics of the long bones of the lower extremity in torsional loading. in Sports Injuries: Basic Principles of Prevention and Care (ed.Renström). England.Renström). 24–38. 107–119.L. 89–98. R. England. England. Chichester.F.M. C. I. P. V. F. in Biomechanics of the Musculoskeletal System (eds B.A.Schmid-Schönbein. Lea & Febiger. PA. Boca Raton.M. van Audekercke. Steindler. (1986) Biomechanics of tendons and ligaments. M. New York.A. USA.-Y.W. (1995) Articular cartilage. (1991) Fundamentals of Biomechanics. 44. M.O. 120–134. CRC Press. Journal of Biomechanics. (1994) Bone. P. W. in Sports Injuries: Basic Principles of Prevention and Care (ed. Özkaya. (1984) An alternative view of the concept of utilisation of elastic in human movement. Springer Verlag. USA. Blackwell Scientific. P.C.. London. in Frontiers on Biomechanics (eds G. USA.H. (1993) Biomechanical response of body tissue to impact and overuse. (1993) Strategies for the prevention of musculoskeletal injury. in Three-Dimensional Analysis of Human Movement (eds P.G. P. London.34 Causes of injury/properties of materials Loitz. and Martens. J. van Ingen Schenau. England.M.. A. R. Wiley. IL. S. and Frank. (eds) (1989) Basic Biomechanics of the Musculoskeletal System. pp. P.F. B. USA. Human Movement Science. power-and elasticity-velocity relationships in walking.Nigg and W. MA.A. N. and Mulier. Pope. European Journal of Applied Physiology. M. (1980) Force-.D. Journal of Biomechanics. Shrive.T. running and jumping.Nigg and W.L.Herzog). 279–289.A. London.A. USA. J.B.H. New York. Thomas. . Chichester.F. England. 3–15.H. Nigg. 215– 256. Philadelphia. 26(Suppl. van Mechelen. Champaign. M. 33–64. B. and Frankel. Pierrynowski.V.H.W. S. 180–195.M.Holloszy). 301–336.Hastings and P. (1994) Biomechanics of the Musculoskeletal System. (1984) Mechanical properties of cancellous bone. in Sports Injuries: Basic Principles of Prevention and Care (ed.Blanchi). Wiley.H. (1993) Biology and mechanics of ligament and ligament healing. England.K. 109–124. in Natural and Living Biomaterials (eds G.F. Chichester. Van Nostrand Reinhold. and Grimston. pp. Blackwell Scientific. Baltimore.Stokes and J. Woo.M. M. Williams & Wilkins. 3. Luhtanen. N.R. B. in Sports Injuries: Basic Principles of Prevention and Care (ed.Zweifach). USA. pp. FL. Human Kinetics. 48–78. P.B. 667–676. and Beynnon. 13.Renström). London.Allard. Blackwell Scientific.
Chapters 13–17. A good and less mathematical summary of similar material to that in Nigg and Herzog (1994). Philadelphia. pp. PA.M. M. R. Lea & Febiger. B. C. (1991) Fundamentals of Biomechanics. D.F. England. W. (1989) Movement dynamics and connective tissue adaptations to exercise. USA. IL. and Nordin.S. USA. Van Nostrand Reinhold. Blackwell Scientific. London. pp. but the text is very clearly written. articular cartilage. Skinner. England. Nigg. Chichester. insight into non-biological materials for sport is provided by: Easterling. Champaign.12 Further reading . (1993) Advanced Materials for Sports Equipment. in Sports Injuries: Basic Principles of Prevention and Care (ed. This provides a good summary of the biomechanics of bone. C.Further reading Zernicke. Many sport and exercise scientists may find the mathematics a little daunting in places.B.A. 43–53.M. mostly non-mathematical.F.H. Chapters 1 to 3 and 5. London. (eds) (1994) Biomechanics of the Musculoskeletal System. A good. England. Chapter 2. Biomaterials.). and Frankel. Chapman & Hall. M.E. P. Human Kinetics. Wiley. ligament. (eds) (1989) Basic Biomechanics of the Musculoskeletal System. Zetterberg.H. 1. USA. and Herzog. This contains detailed explanations of the mechanics of deformable bodies. (1993) Bone injuries. 35 The following three references expand on the core material of this chapter. V. including biological tissues.Corbin. K. New York. Nordin.Landers et al. in Future Directions in Exercise and Sport Science Research (eds J. muscle and joints. Özkaya. N. tendon. but is mathematically somewhat advanced in places.Renström). 137–150.
Traumatic. cartilage and the muscletendon unit (Pecina and Bojanic. tendons. the failure strength . Overuse injuries result from repetitive trauma preventing tissue from self-repair and may affect bone. or acute. we noted that injury occurs when a body tissue is loaded beyond its failure tolerance. Injuries are often divided into traumatic and overuse injuries. injury has a rapid onset and is often caused by a single external force or blow. they occur because of microscopic trauma (or microtrauma). the back and the neck • appreciate the effects that genetic and fitness and training factors have on injury. or other structure. 1989). ligaments and the muscle-tendon unit • understand the sports injuries that affect the major joints of the lower and upper extremities. 1993). 2.1 Introduction In Chapter 1. bursae. more attention will be paid to these injuries than to those affecting bones. In this chapter. As discussed in Chapter 1. Appendix 2.2 Injuries in sport: how the body behaves under load This chapter is intended to provide an understanding of the causes and types of injury that occur in sport and exercise and some of the factors that influence their occurrence. including cartilage. After reading this chapter you should be able to: • understand the terminology used to describe injuries to the human musculoskeletal system • distinguish between overuse and traumatic injury • understand the various injuiries that occur to bone and how these depend on the load characteristic • describe and explain the injuries that occur to soft tissues. we will focus on sport and exercise injuries that affect the different tissues and parts of the body. at the end of this chapter. Overuse injuries are associated with cyclic loading of a joint. at loads below those that would cause traumatic injury (Andriacchi. Because most of the injuries that occur in sport and exercise affect the joints and their associated soft tissues.1. provides a glossary of possibly unfamiliar terms relating to musculoskeletal injury.
1a).2. 1993).1a). bending and torsion which lead to the following five basic patterns of fracture (Table 2. 2. 1993). A high frequency of load repetitions (as in step aerobics) is more damaging than a low frequency. and the number of load repetitions—and the material and structural bone characteristics (Gozna. examples of which include the Y type supracondylar fracture of the femur or humerus. 1993). for example.1b.1). shoes and surfaces have been implicated (Williams. muscle imbalance. The relationship between overuse injuries and the factors that predispose sports participants to them have been investigated for some sports. anatomy.1 TYPE OF FRACTURE Fractures are rarely caused by tension. However. The fractures are microscopic and should. The diaphyseal bone is driven into the thin metaphyseal bone producing the fracture pattern most common from axial loading (Table 2. Impact. Stress fractures are most likely during sustained. that under tension (to . but that have been repeated many times. Figure 2. 1982). no empirical studies have been reported that identify the specific mechanism for overuse injuries in distance runners. more correctly. Bone injuries are mostly fractures. muscle-loading or excessive movement may all be contributory factors (Williams. For distance runners. strenuous activity when fatigued muscles might fail to neutralise the stress on the bone (Zetterberg. 1993). these are traumatic when associated with large loads. Because cortical bone is weaker in tension than compression. training errors. 37 Bone injuries depend on the load characteristics—the type of load and its magnitude.2 Bone injuries 2. Diaphyseal impaction fractures These are usually caused by an axial compressive load offset from the longitudinal axis of the bone. until the endurance limit is reached (Figure 1. Traumatic fractures are the most common injuries in horse-riding.6).Bone injuries decreases as the number of cyclic loadings increases. hang-gliding. The relationship between the type of load and traumatic fractures is discussed in the next section. Transverse fracture These are usually caused by a bending load (Table 2. but by various combinations of compression. roller skating and skiing (van Mechelen. ‘Stress’ fractures are overuse injuries sustained at loads that are within the normal tolerance range for single loading. the load rate. be termed fatigue fractures as all fractures are caused by stresses in the bone.
causing the bone under tension to open up. No agreement exists about whether the . The failure mechanism is crack propagation at right angles to the bone’s long axis from the surface layer inwards. in Figure 2. Spiral fractures Spiral fractures (Table 2. The spiral propagates at an angle of about 40–45° to the bone’s longitudinal axis.1a) fails before that being compressed. NA.1 Basic fracture patterns (after Gozna.1c) are relatively common in sport. usually in combination with other loads. The diaphysis of any long bone subjected to a bending load can be affected. They are caused by torsional loading. 1982) the right of the neutral axis.38 Injuries in sport: the body under load Table 2.
.1 Fractures: (a) transverse. 1982).Bone injuries 39 Figure 2. (b) butterfly and oblique transverse (after Gozna.
1b. and in the soft tissues around the bone. These fractures can occur when the thigh or calf receives a lateral impact when bearing weight. and in overarm throwing movements. Greater energy causes more tissue to be destroyed and a more complex fracture. The greater the magnitude of the load.1e.3 LOAD RATE As discussed in Chapter 1. 2. as in oblique. If the axial and bending stresses are of similar magnitude. butterfly and comminuted fractures. caused by the bending load impacting the oblique ‘beak’ against the other bone fragment (Gozna. breaking the intermolecular bonds (fracturing). It requires . on one side of the bone’s neutral axis the bending stress is compressive (C in Figure 2. On the other side of the bone’s neutral axis the bending stress is tensile (T in Figure 2. the resultant oblique transverse fracture is a combination of the two.2.1b). from the tip of the ski catching in the snow and producing large lateral torques in the calf. bone. the greater the amount of energy associated with its application. This stress combination is equivalent to a bending load at an oblique angle. Oblique transverse and butterfly fractures These (Table 2.40 Injuries in sport: the body under load fracture mechanism is caused by shearing within the bone or by the tensile failure of intermolecular bonds (Gozna. This energy is dissipated in deforming the bone. oblique transverse.1c.1b) are caused by a combination of axial compression and bending. where the implement’s inertia creates a large torque in the humerus. 2. failure in tension due to bending. along with other biological materials. this can partially cancel the axial compressive stress. failure in compression. The butterfly fracture is a special case. is viscoelastic.1b) and is cumulative with the axial compressive stress. Typical examples occur in skiing. its mechanical properties vary with the rate of loading. and part transverse. as in tackles. hence the fracture pattern in Table 2. it is part oblique. 1982). Figure 2. As in Figure 2.2 MAGNITUDE OF LOAD If the magnitude of the load exceeds the strength of a particular structure. Oblique fractures These occur under combined compressive and bending loads with a less important torsional contribution. The combined effect is shown in Figure 2.1a. 1982). that structure will fail.2.
Bone injuries more energy to break bone in a short time (such as an impact) than in a relatively long time, for example in a prolonged force application. However, in such a short time, the energy is not uniformly dissipated. The bone can literally explode, because of the formation of numerous secondary fracture lines, with an appearance resembling a comminuted fracture.
2.2.4 BONE PROPERTIES The material properties of bone were considered in the previous chapter. As noted there, the most important structural property is the moment of inertia, which influences how the shape of the bone resists loading. Both the moment of inertia about the transverse axis (bending resistance) and the polar moment of inertia about the longitudinal axis (torsional resistance) are important. The moment of inertia determines where a bone will fracture; for example, torsional loading of a limb leads to the occurrence of a spiral fracture at the section of minimum polar moment of inertia, even though the cortex is thickest there. Stress concentration, as noted in Chapter 1, is an important consideration in material failure. For bone, stress concentration often occurs at a previous fracture site, from a fixation device or callus (Gozna, 1982). It has recently been proposed that stress fractures tend to occur in regions of bone in which high localised stress concentrations have been caused by repetitive impact loads. This is associated with muscular fatigue leading to the diminution of stress-moderating synergistic muscle activity. It has also been hypothesised that this effect may be influenced by the remodelling process of bone, which begins with resorption—temporarily reducing bone mass (Burr, 1997).
Joint injuries can involve bone or one or more of the associated soft tissues, such as the cartilage, ligaments and muscle-tendon units considered in the following sections. The synovial membrane, which provides fluid to lubricate synovial joints, can also be injured, producing haemarthrosis leading to adhesions, restriction of movement and joint stiffness. Soft tissue injuries involve the cell-matrix responses of inflammation, repair and degeneration (Leadbetter, 1993). Acute and overuse soft tissue injuries have different clinical injury profiles. Both have a period of raised vulnerability to reinjury (Figure 2.2a,b). In overuse injury, repetitive injury through overexertion can lead to accumulation of scar adhesions and a cycle of reinjury (Leadbetter, 1993).
2.3 Joint and soft tissue injuries
Injuries in sport: the body under load
Figure 2.2 Hypothetical injury profiles: (a) acute macrotraumatic tissue injury, e.g. partial tendon strain or lateral-collateral ligament sprain; (b) chronic micro-traumatic soft tissue injury, e.g. overuse injury of tendons (after Leadbetter, 1993).
2.3.1 ARTICULAR CARTILAGE Functionally responsible for control of motion, transmission of load and maintenance of stability, articular cartilage is plastic and capable of deformation, decreasing the stress concentration by increasing the loadbearing area. Cartilage injuries occurring without a fracture may be related to overuse arising from excessive training programmes (Chan and Hsu, 1993). Repetitive loading that exceeds the ability of the cartilage to respond causes the cartilage to wear away leading to osteoarthritis (Pope and Beynnon, 1993). Impact loads exceeding normal physiological limits can lead to swelling of the cartilage, and repeated impacts are a possible mechanism in cartilage damage (Nigg, 1993). If trauma is extensive or severe enough, the cartilage matrix may fracture or fissure (Chan and Hsu, 1993).
2.3.2 LIGAMENTS Ligaments stabilise joints and transmit loads; they also contain important mechanoreceptors (Grabiner, 1993). They are subject to sprains, caused by excessive joint motion, most of which are not severe (see Appendix 2.1). Direct blows to a joint can cause stretching of ligaments beyond the normal physiological range and permanent deformation. Ligament failure is often caused by bending and twisting loads applied distally to a limb as, for example,
Joint and soft tissue injuries in a tackle. Failure depends on the load rate and is normally one of three types (Chan and Hsu, 1993; Hawkings, 1993). First, bundles of ligament fibres can fail through shear and tension at fast load rates; this midsubstance tear is the most common mechanism of ligament injury. Secondly, bony avulsion failure can occur through cancellous bone beneath the insertion site at low loading rates; this occurs mostly in young athletes, whose ligaments are stronger than their bones. Finally, cleavage of the ligament-bone interface is possible, although rare because of the strength of the interface. Ligaments may experience microstructural damage during strenuous activities leading to overuse injury. The most obvious effect of ligament tears is a loss of stability, other effects being joint misalignment, abnormal contact pressure and loss of proprioception (Chan and Hsu, 1993). The recovery timescale is one to seven days’ inflammation, then up to three weeks for proliferation of connective tissue. From the third to sixth weeks, the nuclei of the fibro-blasts align with the long axis of the ligament and remodelling starts, although this may take several months to complete (Hawkings, 1993). Mechanically, the healed ligament does not recover its cyclic behaviour or stress relaxation characteristics; its strength after recovery is, at most, 70% of its original strength (Chan and Hsu, 1993). Protective equipment, such as taping, knee and ankle braces and wrist guards can help to prevent ligament sprains. However, such equipment might increase the severity of injury, for example in lateral impacts to the braced knee. Sports participants with excessive ligament laxity, previous ligament injury or poor muscle strength are particularly vulnerable to ligament injury.
2.3.3 MUSCLE-TENDON UNIT The muscle-tendon unit causes movement and stabilises and absorbs energy in load transmission. The muscle-tendon junction is a crucial element linking the force-generating muscle fibres and the force-transmitting collagen fibres of the tendon. Muscle injuries can be traumatic, e.g. a contusion, or overuse, and can involve damage to the muscle fibres or connective tissues. Delayedonset muscle soreness (DOMS) can follow unaccustomed exercise, normally peaking two days after activity and affecting the tendon or fascial connections in the muscle (Best and Garrett, 1993a). Direct trauma to muscle fibres (particularly quadriceps femoris and gastrocnemius) frequently leads to an intramuscular haematoma and can result in calcification at the injury site (myositis ossificans). Compartment syndromes are associated with increased pressure within an anatomically-confined muscle compartment. Acute compartment syndromes usually result from overuse, muscle rupture or direct impact (Kent, 1994). Chronic compartment syndromes are caused by an increase in muscle bulk after prolonged training. They are far more common than
Injuries in sport: the body under load acute compartment syndromes, and are usually associated with pain and aching over the anterior or lateral compartments after a long exercise bout. Medial tibial syndrome (shin splints), occurring on the distal third medial aspect of the tibia, is the most common overuse injury to the lower leg (e.g. Orava, 1994). Although often classed as a compartment syndrome, it is most likely a repetitive-use stress reaction of the bone or muscle origin (Best and Garrett, 1993a). The muscle-tendon unit is subject to ruptures, or tears, and strains induced by stretch. Such strains are often cited as the most frequent sports injuries, and are usually caused by stretch of the muscle-tendon unit, with or without the muscle contracting. They occur most commonly in eccentric contractions, when the active muscle force is greater than in other contractions and more force is produced by the passive connective tissue (Best and Garrett, 1993a). Multi-joint muscles are particularly vulnerable as they are stretched at more than one joint. These muscles also often contract eccentrically in sport, as when the hamstrings act to decelerate knee extension in running. Sports involving rapid limb accelerations, and muscles with a high type II fibre content, are frequently associated with strain injuries. Injuries may be to the muscle belly, the tendon, the muscletendon junction or the tendon-bone junction, with the last two sites being the most frequently injured. The increased stiffness of the sarcomeres near the muscle-tendon junction has been proposed as one explanation for strain injury at that site (Best and Garrett, 1993a). The muscle-tendon junction can be extensive; that of the semimembranosus, for example, extends over half the muscle length. Fatigued muscle is more susceptible to strain injuries, as its capacity for load and energy absorption before failure is reduced. Stretch-induced injuries are accompanied by haemorrhage in the muscle. An inflammatory reaction occurs after one to two days and this is replaced by fibrous tissue by the seventh day. By this time, 90% of the normal contractile force generation will have been recovered. However, the passive, non-contracting strength recovery is less (77%) by that time and scar tissue persists, predisposing a muscle to a recurrence of injury (Best and Garrett, 1993a). Injuries to a tendon are of three types: a midsubstance failure, avulsion at the insertion to the bone, and laceration. The first two types can occur in sport owing to vigorous muscle contraction (Pope and Beynnon, 1993). Acute tendon injury often involves a midsubstance rupture at high strain rates (Leadbetter, 1993).
Sports injuries to joints and tissues The following subsections provide some examples of injuries to the joints and tissues of the body that occur in sport. These are only a few of many examples; they have been chosen to provide an insight into the biomechanics of sports injury. For an epidemiological approach to sports injuries, refer to Caine et al. (1996).
2.4 Sports injuries to joints and associated tissues
2.4.1 THE PELVIS AND THE HIP JOINT Because of its structure, the pelvis, despite being composed largely of cancellous bone with a thin cortex, has tremendous strength. Additionally, cancellous bone has shock-absorbing properties that help to reduce stress concentration. The freedom of movement at the hip and spinal joints minimises the transmission of bending and torsional forces to the pelvis. For these reasons, pelvic girdle injuries are uncommon in sport; when they do occur (for example in rugby) compression loads of high energy are normally responsible. In walking, the hip joint has forces of three to five times body weight (BW) to transmit. The hip joint forces that result from ground impact, such as those experienced in running, are obviously much greater. The most common fracture is to the femur when subject to a combination of axial compression, torsion, shear and bending loads. The force transmitted from the hip joint to the femur has shear, compressive and bending components (Figure 2.3) which can cause fracture at various sites. Stress fractures to the femur neck and shaft have increased and are associated with repetitive loading in long- and middle-distance runners and joggers (Renström, 1994a). Injuries to the muscle-tendon units are the most common, particularly to the rectus femoris, adductor longus and iliopsoas, with the first of these the most susceptible (Renström, 1994a). Muscle tears and strains, particularly to the two-joint muscles, can be caused by sudden strain on an incompletely relaxed muscle, either by a direct blow or indirectly as in sprinting. Hamstring tendinitis commonly affects biceps femoris at its insertion. Other injuries include osteitis pubis, a painful inflammation of the symphysis pubis, which is common in footballers and also affects runners and walkers.
2.4.2 THE KNEE The knee, consisting of the patellofemoral and tibiofemoral joints, is vulnerable to sports injury, particularly the tibiofemoral joint. The peak resultant force at this joint (3–4 BW in walking) is located in the medial
(b) shear component (S) causing downward displacement of femoral head relative to shaft.46 Injuries in sport: the body under load Figure 2. (d) varus moment (M) of hip joint force (F) tilts the femoral head. here r is the moment arm of force F (after Harrington.3 Hip joint forces: (a) force vector (F). . 1982). (c) compression component (C) causing impaction of femoral head and neck.
The anterior cruciate ligament is the knee ligament that suffers the most frequent total disruption (Pope and Beynnon. Meniscus tears involve shear and compression. Under such trauma. 1994). 47 . as in a rugby tackle. One of the most common knee ligament injuries arises from combined axial loading with abduction and external rotation. The first of these is exacerbated by sports. the anterior cruciate ligament if the knee is almost completely extended (Moore and Frank. and tibial stress injury (Maclntyre and Lloyd-Smith. or as well as. The most common overuse running injuries are patellofemoral pain syndrome. The bending moment tending to adduct the calf relative to the thigh (varus angulation) is balanced by the joint force and the tension in the lateral collateral ligament. During part of the normal gait cycle.4a). During the normal gait cycle the knee is loaded in various ways: abduction-adduction (bending). particularly when combined with shear stress and axial compression across the load-bearing surfaces. Soft tissue injuries. and the medial collateral ligament provides stabilisation (Figure 2. 1993). comminution and depression of the articular surfaces can occur with shearing of the femoral or tibial condyles. Contusions to the knee are usually caused by a direct blow and are common in sport. torsion. The menisci act as shock absorbers and provide anteroposterior and medial-lateral stabilisation owing to their shape. The posterior cruciate ligament may be torn instead of.Sports injuries to joints and tissues compartment. This loading can result in tearing of the medial collateral and anterior cruciate ligaments and the medial meniscus. Dehaven and Lintner (1986) reported ligament injuries to account for 25–40% of sports injuries to the knee.4b). In noncontact injuries. are more common than fractures. 1993). The lateral ligaments resist both abduction or adduction and torsional loads. particularly to the ligaments. friction syndrome of the iliotibial band. the cruciate ligaments prevent anteroposterior displacement of the tibia relative to the femur and resist knee hyperextension. and shear (parallel to the joint surfaces). 1994). Adams (1992) reported that 9% of injuries in the sports medicine clinic at his hospital involved knee ligaments. 1993). fascia lata and biceps femoris (Figure 2. the point at which the resultant joint force can be considered to act moves to the lateral compartment. such as volleyball and basketball. This is typically caused by a valgus load applied when the foot is on the ground bearing weight and the knee is near full extension. Traumatic abduction–adduction moments can rupture collateral ligaments or lead to fracture. Bursitis affects many of the bursae of the knee. where the forces at the patellofemoral joint are large (Marzo and Wickiewicz. Pure axial compression can cause a Y or T condyle fracture when the femoral shaft impacts with the condyles causing them to split off (Table 2.1a). They are usually caused by the body rotating around a fixed knee that is bearing weight. particularly soccer. large accelerations with a sudden change of direction are often responsible (Pope and Beynnon. axial compression.
1982).4 Knee joint lever systems when calf is: (a) adducted. . (b) abducted (after Harrington.48 Injuries in sport: the body under load Figure 2.
important in many sports. A small moment in the frontal plane (up to 0. The foot is often divided into the rearfoot. Patellar tendinitis. the latter formed by the metatarsal bones and associated plantar ligaments. and the intrinsic muscles. The extrinsic muscles are responsible for the gross movements of the foot. It is usually experienced by runners with large training mileages. and those to the tibiofibular ligament by forced dorsiflexion.4.5a). 1994). It is often caused by minor gait or foot abnormalities or by friction with the heel tab (the sometimes misnamed ‘Achilles tendon protector’) on some running shoes. Tendinitis is common in runners and involves the tibialis posterior tendon (behind the medial malleolus) or the peroneal tendons (behind the lateral malleolus). sprinting or swerving movements occur (Puddu et al. Achilles tendon injuries occur in many of the sports that involve running and jumping.16 BW in walkers) transmits load to the lateral malleolus. The foot is. The arches are important to the shock absorbing properties of the foot. which originate in the leg. and 85% of these involve the lateral ligaments (Grana. Its bones are arranged in two arches. 1994). involved in two-thirds of all ligamentous ankle injuries (Karlsson and Faxén. the lateral malleolus is most commonly affected (Grana. which have origins and insertions within the foot. as is the fat pad under the heel. 49 2. 1994). with the deltoid ligaments. Bursitis affects the superficial bursa over the Achilles tendon insertion and can be caused by blows or by friction from the heel tab. 1994). accounting for around 10–15% of total injuries. 1992). During running. of course. is often associated with sports such as basketball that involve eccentric contractions and jumps and landings from. 1994). The most vulnerable of the ligaments is the anterior talofibular. their tendons are susceptible to overuse injuries.. Soft tissue injuries include various ligament sprains and inflammations of tendons and associated tissues. the forces applied to the foot exceed three times body weight. the longitudinal (Figure 2. prevents talar eversion. those to the medial ligament by eversion. Peritendinitis involves swelling and tenderness along the medial border of the Achilles tendon.3 THE ANKLE AND FOOT The ankle is the most commonly injured joint in sport. midfoot and forefoot regions (Figure 2. a hard surface (Adams. and on to. Foot injuries are affected by variations in foot anatomy (section . About 15% of traumatic sports injuries involve sprain of the ankle ligaments. The stress concentration is high owing to the small load-bearing area.Sports injuries to joints and tissues with the prepatellar bursa being most susceptible because of its location (Marzo and Wickiewicz.5b) and transverse. Fractures to the ankle in sport are relatively infrequent. or ‘jumper’s knee’. Complete rupture of the Achilles tendon is most frequent in sports where abrupt or repeated jumping. The medial malleolus. The foot is moved by the extrinsic muscles. Sprains to the lateral ligaments are caused by plantar flexion and inversion loads.
Traumatic fractures occur most frequently in collision sports or because of a fall (Martin. (b) longitudinal arch.50 Injuries in sport: the body under load Figure 2. is transmitted along the whole upper extremity as an axial compression force and a bending moment (Harrington.2) and the shoe–surface interface (chapter 3). with stress fractures usually involving the calcaneus. A load applied to the outstretched hand.5. 1982). half of these are overuse injuries.4.5 The foot: (a) regions of the foot.4 THE WRIST AND HAND The proportion of sports injuries that affect the wrist and hand depends on the involvement of the upper extremity. Injuries to the wrist and hand include dislocation and subluxation. 2. navicular and metatarsal bones. 1994). as in a fall. 2. Plantar fasciitis and stress fractures are common overuse injuries in runners and walkers. it is around 20% (Mitchell and Adams. Over 15% of sports injuries involve the foot. 1994). Waist fracture of the scaphoid is caused by falls on an .
1982). ‘Golfer’s elbow’ (medial epicondylitis) affects the flexor tendon origin on the medial epicondyle. Overvigorous action of the triceps in throwing can cause similar injuries.5 THE ELBOW Fractures can arise from the loading of the elbow in a fall on the outstretched hand (Harrington.4. A blow to the hand causes an axial force plus a bending moment equal to the product of the force’s moment arm from the elbow and the magnitude of the force. particularly in sports involving repetitive movements. 1992). A fall on an outstretched hand can also cause fracture displacement of the lower radial epiphysis in young sportspeople (Rimmer. It often follows minor strain when a fully prone forearm is vigorously supinated. Tendinitis can occur in the wrist tendons. rock climbing. ‘Thrower’s elbow’ is a whiplash injury caused by hyperextension. 51 2.Sports injuries to joints and tissues outstretched hand or by a hand-off in rugby (Rimmer. affecting at some time around 45% of tennis players who play daily (Chan and Hsu. A direct blow on a flexed elbow axially loads the humeral shaft. for example. ‘Tennis elbow’ (lateral epicondylitis). 1992). badminton and canoeing. This loading causes tension in the medial collateral ligament and lateral compression of the articular surfaces and can lead to fracture of the radial neck or head and. Sprain or rupture of the collateral metacarpophalangeal and interphalangeal ligaments can also occur. Avulsion fracture of the lateral humeral epicondyle can be caused by sudden contraction of the wrist extensors that originate there.6a). joint dislocation or subluxation (Figure 2. The most common cause of elbow injuries is abduction (Figure 2. 1994). ‘Javelin thrower’s elbow’ is a . whose ligaments are stronger than bone. These include basketball. skiing. is the most common overuse injury of the elbow. It affects the extensor muscle origin on the lateral aspect of the elbow joint. It is an overuse injury of the wrist extensors and forearm supinators. In children. the extension moment leading to supracondylar fracture is caused by the ulna impacting into the olecranon fossa (Figure 2. squash.6c) with hyperextension loading. particularly in body contact sports. 1994). cycling. Strain or rupture of the finger extensor tendons may be caused by ball contact. such as tennis. particularly extensor carpi radialis brevis. A range of other wrist and hand injuries affects participants in many sports where wrist and hand involvement is pronounced. which also occurs in sports other than tennis.6d). Medial epicondyle fractures can be caused by valgus strain with contraction of the wrist flexors. and finger or thumb dislocations by body contact sports. golf and gymnastics (see Mitchell and Adams. leading to fracture or epiphysitis of the olecranon process. A blow to the outstretched hand can cause either posterior or anterior elbow dislocation.6b) or cause Y-or T-shaped fractures to the humerus articular surface. after medial ligament rupture. which may fracture the olecranon (Figure 2.
R. radius. C. strain of the medial ligament caused by failure to achieve the classic ‘elbowlead’ position. as in roundarm throwing (Thompson. 1992). (b) axial compression. compression.6 Mechanics of elbow injuries: (a) hyperextension moment. (c) abduction (valgus) moment. U. T. ulna. humerus. Abbreviations: H. tension (after Harrington.52 Injuries in sport: the body under load Figure 2. (d) dislocations and fractures from combination of abduction and hyperextension loading. 1982). .
the joints of the shoulder region often experience large ranges of motion at high angular velocities.g. It is common in sport. it is the second most common shoulder injury in American football (Mallon and Hawkins. 1992). such as javelin throwing and baseball pitching. 1994). In overarm sports movements. which is far less common. duration and magnitude of the impact and the magnitude of the acceleration of the head (van Mechelen. and impingement syndrome. infraspinatus and subscapularis. or occur through ‘whiplash’. and rupture or inflammation of the long head tendon of biceps brachii. Overuse injuries are common and frequently involve the tendons of the rotator cuff muscles that pass between the head of the humerus and the acromion process. can occur from a heavy frontal shoulder charge in field games or by a fall in which the head of the humerus is forced backwards while the humerus is inwardly rotated. 1993). Posterior dislocation. and fracture of the scapula in a direct impact. 53 2. Another injury that may be caused by such a fall. when the arm is fully abducted and externally rotated.4. 1994). is dislocation of the sternoclavicular joint. In the partially abducted arm. Anterior glenohumeral dislocation is most likely. Pecina and Bojanic. These injuries appear to be dependent on the configuration of the acromion process and to occur more in individuals with a hooked-shaped configuration along the anterior portion of the acromion (e.7 THE HEAD.6 THE SHOULDER A force transmitted along an adducted arm forces the head of the humerus against the coracoacromial arch resulting in injury to the rotator cuff muscles or the acromion.4. Fractures to the shoulder in sport include: avulsion fracture of the coracoid process in throwing. or in contact sports. 1994). The latter term is used to describe the entrapment and inflammation of the rotator cuff muscles. Marone. the ligaments of the acromioclavicular joint may also be affected. fracture of the acromion or glenoid neck in a fall on the shoulder.g. Other soft tissue injuries include supraspinatus calcification. particularly in young athletes. Impact injuries depend on the site. Chronic head injuries have been associated with repeated sub-threshold . Traumatic head injuries may be caused by a fall or collision. fracture of the clavicle is likely and this can also be caused by falls on the shoulder. the long head of biceps brachii and the subacromial bursa (e. Examples are tendinitis of the supraspinatus. For example. rupture of the supraspinatus tendon. for example in rugby. 1994).Sports injuries to joints and tissues 2. often with many repetitions (Mallon and Hawkins. triceps brachii tendinitis. The effect of protective headgear on such injury is considered in Chapter 3. BACK AND NECK Several studies have reported that head and neck injuries account for around 11% of the sports injuries that require hospital treatment (van Mechelen.
rotation causes a torsional load and axial loading leads to compression. 1994). the neural arches. 1982). intervertebral discs and the posterior longitudinal ligament resist compression. The vertebral bodies. The bending load caused by flexion compresses the vertebral body and increases the tension in the posterior ligaments. with an associated interdisc pressure of 70 kPa. In compression. extension and lateral flexion cause a bending load on the spine. A shear load is caused by any tendency of one part of the spine to move linearly with respect to the other parts (Evans.7). displacing nuclear material into the body of the vertebra as the disc disintegrates (Evans.7 The spinal ligaments under loading of a motion segment (after Evans. 1982).54 Injuries in sport: the body under load blows that can lead to a loss of psycho-intellectual and motor performance. bulging of the vertebral endplate can occur. 1982).g. Flexion. which can then crack at loads above 2. such as by head-first impact with an opposing player. Injury to the cervical spine has been associated with axial loading. .5 kN. when slight flexion has removed the natural cervical lordosis (Torg. such injuries have also been reported from repeated heading of fast-travelling soccer balls (e. The high elastic content of the ligamentum flavum pre-stresses the discs to about 15 N. van Mechelen. Most closely connected with boxing. particularly the interspinous Figure 2. 1994). capsule and interspinous ligaments resist tension (Figure 2.
Rotation of the extended spine can lead to rupture of the anterior longitudinal ligament. The probability of injury from a load of brief duration depends on both the peak acceleration and the maximum rate of change of acceleration (jerk) that occur (Troup. In the thoracic spine. The spine. javelin throwing. at some time. 1992). muscular strength. such as racket sports. Lateral bending or rotation combined with compression is usually responsible. Any of three injury-related activities may be involved. This may be exacerbated by any imbalance in the strength of the abdominal and back musculature. and particularly in sport and exercise. Although a single type of loading can cause injury. 1993). as the load on the anterior part of the vertebral body is three to four times greater than the tension in the ligament. Injury is more likely either when prolonged static loading occurs or in the presence of vibratory stress. skill and spinal abnormalities. rowing. weight-lifting and vertically jarring sports. Tensile loads on the spine can occur through decelerative loading in the abdominal region. particularly its cervical and thoracolumbar regions. and aerial movements in gymnastics and diving. and breaststroke and butterfly swimming. discus throwing. Overall the cervical spine is most prone to such injury. have been associated with twisting and other asymmetric movements because of high antagonistic muscle activity. 1989) and has several causes: the weakness of the region and the loads to which it is subjected in everyday tasks. High disc pressures. 1989): • Weight-loading. participants in sports such as tennis. Low-back pain affects. involving spinal compression. for example. This can result in failure of the posterior ligaments or in bone damage. Back-arching activities as in volleyball. such as running and horse-riding. the joint capsule and the posterior longitudinal ligament. These are (Rasch.Sports injuries to joints and tissues ligament which has a breaking force of around 2 kN. Rotation-causing activities involving forceful twisting of the trunk. Rotation of the flexed spine can lead to tearing of the posterior ligament. such as lifting. most of the world’s population (Rasch. Such loads result in fracture of the vertebral body before any ligament failure. golf. the spine is more likely to be damaged by combined loading. Limited extension at C5–6 and linked flexion at C6–7 and C7–T1 causes those regions to be particularly vulnerable to extension and flexion injury respectively. is highly vulnerable to torsion with discs. volleyball and skiing may be particularly vulnerable (Pope and Beynnon. which are between two regions of high torsional stiffness. joints and ligament all being susceptible to injury. for example in gymnastic bar exercises. 55 • • . Resistance to injury depends on the size and physical characteristics of the spine. which might lead to herniation. sudden torsion can injure the 10th to 12th thoracic vertebrae.
to a more side-on position at frontfoot strike. such as reduced strength. coordination). leg length. greater stresses in the smaller bones and articular surfaces. Inflexibility and muscle weakness caused by scar tissue may lead to compensatory changes in a movement pattern increasing the stress on a body segment elsewhere in the kinetic chain. such as generalised laxity.g. strength. coordination . 1993). these will be considered in the next subsection. Secondary dysfunctions are usually due to a previous injury. and proposed that their slower pace might be a compensatory factor.5. However. flexibility. 2. knee or back. The result is the common occurrence of spondylolysis (a stress fracture of the neural arch. or twisting.and knee-loading resulting from the wider female pelvis and greater genu valgum. with the following. at backfoot strike in the delivery stride. MacIntyre and Lloyd-Smith (1993) considered that overall. Although it is often symptomless. This counter-rotation. Here the bowler counter-rotates the shoulders with respect to the hips from a more front-on position. 2. it is far more common in. For further detailed consideration of all aspects of injury to the spine. Furthermore. flexibility and muscle coordination through proper training (MacIntyre and Lloyd-Smith. activities involving all three of these are more hazardous. such as age.g. they will be considered. 1995). fitness. AGE AND GROWTH Because of anatomical differences. anatomical. and ligamentous features. women are often thought to be more susceptible to injury than men. foot). Other primary factors include muscular development (e.5 Genetic factors in sports injury Biomechanically these encompass primary factors. Spondylolysis is present in around 6% of individuals (Pecina and Bojanic. as many of these are affected by training. muscle balance. usually of L5) in fast bowlers with such a technique (Elliott et al. and bony alignment (e. growth. it can be a debilitating injury for gymnasts. for example. The reasons given for this include the altered hip.6. sex. gymnasts. inflexibility or muscle group imbalance (MacIntyre and Lloyd-Smith.56 Injuries in sport: the body under load Obviously. fast bowlers in cricket and other athletes. Griffin (1993) pointed out that the injury rate had decreased after a more systematic incorporation of conditioning programmes into women’s sport in the 1970s. An example is the ‘mixed technique’ used by many fast bowlers in cricket. is also associated with hyperextension of the lumbar spine. 1993). women are at no greater risk than men of running injury.. 1993). the impact forces on the foot typically reach over six times body weight. and less muscle mass and greater body fat content. see Watkins (1996). The risk of further injury will be exacerbated by any failure to restore strength. At frontfoot strike. pelvis. or muscular. involving for example the foot.1 SEX. These can be mechanical. in section 2.
1993).Genetic factors in sports injury and dexterity do not appear to differ between the sexes. can mean that loads that would dislocate an adult joint will fracture a child’s epiphyseal plate. typically tenosynovitis. Such injuries can occur not only through current training and competing but also as a recurrence of injuries sustained when younger (Menard. 57 2. 1993). 1993). 1993). 1994). radius and femur are particularly vulnerable to epiphyseal plate fracture as the collateral ligaments attach to the epiphysis not the metaphysis (Meyers. heightening the risk of injury (Menard. fasciitis. in comparison with the epiphyseal plate in children. Anteversion—the angulation of the neck of the femur anterior to the long axis of the shaft and femoral condyle—greater than the normal value of 15° can also lead to injury. reducing flexibility (MacIntyre and Lloyd-Smith. In ageing athletes. bursitis and capsulitis as well as arthritis. No clear effect of age on injury rate has been established in those studies that have considered it as a primary factor (MacIntyre and Lloyd-Smith. More osteochondrotic diseases occur during periods of rapid growth in adolescence because muscle strength lags behind skeletal growth and the muscle-tendon unit is relatively shortened. 1993). In the growing athlete. 1993).5. ageing athletes have to work closer to their physiological maximum to maintain a particular standard of performance. the open epiphysis and soft articular cartilage are vulnerable. 1993). The epiphyseal plate is less resistant to torsional or shear stress than the surrounding bone. The greater strength of the joint capsule and ligaments. supporting the view that collision sports and intense training should be avoided at those times (e. Care must be taken to discriminate between the effects of ageing and physical inactivity. and this can lead to long term deformity. It is mediated through compensatory excessive pronation or supination of the foot. The greater incidence of stress fractures in the female athlete than the male athlete has been attributed to deficits in conditioning and training rather than genetics (Griffin. The distal portions of the humerus. Meyers. Because of the need to align the femoral .2 BONY ALIGNMENT Leg length discrepancy is an anatomical risk factor for overuse injury to the lower extremity. and it is strongly associated with low-back pain (MacIntyre and Lloyd-Smith. 1994). and epiphyseal plate damage can lead to growth disturbances (Meyers. often with a degenerative basis (Kannus.g. However. The occurrence of epiphyseal injury in young athletes also peaks at the rapid growth spurts. sports injuries are usually overuse rather than traumatic. The bones of children can undergo plastic deformation or bending instead of fracturing. An angle between the neck and shaft of the femur of less than the normal 125° (coxa vara) causes impaired functioning of the hip abductors because of the closeness of the ilium and greater trochanter. 1993).
peroneal muscle tendinitis and plantar fasciitis (MacIntyre and Lloyd-Smith. and tightness of the triceps surae with plantar fasciitis (MacIntyre and Lloyd-Smith. examples do exist of links between lack of flexibility and injury. It is implicated in overuse injuries such as irritation of the lateral collateral knee ligament. Pes planus is implicated in many overuse injuries. and excessive foot pronation (MacIntyre and Lloyd-Smith. 1993). 1993a). tennis players often show a reduced range of internal shoulder rotation but greater external rotation than non-players. 1993). For example. for example. However. along with increased body weight and body fat. and susceptible to excessive pronation through midstance. with a more medial centre of pressure at toe-off. may lead to an increased risk of injury. 2. muscle weakness and strenuous exercise all contribute to overuse injury (Kibler and Chandler. the neutral foot requires little muscular activity for balance.3. internal tibial torsion. excessive internal rotation at the hip. for example. iliotibial band syndrome. the positions of the muscle origins and insertions. The finding that runners who stretched were at higher risk than those that did not (Jacobs and Berson. including sacroiliac joint dysfunction. patellofemoral pain syndrome. 1993). At the knee. 1993) despite the popularity of stretching and the benefits often claimed for it. genu varum or genu valgum can lead to excessive pronation or supination depending on foot type. Inflexibility. The tendency of athletes to have tightness in muscle groups to which tensile loads are applied during their sports may predispose to injury. Pes cavus (high arched and rigid foot) leads to greater supination with a more lateral loading and centre of pressure at toe-off. stretching is often considered to be beneficial if performed properly. This relates to a development of increased internal rotator strength without a balancing strengthening of external rotators (Kibler and Chandler. pes planus. During running. genu varum.3). 1993). Despite conflicting evidence. No direct and unambiguous proof of the effects of flexibility on injury exists (MacIntyre and Lloyd-Smith.6 Fitness and training status and injury A lack of fitness. The pes planus foot is flat and flexible. 1993). 1986) should be viewed cautiously as it does not . The effects are the opposite to those of pes planus. For example. 1993). genu valgum and increased internal femoral rotation. tightness of the iliotibial band has been associated with patellofemoral pain syndrome. anteversion can cause.58 Injuries in sport: the body under load head with the acetabulum. metatarsal stress fractures. Tibial varum of more than 7° has the same effect as genu varum (MacIntyre and Lloyd-Smith. Other anatomical abnormalities can also predispose to sports injury. Shin splints are more common in athletes with pes planus (Best and Garrett. These factors can lead to an excessively loaded rearfoot valgus. and compartment syndromes (see section 2. and tarsal stress fractures.
A contralateral hamstring or quadriceps imbalance of more than 10% has also been reported to be linked to an increased injury risk (Kibler et al. may result in injury (MacIntyre and Lloyd-Smith. Ballistic stretching can be dangerous and may have reduced efficacy because of the inhibitory effects of the stretch reflex (Best and Garrett. A breakdown of the fine balance between and motor control of the hamstrings and quadriceps femoris. Attempts to assess the relative efficacy of the various types of stretching (ballistic. Also. There has been some controversy about 59 . Neuromuscular coordination is also an important factor in hamstring strains in fast running where the muscles decelerate knee extension and cause knee flexion.4. 1993). 1992). Stanish and McVicar. 1993). 1993). 1993b). for example. Many investigations of stretching have found an increase in the range of motion of the joint involved. 1992). Some evidence supports an association between lack of muscle strength and injury. such as ligaments and tendons. It may well be that the runners who stretched did so because they had been injured (Taunton. few specific studies show a reduced rate of injury with resistance training (Chandler and Kibler. the evidence is inconsistent (e. Although some research supports this. Swimmers have been reported to develop an imbalance between the lateral and medial rotators of the shoulder such that those reporting pain had a mean muscle endurance ratio of less than 0.Fitness and training status and injury imply cause and effect. flexibility. laboratory and clinical data to show that these procedures do prevent injury are lacking (Best and Garrett. Hamstring strains have been thought to be associated with an imbalance between the strength of the hamstring and quadriceps femoris muscles. the easiest way to elongate the tissues is to apply force slowly and to maintain it. 1993). Although some investigators have suggested that stretching (and warm-up) can reduce the risk of sustaining a severe injury. possibly caused by fatigue.. proprioceptive) have proved inconclusive.g. Resistance strength training has been claimed to help prevent injury by increasing both strength and. and have shown stretching and exercise programmes to prevent much of the reduction in joint range of motion with ageing (e. However. weakness of the hip abductors is a factor in iliotibial band syndrome (MacIntyre and Lloyd-Smith. 1993b). Muscle strength imbalances may arise through overtraining. 1993). while those without pain had a ratio above 0. 1993).7 (Kibler and Chandler. as in static and proprioceptive stretching (Stanish and McVicar. as rapid application of force to collagenous tissue increases its stiffness. 1993b). 1993). Hamstring strains have been reported to be more common in soccer teams that do not use special flexibility exercises for that muscle (Best and Garrett. static. 1993).. when the hamstrings have less than 60% of the strength of the quadriceps.g. possibly helping to prevent injury (Kibler and Chandler. Kibler et al. Resistance training also strengthens other tissues around a joint. when using a full range of movement and associated stretching exercises.
and how these depend on the load characteristics. 2. overtraining should be avoided as it can lead to repetitive trauma and overuse injury (Kibler et al. the effect of training errors was exacerbated by malalignment or strength-flexibility imbalances. It should also be individual and sport-specific. Furthermore. The balance of evidence fails to support the view that strength training leads to epiphyseal plate injury or joint damage. These accounted for at least 60% of running injuries.7 Summary In this chapter. 1992). leading to an increase of osteoclastic bone remodelling. The causes and relative importance of the sports injuries that affect the major joints of the lower and upper extermities. overload and adaptation. The chapter concluded with a consideration of the effects that genetic and fitness and training factors have on injury. and the back and neck were also covered. mostly through a sudden increase in mileage or too rapid a return to activity. ligaments and the muscle-tendon unit. 1993). Obviously. Meyers. 1993). The underlying mechanism has been proposed to be local muscle fatigue (Taunton. a stress fracture could occur. sudden increases in training mileage or intensity. 1993). the load and tissue characteristics involved in injury were considered along with the terminology used to describe injuries to the human musculoskeletal system. Training errors are often cited as the most frequent cause of injury. The distinction between overuse and traumatic injuries that occur to bone and soft tissues.g. Among such errors for distance runners. . including cartilage. a single severe training or competitive session. a training programme should avoid training errors by close attention to the principles of progression. decreasing the muscular function of shock absorption and causing more structural stress to the bone. with appropriate periods of rest to allow for the adaptation.60 Injuries in sport: the body under load the safety and efficacy of strength training in the prepubescent athlete (e. Training errors were also cited as the main aetiological cause of over 75% of overuse tendon injuries by Leadbetter (1993).. Taunton (1993) included: persistent highintensity training. For the 10 most common running injuries. providing the training is well supervised and maximum loads and competitive weight-lifting are avoided (Meyers. Without balancing osteoblastic activity during rest and recovery. and inadequate warm-up.
exercise and stress fractures. USA. in Sports Injuries: Basic Principles of Prevention and Care (ed. Note carefully any conflicting evidence reported. (1992) Injuries to the knee joint. and bony alignment. Note carefully any conflicting evidence reported. I. and Lindner. Describe how ligaments suffer traumatic injury and briefly outline their recovery timescale. J. elbow and arm.S. W. cartilage. muscle.10). Distinguish between traumatic and overuse injuries and provide examples of the latter for each of the tissue types in Exercise 1. Skinner. USA. tendon) explain which load types are most closely associated with injury. T. 8.J. (eds) (1996) Epidemiology of Sports Injuries. C. 10.H.10). England.Landers et al. pp. in Sports Injuries: Basic Principles of Prevention and Care (ed. London. Human Kinetics.Renström). (1993b) Warming up and cooling down. (1993a) Muscle-tendon unit injuries. (1989) Biomechanics and orthopaedic problems: a quantitative approach.References 1. J. MD. After consulting at least one of the items for further reading (section 2. Williams & Wilkins. Describe how the muscle-tendon unit suffers traumatic injury.B. IL. Williams & Wilkins. in Future Directions in Exercise and Sport Science Research (eds J. Blackwell Scientific. Best. Basmajian. age and growth.). in Exercise and Sport Sciences Reviews—Volume 25 (ed.10 ). D. England. For each main type of tissue (bone. 7.M.Holloszy). London.10). 2. 236–240. ligament.E. IL. After consulting at least one of the items for further reading (section 2. and Garrett. T. 242–251. T. 45–56. USA.D.J. knee and calf. Burr. Best.Corbin.P. prepare a synopsis of throwing injuries associated with the shoulder.8 Exercises 61 Adams.B. C. Wolfe. England. Using clearly labelled diagrams. 4. Baltimore. D. 5. 71–86. pp. After consulting at least one of the items for further reading (section 2. or ankle and foot. Champaign.F. 9. (1997) Bone. summarise the effects of the different forms of fitness training on the occurrence of sports injuries.M. USA. D. describe the various types of bone fracture and give at least one example of each in sport and exercise. pp. summarise the effects on the occurrence of injury in sport of sex. After consulting at least one of the items for further reading (section 2. prepare a synopsis of running injuries associated with the hip and pelvis. 2. or wrist and hand.G. Caine. Andriacchi. P. Caine.Reilly). 6. 171–194. Champaign.A. in Sports Fitness and Sports Injuries (ed. P. MD. 2.Renström).V (1979) Primary Anatomy.E. 3.. pp. W. and Garrett. pp. Define the three activities that are considered to relate most closely to lumbar spine injuries and outline their relative importance in at least two sporting activities of your choice.M.H.9 References . Human Kinetics. London.O. K. T.A. Baltimore. Blackwell Scientific.F.
A. T. 252–261. S J. 123–150. (1994) The Oxford Dictionary of Sports Science and Medicine. pp. 161–177. K.J. pp. in Biomechanics of Musculoskeletal Injury (eds E. (1993) Ligament biomechanics. 218–224. Chandler.J. American Journal of Sports Medicine. England. J.Grabiner). in Sports Injuries: Basic Principles of Prevention and Care (ed. Baltimore. D. W. sport and gender. Williams & Wilkins. and Hsu. Sports Exercise and Injury. P. in Current Issues in Biomechanics (ed. USA. pp.C. England. (1994) Acute ankle injuries. MD. N. Grana.M. London. Kibler. M.C. Hawkings. E.. (1986) Athletic injuries: comparison by age. 217–227.D. (1994) Chronic ankle injuries. Baltimore. (1993) Cartilage and ligament injuries. .F.H.F.Y. E. D.Gozna and I. USA. 1. pp.P. and Chandler. Blackwell Scientific. American Journal of Sports Medicine. 1–29.E. 46–62.A. Blackwell Scientific. MD. pp.F. (1995) The fast bowler in cricket: a sports medicine perspective. 194– 202.R. P. (1982) Biomechanics of joint injuries. and Kibler.M. London. P. P. R. B.D. pp. 223–241. Baltimore. USA.Renström). P.M. and Berson.A. Blackwell Scientific. 31–85. pp. I. K. Grabiner.B. Williams & Wilkins. Blackwell Scientific.Grabiner).Renström). Stockill. London. (1992) Musculoskeletal adaptations and injuries due to overtraining.C. 14. 151–155. Gozna. Kannus. (1993) Ligamentous mechanoreceptors and knee joint function: the neurosensory hypothesis. IL.R. in Clinical Practice of Sports Injury: Prevention and Care (ed. Blackwell Scientific. Kent. USA. in Biomechanics of Musculoskeletal Injury (eds E. Williams & Wilkins.F. 163–228. Williams & Wilkins. London. and Lintner. MD..J. pp.J. Oxford University Press. Evans. W. M.H. Blackwell Scientific.B. London. J. in Sports Injuries: Basic Principles of Prevention and Care (ed. 14. USA. 237–254.A. (1982) Biomechanics of spinal injury. in Clinical Practice of Sports Injury: Prevention and Care (ed. 54–70. England.O. Champaign. in Sports Injuries: Basic Principles of Prevention and Care (ed. Harrington.F. (1993) Muscle training in injury prevention. P. P.R. Champaign. Kibler. (1993) Sport specific screening and testing.B. London.A. Human Kinetics. Karlsson.S.H.F. pp.H. pp.Renström). in Sports Injuries: Basic Principles of Prevention and Care (ed.A.Renström).Harrington).. in Exercise and Sport Sciences Reviews—Volume 20 (ed. (1982) Biomechanics of long bone injuries.D. (1994) Elbow injuries. Elliott. in Sports Injuries: Basic Principles of Prevention and Care (ed.H. England. 228–245. England. B.H. MD. and Stracener.H. pp. Baltimore.Renström). 96–126. Blackwell Scientific.Renström). Chan.Holloszy).Gozna and I.A.F. T.62 Injuries in sport: the body under load Chan. A. S.J. in Current Issues in Biomechanics (ed. D. USA.Harrington). Griffin. Oxford. E. Jacobs. London. in Clinical Practice of Sports Injury: Prevention and Care (ed.R. Human Kinetics.J. Dehaven. England. pp. L. IL.Renström). England. pp.A. and Faxén.Y.C. Burnett.Harrington). W.Renström). P. and Bartlett.H.Gozna and I. England. in Biomechanics of Musculoskeletal Injury (eds E. (1986) Injuries to runners: a study of entrants to a 10 000 meter race. S. and Hsu. M. 201–206. (1993) The female athlete.F. London.M.Y. Blackwell Scientific. Chandler. W.A. K. P.F. (1993) Body composition and predisposing diseases in injury prevention. M.J. pp. England. T.
London.F. London. (1993) Overuse Injuries of the Musculoskeletal System. and Lloyd-Smith. T.W.Renström). (1994) Traumatic knee injuries. pp. Lea & Febiger. Cerullo.A. Marzo. Puddu.Renström). P.M. Blackwell Scientific. B. and Adams. in Clinical Practice of Sports Injury: Prevention and Care (ed. and Bojanic.Renström). Orava. Moore.A.J. P.F.F.Micheli). D. pp. (1994) Foot injuries. A.H. in Sports Injuries: Basic Principles of Prevention and Care (ed. London.M. P.A. USA. P.H. pp. W. Renström. (1992) Shoulder Injuries in Sport. pp.M. K. Blackwell Scientific.H. England.A. J. 63–85.B. P. in Sports Injuries: Basic Principles of Prevention and Care (ed. 246– 255. in Clinical Practice of Sports Injury: Prevention and Care (ed. pp. England. London.Williams. Mitchell. in Sports Injuries: Basic Principles of Prevention and Care (ed. USA. in Sports Injuries: Basic Principles of Prevention and Care (ed.B.Renström). P.F.A. P. England. W.A. in Sports Injuries: Basic Principles of Prevention and Care (ed. 107–119. and Hawkins. Meyers. Marone.J.F.Renström).. England.Harries. pp.H. England. London.H. London. Boca Raton. (1994) Achilles tendon injuries. Menard.Stanish and L.A. London. (ed. pp. P.Renström).Renström).H.A. P. D. and Frank. I. W. Scala. 120–134. England. London.Renström). 139–160.H. Blackwell Scientific. London.A. London. pp.H. England. Blackwell Scientific. in Clinical Practice of Sports Injury: Prevention and Care (ed. Martin Dunitz. CRC Press. (1994) Overuse knee injuries. 63 . England.F. pp. in Clinical Practice of Sports Injury: Prevention and Care (ed. London. (ed. S.A. England. 27–45. 179– 187. (1989) Kinesiology and Applied Anatomy.A. in Clinical Practice of Sports Injury: Prevention and Care (ed. England.H. P.F. (1994) The ageing athlete. C.F. London.Renström). Nigg. (1994) Shoulder injuries. P. 97–114. P.F.J. P. P. Mallon.J. pp. Pope.A.References Leadbetter. (1994) Lower leg injuries. 188–216. FL.F. England.F. in Clinical Practice of Sports Injury: Prevention and Care (ed. pp. London.J. Blackwell Scientific.H. England. J.) (1993) Sports Injuries: Basic Principles of Prevention and Care. G.Renström). Blackwell Scientific.D. 178–193. Oxford. R. Martin. England.Renström). Blackwell Scientific. London. England.F. pp.L. (1994) Hand and wrist injuries.Renström).D. London. Blackwell Scientific.H. (1993) Tendon overuse injuries: diagnosis and treatment.Renström). G. in Clinical Practice of Sports Injury: Prevention and Care (ed P. C. Philadelphia. (1993) Biomechanical response of body tissue to impact and overuse.F. pp. Oxford University Press. 144–163. Blackwell Scientific. (1993) The growing athlete. 125–143. Renström. and Beynnon.. in Clinical Practice of Sports Injury: Prevention and Care (ed. Maclntyre. B.F. 596–620.A.. B.D. (1993) Excessive loads and sports-injury mechanisms. et al.H.H.A. Blackwell Scientific. Pecina. Blackwell Scientific. R. J. pp.) (1994a) Groin and hip injuries.F. J.F. PA. Blackwell Scientific.A. M. Blackwell Scientific. (1993) Overuse running injuries. England.H. Rasch. M. P.A. Blackwell Scientific.H.F. P. 449–476. England. and Wickiewicz.H. in Oxford Textbook of Sports Medicine (eds M.
Injuries in sport: the body under load
Renström, P.A.F.H. (ed.) (1994b) Clinical Practice of Sports Injury: Prevention and Care, Blackwell Scientific, London, England. Riley, P.A. and Cunningham, P.J. (1978) The Faber Pocket Medical Dictionary, Wolfe, London, England. Rimmer, J.N. (1992) Injuries to the wrist in sports, in Sports Fitness and Sports Injuries (ed. T.Reilly), Wolfe, London, England, pp. 220–224. Stanish, W.D. and McVicar, S.F. (1993) Flexibility in injury prevention, in Sports Injuries: Basic Principles of Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 262–276. Taunton, J.E. (1993) Training errors, in Sports Injuries: Basic Principles of Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 205–212. Thompson, L. (1992) Injuries to the elbow, in Sports Fitness and Sports Injuries (ed. T.Reilly), Wolfe, London, England, pp. 216–219. Torg, J.S. (1994) Cervical spine hip injuries, in Clinical Practice of Sports Injury: Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 13–26. Troup, J.D.G. (1992) Back and neck injuries, in Sports Fitness and Sports Injuries (ed. T.Reilly), Wolfe, London, England, pp. 199–209. Tver, D.F. and Hunt, H.F. (1986) Encyclopaedic Dictionary of Sports Medicine, Chapman & Hall, London, England. van Mechelen, W. (1993) Incidence and severity of sports injuries, in Sports Injuries: Basic Principles of Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 3–15. van Mechelen, W. (1994) Head injuries, in Clinical Practice of Sports Injury: Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 3–12. Watkins, R.G. (1996) The Spine in Sports, Mosby-Year Book, St Louis, MO, USA. Williams, K.R. (1993) Biomechanics of distance running, in Current Issues in Biomechanics (ed. M.D.Grabiner), Human Kinetics, Champaign, IL, USA, pp. 3–31. Zetterberg, C. (1993) Bone injuries, in Sports Injuries: Basic Principles of Prevention and Care (ed. P.A.F.H.Renström), Blackwell Scientific, London, England, pp. 43–53.
2.10 Further reading
The two IOC Medical Commission publications below are Parts IV and V respectively of the Encyclopaedia of Sports Medicine series. They contain much useful and interesting material on sports injury from many international experts. Renström, P.A.F.H. (ed.) (1993) Sports Injuries: Basic Principles of Prevention and Care, Blackwell Scientific, London, England. Chapters 1–6, 9–15, 17–20 and 35 are particularly recommended. Renström, P.A.F.H. (ed.) (1994) Clinical Practice of Sports Injury: Prevention and Care, Blackwell Scientific, London, England. Chapters 1–16, on injuries to specific parts of the body, and 18–25 and 27–47, on specific sports, are particularly recommended. You will probably wish to be selective.
Musculoskeletal injury: definitions From Basmajian (1979), Kent (1994), Renström (1993), Renström (1994b), Riley and Cunningham (1978), Tver and Hunt (1986). Abrasion (graze): skin surface broken without a complete tear through the skin. Adhesion: bands of fibrous tissue, usually caused by inflammation. Avulsion fracture: fracture where the two halves of the bone are pulled apart. Bursitis: inflammation of a bursa. Calcification: deposit of insoluble mineral salts in tissue. Callus: material that first joins broken bones, consisting largely of connective tissue and cartilage, which later calcifies. Cancellous bone: internal material of long bone; appears trellis-like. Capsulitis: inflammation of the joint capsule. Collateral ligament: an accessory ligament that is not part of the joint capsule. Comminuted fracture: one in which the bone is broken into more than two pieces. Contusion: bruise. Cortical bone: outer layer (cortex) of bone having a compact structure. Diaphysis: the central ossification region of long bones (adjective: diaphyseal). Dislocation: complete separation of articulating bones consequent on forcing of joint beyond its maximum passive range. Epiphysis: the separately ossified ends of growing bones separated from the shaft by a cartilaginous (epiphyseal) plate. Epiphysitis: inflammation of the epiphysis. Fracture: a disruption to tissue (normally bone) integrity. In traumatic fracture a break will occur, whereas in a stress fracture the disruption is microscopic. Haemarthrosis: effusion of blood into a joint cavity. Inflammation: defensive response of tissue to injury indicated by redness, swelling, pain and warmth. Laceration: an open wound (or cut). Metaphysis: region of long bone between the epiphysis and diaphysis. Osteitis: inflammation of bone. Peritendinitis: inflammation of the tissues around a tendon (the peritendon). Rupture or tear: complete break in continuity of a soft tissue structure. Sprain: damage to a joint and associated ligaments. The three degrees of sprain involve around 25%, 50% and 75% of the tissues, respectively. Grade I sprains are mild and involve no clinical instability; grade II are moderate with some instability; and grade III are severe with easily detectable instability. There may be effusion into the joint. Strain: damage to muscle fibres. A grade I strain involves only a few fibres, and strong but painful contractions are possible. A grade II strain involves more fibres and a localised haematoma, and contractions are weak; as with grade I no fascia is damaged. Grade III strains involve a great many, or all, fibres, partial or complete fascia tearing, diffuse bleeding and disability.
Appendix 2.1 Musculoskeletal injury: some useful definitions
Injuries in sport: the body under load Subluxation: partial dislocation. Tendinitis: inflammation of a tendon. Tenosynovitis: inflammation of the synovial sheath surrounding a tendon. Valgus: abduction of the distal segment relative to the proximal one (as in genu valgum, knock-knees). Varus: adduction of the distal segment relative to the proximal one (as in genu varum, bow-legs).
The effects of sports equipment and technique on injury
The purpose of this chapter is to provide an understanding of several important biomechanical factors—sports surfaces, footwear, protective equipment and technique—that have an effect on sports injury. After reading this chapter you should be able to:
• • • • • •
list the Important characteristics of a sports surface understand how specific sports surfaces behave describe the methods used to assess sports surfaces biomechanically understand the influence that sports surfaces have on injury list the biomechanical requirements of a running shoe describe and sketch the structure of a running shoe and assess the contribution of its various parts to achieving the biomechanical requirements of the shoe • understand the influence of footwear on injury in sport and exercise, with particular reference to impact absorption and rearfoot control • appreciate the injury moderating role of other protective equipment for sport and exercise • understand the effects of technique on the occurrence of musculoskeletal injury in a variety of sports and exercises.
3.1.1 INTRODUCTION As noted in Chapter 2, much equipment incorporates materials that modify the influence of the environment on the sports performer; these include sport and exercise clothing, sports protective equipment (see Norman, 1983) and striking objects (such as rackets). The footwear-surface interface is a crucial factor in many sport and exercise injuries because it is ever-present and because
3.1 Sports surfaces
Effects of sports equipment and technique of the frequency of contact between the shoe and the surface. Changes in shoe or surface characteristics can alter not only the ground reaction force but also the activation patterns of the major leg extensor muscles (Komi and Gollhofer, 1986). Sports surfaces include gymnastics mats and snow and ice, but in this chapter we will mainly consider athletics surfaces, indoor and outdoor games surfaces and natural and artificial turf (see Appendix 3.1 for details). Many artificial sports surfaces provide properties not easily achievable from natural surfaces. However, both the mechanical properties of these surfaces, which affect their interaction with the sports performer, and their durability, need careful evaluation before they are chosen for a specific application. Surfaces have both biopositive and bionegative effects on the performer. Certain sports techniques, such as the triple somersault in gymnastics, have been made possible by the introduction of special, resilient surfaces. A change of surface may necessitate a modification of technique. The changed forces acting on the performer have altered, probably detrimentally, the incidence and type of injury (Nigg, 1986a). In different applications, performance enhancement by some surfaces will need to be weighed against injury considerations.
3.1.2 CHARACTERISTICS OF SPORTS SURFACES Sports surfaces are often complex structures with several layers, all of which contribute to the overall behaviour of the surface (see, for example, Appendix 3.1). The following characteristics are important for the behaviour of surfaces for sport and exercise and have the greatest association with injury; some other characteristics of sports surfaces that are important for their function but that have little or no direct association with injury are outlined in Appendix 3.2. Friction and traction The friction or traction force between a shoe or other object and a surface is the force component tangential to the surface. In friction, for ‘smooth’ materials, the force is generated by ‘force locking’, and the maximum friction force depends on the coefficient of sliding friction (µ) between the two materials in contact. Traction is the term used when the force is generated by interlocking of the contacting objects, such as spikes penetrating a Tartan track, known as ‘form locking’ (see also Bartlett, 1997). This friction or traction force is particularly important in, for example, running, for which the coefficient of friction or traction should exceed 1.1, and for changes of direction as in swerves and turns. For sports surfaces, the coefficient of friction or traction should be independent of temperature, weather and ageing. Friction or traction can be too high as well as too low and has an association with injury. Friction is about 10–40% greater on artificial turf than on grass. It is debatable whether
Sports surfaces spikes are necessary on a clean, dry, synthetic surface. If used, they should not excessively penetrate the surface, otherwise energy is required to withdraw the spike and damage is caused to the surface. Friction also affects the rebound and rolling characteristics of balls, such as in tennis and golf. Compliance Compliance, the inverse of stiffness, relates to the deformation of the sports surface under load and may have an optimum value for the performer (see Appendix 3.1). Although it is widely believed that stiffer surfaces can enhance performance in, for example, sprinting, training on such surfaces can increase the risk of injury owing to larger impact accelerations. A too-compliant surface, however, is tiring to run on. Compliance has no specific connection with resilience (Nigg and Yeadon, 1987). For example, a crash mat has a high compliance and low resilience, and concrete has a low compliance but high resilience. (Rebound) resilience (R) Resilience is a measure of the energy absorbed by the surface that is returned to the striking object. The resilience, or rebound resilience, is the square of the coefficient of restitution (e) between the object and surface (R=e2). For an inanimate sports object, the rebound resilience is the kinetic energy of the object after impact divided by that before impact. It relates to the viscoelastic behaviour of most surfaces for sport and exercise, where the viscous stresses are dissipated as heat, not returned to the striking object. Again, this has a relation to injury; a lack of resilience causes fatigue. Resilience is important in ball sports (ball bounce resilience) and relates to the description of a surface as fast or slow (for cricket R<7.8% is classified as slow, R>15.6% as very fast). Specified ranges of rebound resilience for some sports include (Bell et al., 1985; Sports Council, 1978 and 1984): • • • • • hockey 20–40% soccer 20–45% cricket 20–34% tennis (grass) 42% tennis (synthetic court) 60%.
Hardness Strictly, the hardness of a material is the resistance of its surface layer to penetration. This property is closely related to compliance, hard sports surfaces tend to be stiff and soft ones tend to be compliant, to such an extent that the
Effects of sports equipment and technique terms are often interchangeable in common use (e.g. Bell et al., 1985). Because of their close association with stiffness, hard surfaces are closely associated with injury (Denoth, 1986), as discussed in section 3.1.5. Force reduction This is a surface characteristic specified by the German Standards Institute (DIN). It expresses the percentage reduction of the maximum force experienced on a surface compared with that experienced on concrete; this is also called impact attenuation. Concrete is an extremely stiff surface that causes large impact forces; a surface with good force reduction will reduce this impact force, one important factor in injury (Denoth, 1986). The International Amateur Athletics Federation (IAAF) specifies a force reduction of between 35% and 50% for athletic tracks. Interestingly, the track for the Olympic Games in Atlanta in 1996 only just attained these limits with a force reduction of 36%. This was a fast track not intended for training, as the use of the stadium changed from athletics to baseball soon after the games. Force reduction is closely related to shock absorbency (Nigg and Yeadon, 1987), a term that, although frequently used, is not unambiguously defined and may be associated with the peak impact force, the force impulse or the rate of change of force (Misevich and Cavanagh, 1984).
3.1.3 SPECIFIC SPORTS SURFACES Natural surfaces These are surfaces formed by the preparation of an area of land and include turf (grass), loose mineral layers (such as cinders), ice and snow (Nigg and Yeadon, 1987). In many respects grass is the ideal sports surface. A greater attenuation of the impact force can be obtained by switching from running on asphalt to running on grass than could be achieved by any running shoe on asphalt (Nigg, 1986b). If allowed enough recovery after each use, and if properly maintained, grass has a life-span that far exceeds that of any alternative as it is a living material. Frequency of use is limited, otherwise wear damage can be considerable, and grass does not weather particularly well. Artificial surfaces These are man-made. Those that have a major polymeric component (such as artificial turf and various elastomeric surfaces) are called synthetic
Other similar devices are also used. others involve humans. and in the latter the area of deformation is larger than the impact area. validation . Kolitzus. These authors noted the size limitations for force platform testing of area elastic surfaces. drop tests similar to those above are also used. They noted that load assessment methods differ for horizontal and vertical loads and depending on whether the surface exhibits point or area elasticity. These deflection-time methods provide information about the deformation of the surface. there has been little. Tipp and Watson. Errors in drop tests because of the inertia of the surface and further errors in the use of the ‘artificial athletes’ because of the test system inertia render these methods inappropriate for such surfaces. 1982). 1985. A review of the methods of assessing how surfaces affect the loading on the body of an athlete was provided by Nigg and Yeadon (1987). 71 3. distributing the forces. the materials tests. include the use of ‘artificial athletes’ and simpler drop tests. In the former. The most important artificial surfaces are summarised in Appendix 3. For area elastic surfaces (such as sprung wooden floors). This is similar to the ground contact time that occurs for the performer in many sports. 1987). Changing the values of these may even alter which surface appears to be best (Figure 3. but the relationship between that deformation and force has not been established (Nigg and Yeadon. such as the ‘Artificial Athlete Berlin’. and reported correlations as low as 0. Vertical load assessment For assessment of vertical loads on point elastic surfaces. All drop test results also depend on the striking speed.34 between the vertical force peaks from the two.1. if any.1) is an instrumented drop test mass-spring system that produces a contact time of around 100–200 ms.2). Other methods use accelerometers or filming of markers mounted on the surface (Nigg and Yeadon.. which offer the advantage of reliability. The ‘Artificial Athlete Stuttgart’ (Figure 3.Sports surfaces surfaces. For both types of surface. Tests with human subjects usually take place with the surface mounted on a force platform. The methods should give identical results for point elastic surfaces. 1987). Furthermore. shape and dimensions of the test object. mass.1. where a weight is dropped on to the surface mounted either on a rigid base or on a force platform. 1984.4 BIOMECHANICAL ASSESSMENT OF SURFACES Various functional standards for playing surfaces have been developed (for example see: Bell et al. some tests are standard materials tests. Nigg and Yeadon (1987) provided results from a range of studies comparing subject and material tests. the deformation is only at the impact point.
72 Effects of sports equipment and technique Figure 3. All surfaces were 20–21 mm thick and impacted at 2 m·s-1 (after Nigg and Yeadon. Figure 3. radius 52. the displacement is recorded by the inductive displacement transducer (D) and the piston (P) pressure by the pressure transducer (T). surface C was best.5mm. Finally. For the 4kg shot. the electromagnet (E) has released the weight (W) which falls to strike the spring (S). surface A was best.1 ‘Artificial Athlete Stuttgart’ (after Kolitzus. which compresses in (c) as the cylinder (C) with a smooth contact area indents the surface.3kg shot. whereas for the 7. (a) Shows the position of the ‘artificial athlete’ before the start of the test on the synthetic surface.2 Maximum force determination as affected by size of object. radius 62mm. . in (d) the falling weight rises again. 1987). 1984). In (b).
Confusion can be caused by viscoelastic surfaces tending to give different results for single and repeated impacts. 1987).Sports surfaces of the use of results from materials tests as indicators of the potential of surfaces to reduce load on the human body.3). Assessment of energy loss Again.3 Representation of energy loss as the area enclosed by the hysteresis loop for a force-deformation curve (after Nigg and Yeadon. They questioned the use of rotational tests and challenged the assumption that frictional test measurements are valid in sporting activities. 73 Figure 3. a survey of the methods used to measure translational and rotational friction and some results of such tests was provided by Nigg and Yeadon (1987). they do not directly indicate the effects of these properties on the sports performer. . Horizontal load assessment For assessment of horizontal (frictional) loads on both point and area elastic surfaces. drop tests such as the ‘artificial athletes’ are used and the energy loss is calculated from a force-deformation curve (Figure 3. Although these tests provide information on the material properties of the shoe-surface interface. This led Nigg and Yeadon (1987) to conclude that materials tests cannot be used to predict aspects of loading on human subjects. and by the effect that the properties of the impact object have on the surface ranking (see above).
Although non-compliant surfaces. also supported by epidemiological studies. Further consideration of this humansurface interaction and its effect on surface compliance is provided for the example of the ‘tuned track’ in Appendix 3. Macera et al.1. the best surfaces are grass. for running. pavements and wood as the worst surfaces.1.. particularly with temperature. Kuland (1982) suggested that. Results of tests on some sports surfaces Nigg and Yeadon (1987) noted large differences in the material properties of track and field surfaces. Many types of surface are implicated in different injuries. and are involved in shin splints. As discussed in Appendix 3. are mostly implicated in injury. flatness and reasonable compliance. such that the large differences in material properties were only partly apparent from the results of subjects running on these surfaces. non-compliant surfaces are by far the worst for lower extremity injury and lower back pain. excessively compliant surfaces can lead to fatigue. Nigg (1986a) reported that impact forces are implicated in damage to cartilage and bone. smoothness. which may also predispose to injury. both for performance and for reduction of injury. This is at least partly because of changes to the subject’s movement patterns caused by changes in the surface. there appears to be an optimal compliance for a surface.1984). which increase the impact loading. Synthetic surfaces are also implicated in joint and tendon injuries owing to the stiffness of the surface. 1984). 3. that is about two to three times that of the runner (Greene and McMahon. Little correlation existed between material and subject tests. Nigg and Yeadon (1987) reported no consistency between tests with subjects and materials tests.1. Once again. Kuland (1982) identified asphalt roads. that loads on the human body are lower on surfaces that allow sliding (Stucke et al.74 Effects of sports equipment and technique Difficulties arise when using human subjects in energy loss tests because of the two distinct systems involved—human and surface—each of which can be represented as a mass-spring-damper. The important impact variables would appear to be .5 INJURY ASPECTS OF SPORTS SURFACES The footwear-surface interface is the crucial factor in lower extremity injuries. dirt paths and wood chips as they provide the desirable surface properties of resilience. The results reported by Nigg and Yeadon (1987) for tennis surfaces endorsed the view. a heel strike is far more likely on a compliant surface (54% on grass) than on a non-compliant one (23% on asphalt). For example. Hard. (1989) found the only statistically significant predictor of injury for females to be running at least two-thirds of the time on concrete.
It is. Surface stiffness is important for sports in which vertical movements 75 Figure 3. about two and a half times greater than that on a compliant surface such as grass. All of these variables are worsened by non-compliant surfaces. However. This leads to an increased demand for shock absorbency from cartilage. on compliant surfaces. on a non-compliant surface such as asphalt. 1993) as they have a greater force impulse (average force×its duration) than the impact. Hard grounds also account for an increased incidence of tendon injuries and inflammation of the calf muscles because of increased loading as the surface is less compliant.4 Loads acting on the runner: (a) important impact variables. and sometimes higher magnitude. peak vertical loading rate and the time to its occurrence (Figure 3. The peak vertical impact force and peak loading rate are likely to relate to the shock wave travelling through the body (Williams.Sports surfaces peak vertical impact force. the time to its occurrence. For example. 1992). the tendency is for a high impact peak. however. It is possible that these larger duration. .4b). leading to pain and a reduction in their shock-absorbing capacity on healing. Kuland (1982) reported that the repeated impact forces experienced when running on noncompliant surfaces may cause microfractures of subchondral bone trabeculae. and it may exceed the impact force (Figure 3. not clear which of these ground reaction force measures are most important. 1993). the active force peak tends to be about 20% larger than on non-compliant surfaces. active forces are important for injury (Williams. Hard mud-based grounds increase the likelihood of inversion injuries of the ankle joint owing to surface ruts and ridges (O’Neill. (b) vertical ground contact force for two different surfaces.4a). leading eventually to cartilage damage and arthritis.
leading to Achilles tendon. Sports shoes can change the forces in certain biological tissues by over 100% (Nigg. 1982). the quadriceps femoris. The anterior pelvic tilt and limited hip flexion increase the stress on the muscles of the lumbar spine. Downhill running requires a longer stride length. The inclination of the surface also affects the risk of injury.1 INTRODUCTION To obtain best compatibility with the human performer in sport or exercise. Artificial surfaces may reduce or eliminate sliding and impose a higher resistance to rotation. and sideways movements in jumps and shuffles (Segesser and Nigg. the incidence of injury has been reported to be at least 200% more frequent for tennis surfaces that do not allow sliding. 1982). Downhill running can also lead to lower back pain owing to posterior pelvic tilt and spinal hyperextension.76 Effects of sports equipment and technique dominate.2. 1993). which causes a greater heel strike impact force and imposes greater strain on the anterior muscles of the thigh. two additional movements have to be allowed for: rotations. such as clay and a synthetic sand (Nigg. 3. ideally. the injury aspect of the latter will be covered later. . the increased pressure can lead to chondromalacia patellae. Also. ankle and knee joint injury (McDermott and Reilly. these are exacerbated by banked tracks. Uphill running imposes greater stress on the patellar ligament and quadriceps femoris tendon and on the ankle plantar flexors at push-off. In soccer. which can lead to lower back pain (Kuland. presses the patella against the articular cartilage of the femur (Kuland. contracting eccentrically to decelerate the thigh. as the foot has to be lifted to clear the ground. 1993). A severe camber on tracks and roads increases the pronation of the outside foot and increases the load on the inside leg. 1993). Sliding allows a reduction in loading because of the increased deceleration distance. as the firm sand near the sea is also ‘cambered’. be designed for specific sports and exercises and for the relevant surface qualities. leading to a more forceful heel strike and greater stress on the lateral aspect of the foot. this can also occur when running on beaches. For example. 1993).2 Footwear: biomechanics and injury aspects 3. Running on flat turns causes adduction of the inside hip and increased foot pronation. The stride length of the outside leg increases. such as asphalt and synthetics. the frictional behaviour of the surface is of great importance when large horizontal movements occur (Nigg. shoes should. in ball games compared with running. sliding tackles on artificial surfaces can lead to severe friction burns to the thigh and elsewhere. 1992). For example. than for those that do. The frictional behaviour of the surface is also important in the increased frequency of injury on artificial compared with natural turf.
impact attenuation and rearfoot control. This section will concentrate on the latter.2. a foam layer provides good perspiration absorption and a comfortable feel. soccer and several other sports. 3. A conflict often exists between what might be considered the two most important biomechanical functions of a running shoe.2 BIOMECHANICAL REQUIREMENTS OF A RUNNING SHOE A running shoe should provide the following (for example: Cavanagh. 1986. Uppers A compound structure is the most common. 77 3. Hauser and Schaff (1990).5) for the above requirements are considered in the following sections. . Frederick.Footwear: biomechanics and injury aspects Advances in the design of such shoes have occurred in recent years. running shoes appear in general to lose around 30% of their impact attenuation properties after a modest mileage. Injury aspects of the ski boot are covered by. where both material and constructional aspects are covered. for example. woven nylon taffeta supplies most of the strength. Furthermore. 1980. Other chapters in Segesser and Pförringer (1990) deal with injury aspects of footwear used in tennis. Nigg.3 THE STRUCTURE OF A RUNNING SHOE The most important parts of a typical running shoe (Figure 3. which are widely used in sport and exercise. Usually. while a cotton weave backing helps to prevent the nylon from tearing or snagging. 1986a): • • • • • • • attenuation of the repetitive impact forces maintenance of foot stability (rearfoot control) with no exacerbation of movement at the subtalar joint (supination-pronation) friction-traction at the shoe-surface interface allowance for different footstrike pressure distributions no exacerbation of any structural irregularities of the arches of the foot dissipation of heat generated.2. particularly when the shoe incorporates synthetic materials and artificial surfaces are involved comfort for the wearer. The wrong footwear is a major factor in causing running injury. particularly for ski boots and running shoes. the use of a good running shoe is one of the best ways such injuries can be avoided.
but all foams form a ‘compression set’—a permanent deformation—because of repetitive stress. (1985) found a loss of about 30% of shock absorbency across a wide range of top class running shoes after only 500 miles (800km) of running.78 Effects of sports equipment and technique Figure 3.5 Parts of a typical running shoe (reproduced from Nigg. with permission). The long-term durability of these foams is unknown. Cook et al. 1985) (Figure 3. in which other . These foams are 80% gaseous with thin (<10µm) walls. Closedcell foams regain their original dimensions more quickly than open-cell foam. although the shoes may otherwise look as good as new. the claims for which have not always been substantiated by rigorous scientific research. More recent developments have included various pneumatic and liquidfilled devices. 1986d. 1993). Midsoles of polyurethane foam.6). This occurs through fracturing and buckling of the cell walls of the foam material (for example Parry. Midsoles and wedges These are the critical parts of the shoes for shock absorption. This absorbs energy mainly by compression of the pockets of air entrapped in the cells and secondarily by deformation of the cell walls. This reduces the ability of the material to absorb energy substantially. the most commonly used material being a closed-cell polymeric foam (EVA—ethylene vinyl acetate) (Easterling.
have also been developed. for example. The whole concept of energy return has. Easterling. (c) heel at 701 miles (1122km) (×1200). (b) forefoot at 2000 miles (3200km) (×12). however. Segesser and Nigg (1993). materials are encapsulated.g. 1993). (d) heel at 2000 miles (3200km) (×600) (from Parry.Footwear: biomechanics and injury aspects 79 Figure 3. been questioned by. These have been claimed to give good cushioning and energy of rebound (e. 1985). .6 Scanning electron micrographs of EVA midsoles: (a) forefoot at 0 miles (0km) (×12 magnification).
this should help to reduce impact shock. Insole board Some shoe designs. In modern running shoes a fibre-board. see section 3. . known as ‘board-lasted’ shoes.2. External counter stabilisers are also used to reduce excessive rearfoot movement (Easterling. incorporate an insole board that provides the rigid base for the rest of the shoe and gives excellent stability but limited flexibility. Combination-lasted shoes have the rear part of the shoe board-lasted and the forefoot part slip-lasted: this represents a good compromise between rearfoot stability and shoe flexibility (Easterling. 1993). known as ‘slip-lasted’ shoes. is usual.6 for further consideration of rearfoot control in running shoes. therefore. 1993). Insole (or sockliner) Usually made from a moulded polyethylene foam with a laminated fabric cover. do not have an insole board and the upper is fitted directly to the last giving flexibility but with limited stability. Heel counter This is an important part of the shoe as it contributes to shoe and rearfoot stability. 1996). and changes in tread configuration can affect both the shock attenuation and traction. 1993). Other shoes. composed of cellulose fibres embedded in an elastomeric matrix with additives to prevent fungal and bacterial growths.80 Effects of sports equipment and technique Outsoles Polyurethane rubbers are generally used here because of their durability and abrasion resistance. absorb perspiration and provide comfort. The design of the heel counter has a profound effect on the stiffness of the fatty heel pad and. cradling the calcaneus and limiting excessive pronation. Treading removes to some extent the poor traction of polyurethane soles when wet. Rigid. EVA compounds fail on the last property. The nearby ‘Achilles tendon protector’ (or heel tab) is somewhat misnamed—hard or high heel tabs can cause inflammation of the tendon or peritendon (Dunning. It should provide good friction with the foot or sock to prevent sliding and consequent blistering (Easterling. durable materials are needed for this purpose and a sheet of thermoplastic is normally incorporated in the heel counter. wearing through in 200 miles (320 km). on impact attenuation.
Footwear: biomechanics and injury aspects Inserts A wide variety of ‘inserts’ is available. Abrupt changes in velocity—acceleration.2. Many other injury risks are associated with poor or inappropriate footwear. 1994). can anchor the knee and ankle joints in tackles or swerves.. A common cause of injury is insufficient rotational freedom between the surface and footwear.1. In rugby and soccer.g. Orthotic devices are inserted into footwear specifically to align or correct the function of parts of the body (Craton and McKenzie. in a similar way. have been associated with the use of resin on basketball shoes (Wilkinson. Moore and Frank. a viscoelastic material. modern boots and studs can cause injury. the foot remains fixed to the ground while the trunk rotates. 1992). 1994). Wet and muddy surfaces reduce such injuries as they allow free stud movement and therefore rotation of the lower leg (Hardiker et al. 81 3.. avulsion fractures of the lateral malleolus are then possible. 1993) and these will be considered in section 3.4 FOOTWEAR AND INJURY As noted in section 3. 1989) and other sports (e. supposedly. deceleration. reduces the skeletal accelerations associated with repeated impacts. including foam rubbers with few air cells to reduce compression set. . either loosely or glued in position. Various materials are used. although providing more traction. Modern studs. twisting—are common in sport and exercise and put great stress on ankles and knees in particular.g. Both footwear and surfaces are implicated. Other investigators have suggested that inserts do no more than provide a tight fit.3. usually in the plantar flexed and inverted position and affecting the anterior talofibular ligament. Stüssi et al. soccer and other sports. Wet circles or poorly gripping footwear can cause loss of balance. changes in direction. Certainly they should not raise the heel of the foot so much that rearfoot control is hindered because of an increased lever arm of the ground contact force. 1992). this assists rapid stopping but also increases frictional loading in other directions. is popular and. As well as ankle and knee sprains. However. others can be added. One of the most common knee injuries is caused when changing direction in basketball.3. Ankle sprains. Sorbothane. in twisting and turning injuries in racket (e. In violent twisting or turning movements. as in some tackles and swerves. usually the anterior cruciate ligament (Moore and Frank. the shoe-surface interface is a crucial factor in lower extremity injuries. the low cut of most modern boots provides little stability for the ankle joint. Some may be built into the shoe. a combination of valgus and external rotation loading damages one or more of the knee ligaments. James and Jones (1990) considered training errors to be the most important cause of injury in distance runners.
contributory factors. Shin splints involve inflammation of the periosteum (periostitis). soft materials give good cushioning but promote rearfoot instability. 1982). muscle sheath (myositis) or tendon (tendinitis).82 Effects of sports equipment and technique leading to muscle tears in the lower limbs in shot-put (Reilly. A runner experiences between 500 and 1200 impacts per kilometer. the time to reach the peak . as in gymnastics (Kuland. this can be prevented by moulded heel pads. with peak impact forces of several times body weight. and discus and hammer-throwing. An increased training load. 1989). Flat-heeled sports shoes can cause knee injury by permitting too much ankle dorsiflexion and tightening the gastrocnemius. A thin. Friction in ill-fitting footwear can cause blisters. which enable the body’s own heel fat pad to cushion effectively. Use of lightweight shoes in relatively high impact loading can cause excessive pronation leading to midtarsal joint synovitis. noting that most injuries in distance running involved overuse. 1984).5 IMPACT AND THE RUNNING SHOE Misevich and Cavanagh (1984) considered the basic injury risk in running shoes to be impact. Pecina and Bojanic. the peak magnitude of the impact force. therefore. Poor footwear and hard surfaces can lead to heel bruising. as in the high jump. typically in the cortex about 6 cm above the tip of the lateral malleolus or through the posteromedial tibial cortex. Medial shin splints are associated with excessive pronation and are. 1992). suggested that running shoes should not only provide shock absorption but should also control movement of the foot. shin splints and Achilles bursitis. Achilles tendinitis can be caused by a change from training shoes to lowheeled running shoes. the peak loading rate (associated with muscle stretching velocities). Norman (1983). therefore. which forces the osteoclasts and osteoblasts to alter bone structure. change of surface or footwear may be implicated in the increased loading (e. unpadded shoe counter can cause subcutaneous bursitis (behind the inferior half of the Achilles tendon). 1982). 1993). 3. Overuse injuries can result from accumulated impact loads. The action of osteoclasts may be rapid enough to cause a defect leading to loss of bone continuity. exacerbated by running on cambered surfaces (Kuland. Rigid shoes and non-compliant surfaces. As noted above. as well as uphill running. cushioned heel.g. Achilles tendinitis can also arise from an asymmetrical pull on the tendon caused by a heel counter that is too soft or distorted (Becker. leading to overstretching of the tendon under load (Curwin and Stanish. Anterior shin splints are caused by stress in the tibialis anterior dorsiflexing and stabilising. this can be reduced by the use of a heel pad or a wider. Stress fractures occur as an adaptation to training stress.2. Frederick (1989) made clear the dichotomy between these two requirements. and include stress fractures. can cause increased loading on this muscle and are. for example.
This mechanism is not available to rearfoot strikers. The rigidity of the pes cavus foot requires an effective shock absorbing midsole. 1989).Footwear: biomechanics and injury aspects impact force and the time to reach the peak loading rate are all considered to relate to injury. .7 Vertical ground contact force in two running styles. allows a prolonged period of force dissipation. 1993). 1989). this group predominates in distance running because of the faster fatigue of the plantar flexors in forefoot running (Pratt. The typical vertical force-time curves for heel-toe running on compliant and non-compliant surfaces have important similarities and differences 83 Figure 3. The latter are able to use the eccentrically contracting plantar flexors to prevent heel strike and absorb shock. and the heel fat pad can maintain its capacity to absorb shock over many impacts (Pratt. The adult femur can lose 10mm length after impact because of bowing and elastic deformation. This is one example of the body’s own shock attenuating mechanisms. and shoes designed for this foot type normally have a narrow heel width with minimum flare (Craton and McKenzie. The control of the lowering of the rest of the foot. Cancellous bone is able to absorb shock although cartilage seems to play little role in this respect. which are both active (through muscle tone and proprioceptive information about joint position) and passive (through the elasticity of bone and soft tissues). because of more joints in the kinetic chain.7). Peak impact forces are greater for rearfoot than for midfoot and forefoot strikers (Figure 3. As noted in Chapter 1. the arches are important to the shock absorbing properties of the normal foot.
g. If the material of the surface or shoe is thick enough. Tibia decelerations are affected by shoes. 10% sockliner. 60% midsole-wedge. The probability of heel strike. then it will not provide enough shock absorbency. If the shoe is too hard. Such adaptations can lead to smaller measured differences in ground contact forces than in the shoe’s material properties. Manufacturers have tended to pay more attention to shock absorbency. For these surfaces. The energy absorption by the shoe (rather than that absorbed by the foot and lower limb) can be partitioned between the various parts of the shoe to which impact energy is transferred up to the time of the impact peak: 20% outsole.g. The hardness. active force peaks are almost identical for barefoot and shod running. and relates to running speed. reduces rearfoot control. This has resulted in many innovations including . Some evidence shows that the use of shock absorbing materials in shoes can reduce injury. The remainder of the force-time trace is an active propulsion force of low frequency (<30 Hz). than to rearfoot control in designing running shoes. with runners responding to the physical characteristics of the shoe.. This is perhaps because too much shock absorbency slows the runner down. It has been reported (Nigg et al. it is dependent on the characteristics of the shoe on synthetic surfaces. the rest is downgraded to heat energy. The body’s passive mechanisms are important in attenuating higher frequency components and the active ones are more important at low frequencies. a material with a Shore hardness of 35 or more is to be preferred (e. 7 g barefoot. However. However. 3% insole board. The peak impact force occurs after about 20– 30 ms and the propulsive peak after about 100 ms. To prevent this. soles that are too soft can ‘bottom out’..84 Effects of sports equipment and technique (Figure 3. of running shoes can influence aspects of technique. the amplitude of the impact deceleration of the heel is independent of the shoe worn on grass. owing to thickness limitations. McLellan (1984) reported. for example. then the impact peak will be reduced if the materials are soft. for walking.4b). leading to an increase in the impact force. Nigg et al. 2% sock (Misevich and Cavanagh. 1986).. 2. for example.5–4 g with an 18 mm soft crepe rubber sole and less than 2. for heel-toe running at 4 m·s-1. yet many runners prefer uncushioned shoes for racing. even the softest shoe gave an amplitude that was 45% greater than that on grass. However. and distorts feedback mechanisms (Pratt. Some of this is stored elastically and recovered.5 g with a 6 mm modified polyurethane insert in a hardsoled shoe. The impact speed of the foot is the greatest influence on the magnitude of the peak impact force. Nigg et al. 1986). 1984). 1986) that. The initial impact is a high frequency force (>30 Hz) not consciously affected by the runner owing to the 30 ms muscle latency period. with much attention to midsole hardness. 1989). or cushioning. has been reported to decrease as the force of impact increases through reduced surface compliance or increased running speed (e.
knee flexion. unlocks this joint and increases the flexibility of the foot. However. Claims have been made for running shoes. typically lasting until midstance. Craton and McKenzie.g. several pieces of research have shown only a slight relationship between peak vertical impact forces and midsole hardness. Nigg and Cole (1991) reported results from tests with seven subjects and three different running shoes differing only in midsole hardness. In running. therefore. gels. and. injury reduction. hydroflow and other devices. The propulsive phase involves the foot returning to a supinated position as the hip and knee extend. All their results showed little effect of midsole hardness. this helps to dissipate energy. Segesser and Nigg (1993) noted that.. aiding shock absorbency and compensating for foot abnormalities. stress fractures and shin splints. for example through minimising the weight of the shoe. 1984).6 RUNNING SHOES AND REARFOOT CONTROL Rearfoot control involves the shoe’s ability to limit the amount and rate of subtalar joint pronation immediately after foot strike on the lateral border (Clarke et al. and greater internal forces during the propulsive phase than during the impact phase. it produces an increased medial rotation of the tibia. If pronation is excessive. this is transferred along the kinetic chain causing greater loading on many tissues of both the leg and lumbar spine (e. Pronation. With no shoes the pronation phase is longer and slower and the take-off and contact are made with less supination. despite evidence and speculation linking impact loading to cartilage degeneration. but may be important for comfort or for fine tuning of muscle-tendon units. medial rotation of the femur and hip flexion. Using an EMED pressure insole and a six-segment foot model. Segesser and Nigg (1993) concluded that energy conservation. or prolonged into the propulsive phase. they calculated internal bone-on-bone contact forces and tendon forces. the femur laterally rotates and the ankle plantar flexes.Footwear: biomechanics and injury aspects air filled chambers. had a valuable role to play. Reviewing this topic. they dismissed the concept of energy return in sports shoe construction. providing a return of only 1% of the total energy needed for each stride. as the energy stored during landing cannot be returned at the correct time. no prospective study existed that analysed the link between the aetiology of sports injury and external or internal impact forces. The shoe sole does not have the spring properties needed to achieve such energy return. relating to the performanceenhancing role of energy conservation and energy return. Because of the . contact is usually made on the lateral border with the foot supinated and with the midtarsal joint locked. 85 3. However. This pronation is accompanied by ankle dorsiflexion. location or frequency. The authors proposed that the cushioning properties of the running shoe are not important for the loading within the foot. 1993).2.
1993). 1993).8) between the forces acting on the shoe and the joints of the body. owing to the increased moment arm for the impact force occurring on first contact with the outer border of the shoes (see Figure 3. tendons and muscles. Enhanced torsional stability around the longitudinal axis of the shoe can also be achieved by the use of firm materials placed between the upper and midsole.g. be the cause of lower extremity pain in many runners.8). indeed. If the force (F) remained the same. Thick-soled shoes with broad-flared heels and wedged midsoles can protect the Achilles tendon from injuries caused by large impact forces in many runners. along with the establishment of the relationship between lower extremity structure and pronation. Indeed. Shoe designs that increase the lever arms between the joints and the ground will generally reduce impact forces but increase pronation or supination (Nigg. For example.86 Effects of sports equipment and technique increased loads involved. including lateral compartment syndrome of the knee. However. Shoe design changes can influence the lever. which is reinforced with a higher density material. Evidence is lacking to indicate how much reduction in overpronation is needed to relieve symptoms and it has not been demonstrated that appropriate footwear will remove symptoms (Williams. 1993). thick and soft shoe soles would appear to give best impact attenuation. Nigg (1986c) also noted that shoes can increase oversupination before take-off compared with barefoot running. a technique known as board-lasting (Craton and McKenzie. it may. or moment. Rearfoot control in sports footwear owes much to thermoplastic heel counters that stabilise the subtalar joint and limit excessive pronation. Nigg. further understanding of the mechanism of injury involving excessive or rapid pronation is needed. . 1986). such soles would hinder rearfoot control. However. the moment about the foot’s long axis would also increase. Achilles tendinitis and posterior tibial tendinitis (e. a reduction of the flare of the midsole on the lateral aspect of the heel can obviously decrease the moment about the subtalar joint (Stacoff and Luethi.or three-fold. To obtain a compromise between impact attenuation and rearfoot control. As overpronation damages ligaments. Pratt (1989) reported that the heel base should not be wider than 75 mm to prevent too rapid pronation and that bevelling the lateral border would also be beneficial. arms (as in Figure 3. the more sideways-directed angle of the Achilles tendon can cause injuries to that tendon and to the insertion tendon of the tibialis anterior.8 Schematic representation of how the moment arm (r) in (a) might be increased by a change in the heel flare (b) or thickness (c). The use of a straight last. overpronation has been heavily implicated in a wide range of injuries. Shoes with inappropriate heel flare can increase pronation or supination two. by generating excessive moments in the leg and ankle. the material of the lateral side of the midsole. sports shoes should seek to reduce this risk. which absorbs shock. because of greater mediolateral forces and bending moments (Nigg. is often softer than that used on the medial side. 1993). and can change the way in which external forces affect internal forces. 1986a). iliotibial band syndrome. therefore controlling excessive pronation. This reduces any tendency for the shoe to collapse on the medial side. rather than the Figure 3.
Examining various running shoes. 1993).Other equipment and injury earlier curved last (Figure 3. Also. Shoes for the rigid foot (pes cavus) often incorporate features to enhance rearfoot motion. these induce a change of movement (Segesser and Nigg.9% by body contact. 77% of injuries are caused by implement impact as against 3. Such features include the use of a curved last to increase the pronation of the foot. 87 Figure 3. many claims have been made for injury reduction by. sports and exercise equipment can have either bionegative (increase of injury) or biopositive (decreasing injury) effects. protective equipment. Many other strategies have been used to affect rearfoot movement.9). Nigg et al. as well as features to reduce injury. rigid irregularities on the insole. and slip-lasting to decrease the torsional rigidity of the shoe by having the upper sown directly into the midsole without any intervening stabilising material (Craton and McKenzie. Protective equipment should reduce the risk of injury but not create another hazard. The evaluation of sports protective equipment should relate to its protective 3. for example. such as through a change of tactics or training. In hockey. (1986) noted that many medial supports were too far towards the forefoot to affect initial pronation and had no effect on total pronation wherever they were placed. or detract from the sporting activity. (b) straight. by altering the sensory input. As was noted earlier.3 Other sports and exercise equipment and injury . 1993). Norman (1983) warned that much protective equipment is designed on an ad hoc basis and that some doubt exists about how much protection is provided. However. 1993). Better results might be achieved by putting small. also helps to reduce pronation (Craton and McKenzie. for example.9 Running shoe lasts: (a) curved.
Objective assessment of head and neck protective equipment needs to account for whether the impact threatens blunt trauma. the risk is being struck by a high velocity object. 3. or concentrated trauma. improvements . the liner can bottom. Sports headgear usually incorporates a firm outer shell to distribute impact over a large area and a liner that absorbs the energy of the blow. Plastic covered eye protectors have helped to reduce eye injuries in squash. Here. In rugby. In the latter. Few protective devices for sport have been evaluated in this way (Bishop. one example being neck injury to a head tackier in American football. information is lacking about protective headgear in most of these sports. and reduced concussion by attenuating the transmission of a blow through the temporomandibular joints. skiing and mountaineering. addition of a vertical bar has reduced facial injury.88 Effects of sports equipment and technique role and how it reduces or distributes the applied load. Protective equipment should reflect the type and magnitude of loading in sports such as lacrosse.3. In lacrosse. Test protocols are more developed for the former trauma than the latter. these generally include the magnitude and duration of the acceleration of the head. as in cycling and skiing. Injuries can also occur from the use of protective equipment. Several indices of impact severity have been proposed (Bishop. much energy is needed to crush these. cricket.1 THE HEAD AND NECK Many head injuries in sport are caused by direct impact or the whiplash effects of torso acceleration (Norman. the liners are medium-density resilient foams. its performance should be judged against tissue tolerance criteria. For protection against multiple concentrated traumas. field hockey. such as an ice hockey puck. If the foam is too soft. as when a cyclist’s head hits the ground.g. they have also reduced both the incidence and the severity of facial fracture. The effects of cricket head protectors on injury require careful assessment as their use has undoubtedly encouraged both batsmen and close fielders to take greater risks. There also seems to be a conflict in the literature concerning the desirable features of protective headgear and how to assess the injury potential of impact loads. van Mechelen. Unfortunately. 1993). causing the force to be transmitted to the skull (Bishop. the old style mask lacked a vertical bar so that the ball or stick could penetrate. 1993) but they are not universally accepted (e. 1994). as in ice hockey and lacrosse. Some evidence shows that protective equipment has reduced injuries to the head. gum shields have not only provided protection to the teeth. 1993). 1983). For lower energies. stiff high-density non-rebound liners are used. the impact can be transferred to the skull. In squash. whereas open protectors have no positive effect. For blunt-trauma protection from a single impact. 70% of eye injuries are caused by the ball and 86% of eye injuries in badminton are caused by the shuttle.
where the grip is smaller than that in tennis. as in the fortunately rare spiral fracture of the humerus mentioned in Chapter 1. These neck injuries were reduced dramatically by the introduction of a rule change in 1976 banning the use of the head as the first point of contact in tackling and blocking (J∅rgensen. Nirschl and Sobel. This view agrees with the research of Hatze (1976). As an example. increased injury potential exists because of the addition of an extra segment to the usual kinetic chain. 89 3. the distance from this crease to the tip of the middle finger of the extended hand is the recommended grip circumference (e. for club players and learners. who proposed that a player’s inability to find the ‘sweet spot’ tends to lead to a compensatory tightening of the grip.3. In racket and other sports. this can involve acute injury. tennis elbow is more likely to be caused by excessive string tension. based on the anthropometric palm crease factor. 1982) have variously: • • • • • • • • blamed head-heavy rackets thought that a change from light to heavy rackets was the cause blamed the change from a wood to a steel racket reported more symptoms in players using wooden rackets (if there were no technique differences) thought that the racket was irrelevant blamed excessive string tension for elbow injury suggested a lower incidence of tennis elbow using gut strings considered the size of the ‘sweet spot’ to be important. 1994). Most injuries to the upper extremity in sport are overuse injuries caused by repeated loading of the tissues affected. poor technique is the major factor (e.g. Some authors (for example Chan and Hsu. Curwin and Stanish. 1984.g Curwin and Stanish. For good players. which increases the vibrations transmitted to the elbow. the grip size is easily adjusted to the so-called optimal size. .2 THE UPPER EXTREMITY Falls directly on the shoulder have a far greater injury risk if the surface is hard. 1994. 1984). 1994. In tennis. 1993). Many researchers think that. The grip size may be more important in badminton and squash.Other equipment and injury in the protective capabilities of modern helmets led to a reduction in head injuries but a 200% increase in fractures. Chan and Hsu (1994) supported the view that vibrations transmitted from too tightly-strung a racket are implicated along with too small a grip or offcentre hits. repeated loading and some powerful mishits. it is instructive to look at the link between tennis elbow and the racket used. dislocations and subluxations of the cervical spine from the mid 1960s to the mid-1970s (Torg. Kuland. for example in rugby.
3. They emphasised the need for individual prescription to suit the wearer’s biomechanics. knee braces could provide only limited protection against valgus injuries and should not be routinely prescribed to athletes. the risk of injury. see Craton and McKenzie (1993) or Hunter et al. none of seven functional knee braces was found to provide a strain-shielding effect for the anterior cruciate ligament for a shear force of 180 N (Pope and Beynnon. Craton and McKenzie (1993) cautioned against the use of prefabricated orthotics. are preferred. 1982) have considered that the fitting of orthotic devices has become too indiscriminate. these authors drew the following conclusions. 1993). Some disputes have arisen about the use of equipment such as knee braces for prevention and rehabilitation from injury.2). Some authors (such as Kuland. Foot orthotics are normally used to: minimise overpronation or oversupination. extending under the entire foot. The lower general incidence of upper extremity injuries in badminton compared with tennis and squash is mainly due to the lightness of both the implement and the object struck. Reviewing the evidence of the role of prophylactic knee and ankle braces. soft orthotics. dissipate the energy of foot strike.3 THE LOWER EXTREMITY The shoe-surface interface is the crucial factor here (covered in sections 3. and the sports involved. more investigations were required before universal use of prophylactic ankle supports could be recommended. They further considered that most athletic footwear in the 1990s is designed to address most moderate biomechanical abnormalities and is effective in reducing lower extremity overuse injuries.3. For shock absorption. 1993). and treat specific biomechanical abnormalities. It has become common for injured runners to have orthotic devices fitted to compensate for anatomic abnormalities. (1995). Although some studies have proposed that prophylactic athletic tape may play a role in decreasing the incidence of injury. Secondly. made of flexible plastics. Pinkowski and Paulos (1993) reported that some knee braces increased the forces transmitted to the knee and. Based on their review. (1993) questioned its efficacy. are usual (Craton and McKenzie. For rearfoot control. 1992). the grip is smaller. including foot type. including the risk of lateral ankle sprain. does not account for runners’ technique adaptations and may exacerbate injury. similar to that occurring in moderate sporting activities. Lutz et al. therefore. In badminton and squash.1 and 3. For example.90 Effects of sports equipment and technique Polich. They considered it to be no substitute for the proper conditioning . usually extending from the posterior aspect of the calcaneus to the mid-portion of the metatarsals. For consideration of the last of these. First. no similar optimal formula has yet been agreed for these sports (Sanderson. semi-rigid orthotics. 1996).
These injuries have been virtually eliminated by the use of higher. The use of an incorrect technique is usually considered to exacerbate the injury potential of sports. The sport and exercise scientist should seek to identify incorrect techniques to prevent injury. However.4. 91 3. Other external rotation injuries owing to fixing of the ski formerly included ankle fractures. 3. Imperfections remain in some ski release bindings and the need still exists to reduce serious knee injuries in Alpine skiing (Johnson and Incavo.4 Musculoskeletal injury—technique aspects 3. The use of many repetitions of these techniques in training should not therefore be undertaken lightly. 1990). an increase in anterior cruciate ligament sprains appears to be associated with today’s higher and stiffer boots (Johnson and Incavo.3. although indirect evidence can often be deduced (Mallon and Hawkins. the risk of injury may well override beneficial motor learning considerations. The techniques used. lower extremity equipment-related injuries have declined over the past three decades owing to improvements in ski release bindings. when low ski boots were common.Musculoskeletal injury—technique aspects and strengthening required for athletic competition. The most common downhill skiing injury to the knee is a grade 1 medial collateral ligament sprain caused by the inside edge of the ski catching in the snow and externally rotating the leg forcing the knee into valgus. 1990). The design of ski release bindings has evolved to try to prevent injury while not releasing under ‘safe’ loads.4 ALPINE SKIING: RELEASE BINDINGS The injury potential posed by the ski has long been recognised. 1994). stiffer moulded boots. usually caused by release bindings failing to release. They further reported the importance of the tape strength. loading the inner edge of the lower ski. 1990). The usual two-mode release bindings (which release under twist at the toe and forward lean at the heel) are not sensitive to some types of load (Johnson and Incavo. Higher boots have also reduced the incidence of ruptures of the peroneal retinaculum formerly caused by forward falls. with a value of at least 139 N (the ultimate strength of the anterior talofibular ligament) being needed to protect against ankle inversion injury. may therefore cause injury. Training to improve technique and acquire appropriate strength and flexibility is likely to help to reduce injury .1 INTRODUCTION Sport and exercise participants subject their bodies to loads that are well beyond the stresses and strains of sedentary life. However. These boots have led instead to more spiral fractures of the distal third of the tibia and fibula. This has rarely been verified scientifically. even when considered ‘correct’.
be discussed in this chapter. 3. Damage to the transverse abdominal muscle can result from errors in timing the hip ‘lead’ over the shoulders in the hammer throw (Reilly. biceps curls involving spinal hyperextension. Soft tissue injury and avulsion fractures have been reported in the shot-put from incorrect timing of the contractions of back muscles (e. Weight training techniques can also cause spinal injury. Sudden changes from trunk flexion to extension (or vice versa) combined with torsion may injure the dorsal spinal ligaments in recovery shots in racket sports. and lumbar spine injuries in fast bowlers in cricket were touched on in Chapter 1. The weight is kept close to the body as the lift is made with knee then hip extension. for example. have changed from high-to low-impact to reduce the incidence of injury. This technique should be used for lifting any weight from the ground. The incidence of spondylolysis (stress fracture of one or both neural arches) and other lumbar abnormalities in fast bowlers is a good example of the association between technique and injury. techniques in many sports are determined by the activity. such as aerobics. These may occur in a rugby scrum collapsing and wheeling.4. These include: bent rowing with knees fully extended. 1993). The ‘Olympic lifts’ both involve two phases in which the large muscles of the legs are used to lift the weights with an intermediate. The technique usually recommended is the ‘knee lift’ technique where the athlete looks straight ahead with a straight back and knees initially flexed. The major factor appears to be the use of the ‘mixed technique’. 1992). 1992). Some exercise activities. Low-back pain. nor will most aspects of strength and flexibility training. sit-ups with feet fixed (which recruits the hip flexors). In this. Reilly.g.2 THE HEAD AND TRUNK Weight-lifting activities can impose unacceptable loads on the spine. particularly at high standards of performance (Nigg. Some injuries (such as gouging in rugby) are caused by illegal technique and will not. and to a minor extent in soccer heading. The following provides an overview of the relationship between technique and injury using selected examples. positioning phase to enable the second lifting phase to occur. the bowler counter-rotates the shoulders away from the . generally. its causative factors. Combined bending and torsion loads can cause injury. or fully extended knees (passive tension in the posterior thigh muscles). reducing possible changes to technique. Several activities should be avoided because of high loads on the lumber intervertebral discs already forced into an abnormal curvature. particularly if performed incorrectly.92 Effects of sports equipment and technique as well as to improve performance. However.
The only significant difference was that between group 1 and the other two groups for the change in shoulder alignment from backfoot impact to the minimum angle. disc degeneration or bulging on MRI scan. However.. Elliott et al.. by players learning the correct tumbling techniques of falling and rolling. Team sports Bad falling techniques. and a straight front knee from frontfoot impact to ball release (see also Bartlett et al. A relatively low incidence of spondylolysis has been reported amongst genuine side-on or front-on bowlers. It might be hypothesised that overcoaching in early years has been inappropriate. the front-on technique may be more natural. 3. to a more side-on position at frontfoot strike (Figure 3. lack of physical conditioning. In rugby. Other factors that may contribute to lower back injury in fast bowlers include: overbowling. can cause the range of injuries discussed in Chapter 2.9 years) grouped the bowlers into those showing: 1 2 3 no abnormal radiological features. poor hamstring and lower back flexibility. spondylolisthesis (forward subluxation of one vertebral body on another. poor footwear and hard surfaces.4.. particularly in indoor nets.10).Musculoskeletal injury—technique aspects hips. British coaches and teachers have long been taught that the side-on technique is the correct one. particularly of young bowlers whose epiphyses are not yet closed. a clear indication of a mixed bowling technique (Elliott et al. relatively high ball release positions.3 THE UPPER EXTREMITY The injuries to the upper extremity that are associated with technique will be considered under appropriate sport classifications. 1996.. from a more front-on position at backfoot strike in the delivery stride. 1989). 1992). the crash tackle is implicated in shoulder injuries to both the tackling . as the less coached West Indians might be held to demonstrate. 93 This last group included spondylolysis. usually after bilateral spondylolysis) or pedicle sclerosis (an increase in bone density of the pedicle or neural arch). A study of the 20 members of the western Australian fast bowling development squad (mean age 17. bony abnormalities. such as falling on to an outstretched arm. This supported earlier research at the University of Western Australia (for example. Such techniques should be avoided. Foster et al. 1995).
front view (horizontally spaced). bottom. . ball release. frontfoot strike. side view.10 Mixed technique fast bowler: top.94 Effects of sports equipment and technique Figure 3. From left: backfoot strike. mid-delivery.
can lead to sprains of the medial collateral elbow ligament. 1982). Impact and follow through may traumatise the fully stretched scapular origins of the posterior deltoid. This can result from a poor technique starting with an incorrect position of the wrist after withdrawal. The insertion tendons of pectoralis major and the anterior deltoid can be strained by forced stretch in the preparation for the badminton clear and tennis serve. 1992). Throwing Most throwing injuries are caused by overuse (Atwater. and ‘dropping’ the shoulder on the non-throwing side. are associated with several shot-put technique faults. Hyperextension of the elbow can damage the olecranon process. paralysis of the ulnar nerve or fractures of the olecranon. rhomboideus major and the long head of triceps brachii. particularly towards the end of the preparation phase. 1992). A faulty grip on the binding can injure the extensor pollicis longus (Reilly. Various tears of the tendon of the long head of the biceps brachii. Posterior shoulder injuries are most likely during the follow through. may lead to injury. Elbow injury is possible. Racket sports Injuries in tennis commonly occur to inexperienced players owing to flawed technique arising from too little emphasis being placed on the lower body (Nirschl and Sobel. the putting elbow too low or ahead of the shot. where a roundarm throw. In overarm throwing.Musculoskeletal injury—technique aspects and tackled player. and the wrist and finger flexors and extensors originating from the humeral epicondyles. Timing errors in the discus and hammer throws can also result in similar injuries to those in the shot-put. This is well established for the javelin throw (Kuland. at the limit of lateral rotation of the upper arm. 1994). it appears that to achieve the goal of the movement (maximum ball or implement speed) the desire to avoid injury is relegated to second place. particularly when the backs lie flat in defence to tackle hard and high to dislodge the ball. The stretch placed on the anterior soft tissues of the shoulder. and a wrong line of pull followed by pronation during the final elbow extension in an attempt to reduce javelin flutter. These include: poor coordination of arm and trunk muscles. incorrect alignment of the javelin before the start of the throw can rupture the pronator teres. Incorrect positioning of the thumb can injure the extensor pollicis longus (Reilly. where the maximum valgus stress on the elbow occurs. Atwater (1979) proposed that sidearm as opposed to overarm throws incur an increased injury risk. Sprain owing to 95 . rather than throwing with the classic elbow lead position. Incorrect timing of the shot-put can lead to injury to any of the rotator cuff muscles. 1979). with a spiral fracture of the humerus a rare injury caused by high inertia and large accelerations.
use of the whole body in the stroke. Kuland (1982) implicated a faulty backhand stroke using an Eastern forehand grip or a ‘thumb behind the handle’ grip and a high. particularly supraspinatus. Constant repetitions of shoulder movements can cause bicipital tenosynovitis. Impingement injuries of supraspinatus and biceps brachii tendons can be caused by technique or lack of strength and flexibility (Fowler. poor technique is a significant contributor. 1984). instead of just for impact. 1990). Tucker. Chan and Hsu (1994) considered good approach foot work. 1994. 1990). for club players and below. These actions cause friction between the extensor carpi radialis brevis and the lateral epicondyle of the humerus and head of the radius. An important factor is often not enough body roll to achieve a high elbow position during the front crawl recovery phase. ulnar deviation of the wrist and pronation of the forearm. also known as impingement syndrome.96 Effects of sports equipment and technique incorrect foot placement (40%) and strain from excessive movement (38%) have been most clearly associated with traumatic badminton injuries. hurried backswing. repeated stress on the extensor origin produces microtears. During the front crawl and back strokes. with use of shoulder muscle activity to compensate for this technique defect (Fowler. In addition. . Swimming The movements of complete arm circumduction in front crawl and back strokes can lead to ‘swimmer’s shoulder’. The results are adhesions between the annular ligament and the joint capsule. and including tendinitis of the rotator cuff muscles. 1994). 1994). 1994). which can lead to this overuse injury. He also considered poor use of weight transfer and shoulder muscles to be important. Tucker (1990) supported the feelings of many coaches and players that tennis elbow is most common in those players who put a great deal of top spin on the backhand. with too much of the power for the stroke coming from elbow extension. Many factors are associated with tennis elbow (see Curwin and Stanish. particularly in real and lawn tennis (Tucker. Injury can result from not training the correct stroke movements. the rotator cuff muscles contract strongly to contain and stabilise the glenohumeral joint (Fowler. Similar wrist extensor injuries can occur in other racket sports and from overuse of the backhand. and who tend to keep a tight grip for too long. and use of the two-handed backhand to be elements of technique that guard against tennis elbow. This is worse for inexperienced players who have more mistiming errors and off-centre hits. In tennis the spin serve can cause injuries around the medial humeral epicondyle. for example the medial and lateral rotation of the upper arm and pronation and supination of the forearm (J∅rgensen and H∅lmich.
In hockey. complete rupture of this ligament can occur leading to haemarthrosis of the knee. The poor technique often used by learners. the economically unsound running posture with spinal flexion is a contributory factor. of which about 85% is absorbed after impact by the hamstrings. This technique. repetitive jumping can cause patellar tendinitis and repeated forced dorsiflexion can lead to bony outgrowths in the calf or shin. as after an airborne knock. particularly with many repetitions. the leg contains about 900 J of energy.4 THE LOWER EXTREMITY 97 Team sports Injuries caused by the trunk twisting or turning while excessive friction fixes the foot were considered in section 3. known as unweighting. The ligaments and cartilage of the knee and ankle are particularly vulnerable. Where possible. along with straight-leg landing and single-step stops. Poor landing technique in the long and triple jumps can lead to groin.. can strain the medial hamstrings (Kuland. soccer and rugby. Tackling with a fully extended knee can tear collateral ligaments. Before impact in kicking.Musculoskeletal injury—technique aspects 3. can lead to tears of the medial cartilage and anterior cruciate ligament. reduces the normal component of ground contact force. 1982).2. this technique. Landing on a leg twisted under the player. for example in hammer-and discus-throwing. 1994). strain is a common injury. while the tibia rotates inwards stressing the anterior cruciate ligament. In soccer. twists and turns should be executed while the body is accelerating downward. for example. The sidestep swerve stresses the ligaments on the medial aspect of the planted knee such that the twist of the planted leg and contraction of the quadriceps femoris at push-off may laterally dislocate the patella. In tackling techniques in. soft tissues can be injured owing to the high impact loads. overstretching for the ball or poor kicking technique can strain the hamstrings or the quadriceps femoris. The crossover swerve stresses the lateral ligaments of the knee. The techniques involved in abrupt changes in speed or direction can dislocate the ankle joint or cause stress fractures of the tibia and fibula. A technique factor is also involved. If tackled at this time. Jumping Poor landing technique can cause chronic bruising of the soft tissue of the heel.4. accounts for most non-contact injuries to the anterior cruciate ligament (Henning et al. trying to kick with the medial aspect of the foot. as well as lower .
1994). For example. Swimming ‘Breaststroker’s knee’ involves a grade 1 medial (tibial) collateral ligament sprain caused by the knee extending from a flexed position while subject to valgus stress with the tibia laterally rotated in the whip-kick. damaging the deltoid ligament. when the swimmer fails to adduct the hips during recovery and then rapidly extends the knees with legs apart instead of keeping the heels together in the recovery and only moving the knees slightly apart in the thrust. with the thigh in forced abduction on landing. This should be avoided as it causes additional stresses on the medial aspect of the knee at ground contact. a good hurdle clearance technique without hitting the hurdles is preferable. Overconcern for airborne technique in the Fosbury flop can lead to a tendency to plant the take-off foot in an abducted and everted position. Large forces in the plantar flexors at takeoff in the pole vault can cause a total rupture of the Achilles tendon (McDermott and Reilly. this can also occur in the long and triple jump when reaching for the board. Uncontrolled landings between the phases of the triple jump can cause damage to the meniscus of the knee of the landing leg if the leg is torsionally loaded while the knee is flexed (McDermott and Reilly. because of the severity of the loading and the number of repetitions. An imbalanced landing on an inverted and inwardly rotated foot can damage the lateral collateral ligament and possibly cause a fracture of the lateral malleolus (McDermott and Reilly. In hurdling.98 Effects of sports equipment and technique back. 1992). can lead to adductor magnus or gracilis tears. Strain of adductor longus can arise from powerful adduction of the legs from a position of considerable abduction . particularly of two joint muscles. In sprinting. 1992). However. the whip-kick can predispose to injury even with a good technique (Fowler. an across-the-body arm swing accentuates pelvic rotation which can lead to inflammation of the muscle attachments on the iliac crest. injuries. If the trailing leg hits a hurdle it may cause the lead leg to land early with forced dorsiflexion of the ankle while the knee is fully extended. An imbalanced clearance technique. Running Running technique may be important in preventing injury. Because of the acute femoral shaft inclination. The technique of overstretching to maintain stride length at top speed is implicated in injuries. possibly tearing gastrocnemius. 1992). This can be caused by a faulty technique. fast and powerful but poorly coordinated contractions when fatigued can lead to muscle tears. some young female runners tend to recover the leg to the lateral side of an anteroposterior plane through the hip. for example of the hamstrings or hip flexors.
8). Any such full squat technique. 3. List and describe the important characteristics of a sports surface. 5. an understanding was provided of the effects of technique on the occurrence of musculoskeletal injury in a variety of sports and exercises. where the posterior aspects of the calf and thigh make contact. 99 In this chapter the important characteristics and behaviour of sports surfaces were considered. Attention was given to the injury moderating role of other sport and exercise equipment. Describe the methods used to assess sports surfaces biomechanically for vertical and horizontal load and energy loss. causes overstretching of the knee ligaments which may result in long-term damage. and the lower extremity. with special reference to impact absorption and rearfoot control. 1990). 6. 1990). 2. 3. Tucker.5 Summary 1. were also covered. 3. The lateral meniscus might also be trapped between the femoral condyle and tibial plateau.6 Exercises . 1994. Full squats with weights are therefore to be discouraged as a regular exercise. Tucker. 1990). Construct a table to compare and contrast these characteristics for a natural and a synthetic surface. After consulting at least one of the items for further reading (section 3. assess the injury moderating role of other sport and exercise protective equipment for the following parts of the body: head and trunk.Exercises with knees and ankles fully extended.g. The influence of footwear on injury in sport and exercise. Briefly outline the main features of sports surfaces related to injury. the upper extremity. Chronic overuse of the feet in the fully plantar flexed position can cause tendinitis of the extensor tendons on the dorsum of the foot in all the strokes (Fowler. Finally. The biomechanical requirements of a running shoe were considered including the structure of a runnmg shoe and the contribution of its various parts to achieving the biomechanical requirements of the shoe. Explain the contribution of the various parts of a running shoe to the biomechanical functions listed in exercise 5. with special reference to impact absorption and rearfoot control. The methods used to assess sports surfaces biomechanically and the injury aspects of sports surfaces were also covered. 7. with half squats being preferred (e. Describe the influence of footwear on injury in sport and exercise. List the biomechanical functions of a running shoe. Weight-lifting The strain on the knee as the lifter sits into and then rises from the deep squat or split position in the Olympic lifts is enormous (Tucker. 8. 4.
If you have access to a force platform. in Sports Injuries: Basic Principles of Prevention and Care (ed.C.. W. (1985) Biomechanics of running shoe performance. A. N. C. and Stanish.C. P. After consulting at least one of the items for further reading (section 3. Bartlett. England.Renström).H. R. (1984) The study of rearfoot movement in running. Frederick. London. Cuin. Blackwell Scientific.Frederick). Collamore. E & FN Spon. Brunet. USA.. M. USA.8).M. pp. Human Kinetics.Frederick). Stockill. 26–45. NJ. S. D. pp. Bartlett.F.C.W.F.7 References Atwater. D. Champaign. 43–85. Baker. Cavanagh.Miller). Blackwell Scientific. Lexington.W. S. (1993) Orthotics in injury prevention.F. IL. and Haddad. Champaign. E. England.A.D. 46–62. 10. Craton. IL.L.H. pp.E. Wolfe.. Blackwell Scientific. (1993) Protective equipment: biomechanical evaluation.P. England. in Sports Shoes and Playing Surfaces (ed.I. P.C. USA.J. R. (1980) The Running Shoe Book. P. CA. Curwin. P. Mountain View. T.C. (1989) Specific running injuries related to excessive loads.M. and Hsu. P. in Sports Injuries: Basic Principles of Prevention and Care (ed. 63– 116. Cook. Kester. and Hamill. 14.J. Elliott. Bell. Human Kinetics. E. describe the effects of technique on the occurrence of musculoskeletal injury in a variety of sports and exercises of your choice and relating to several parts of the body. in Exercise and Sport Sciences Reviews—Volume 7 (eds R. E. Chan. 417–428. 16–25.R. P. M.. Journal of Sports Sciences. 163–165. Journal of the Sports Turf Research Institute. (1996) The biomechanics of fast bowling in cricket—a review. (1986) Load on the locomotor system and modelling. S. including an analysis and discussion of the results.Renström). in Sports Shoes and Playing Surfaces (ed.M.Segesser and W. Clarke. (1984) Design and construction of a tuned track. (1984) Tendinitis: its Aetiology and Treatment. (1985) Playing quality of sports surfaces: a review.Pförringer).F.H. in Clinical Practice of Sports Injury: Prevention and Care (ed. A. B.Hutton and D. 355–373. Human Kinetics.D. England. pp. R. 3. and Canaway.. Becker.E. (1979) Biomechanics of overarm throwing movements and of throwing injuries. pp. London. Franklin Institute Press. London. (1997) Introduction to Sports Biomechanics.A. Bishop. USA. London. England. K. S. N. 61. in The Shoe in Sport (eds B. pp. (1994) Elbow injuries.M.. Clinics in Sports Medicine.C. pp. 619–626.S. 4. Design an experiment using humans to compare the effect on ground reaction forces of different surfaces or shoes. Anderson World. in Biomechanics of Running Shoes (ed.-L. 403–424. .Renström).Y. Your experimental design should include how you would seek to establish the validity and reliability of the results and how you would control for extraneous variables. IL. London.J. carry out this experiment.A. N. USA. New York. and McKenzie. USA. B. 166–189.Nigg).A. Champaign. and Burnett. M. J. pp.100 Effects of sports equipment and technique 9. Denoth.E.
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A. 76–86. McDermott. (1993) Excessive loads and sports-injury mechanisms. G. Nigg. (ed.J. D. Human Kinetics. A.Kvist).M. K. (1993) Prophylactic athletic taping. in Biomechanics of Running Shoes. (1994) Injuries in badminton. London. P. E.) (1986b) Some comments for runners. B. Barnes. 135–156.M. Kuland. England. P. M. 475–485. B. . pp. London. USA. implications and modification by footwear. England. USA. Blackwell Scientific.M. Misevich. in Nordic Congress on Sports Traumatology (ed. 98–118. Human Kinetics. (ed. K. pp. H. Frederick). 27–61. Champaign.H. (1982) The Injured Athlete.A. G. (1984) Functional standards for playing surfaces. Champaign.W. pp. London. pp. in Sports Shoes and Playing Surfaces (ed.P. P. pp. (ed. E. Lutz. G. (ed. B. (1992) Common injuries in track and field athletics— 1. T. London. 117–145. England. Nigg.) (1986c) Experimental techniques used in running shoe research.C. Moore.102 Effects of sports equipment and technique J∅rgensen. Turku. Nigg. pp.H. Champaign.B. T. Finland. (1987) Biomechanical aspects of playing surfaces.N.M. Human Kinetics. 47–75. T. and Renström.. PA.E.Frederick).Frederick). Pate. Racing and jumping. IL. COOB. 49. Mallon. IL. and Yeadon. pp. in Biomechanics of Running Shoes. and Cole. England. (1984) Material aspects of modelling shoe/foot interaction.M.C. 495–506. C. R. Champaign.Renström). (1986) Biomechanical approach to study man-shoesurface interaction. IL. in Biomechanics of Running Shoes.V. Human Kinetics.H. P. England. pp. Human Kinetics.F.L. Wolfe. IL. B. Komi.F. Lippincott. U. Nigg. B. measurement. in Second IOC World Congress on Sport Sciences.M. IL. 135–144. Archives of International Medicine. 1–26. Human Kinetics. Macera. Blackwell Scientific. P. Blackwell Scientific. pp. pp.A.F. E. 125–143. and H∅lmich. in Clinical Practice of Sports Injury: Prevention and Care (ed.M. 2565–2568. Champaign.A. Champaign. England.Reilly). P. Spain. P.R. M. USA. Philadelphia.H. in Sports Shoes and Playing Surfaces (ed. and Frank. et al (1989) Predicting lower extremity injuries among habitual runners. 388–397.) (1986d) Biomechanics of Running Shoes.H. P. 107–119.A. IL. and Reilly. USA. pp.F. Blackwell Scientific. Blackwell Scientific. pp. in Sports Injuries: Basic Principles of Prevention and Care (ed. Nigg.Renström). pp.Renström)..A.A. and Hawkins.E. P.E. Nigg.C. (1994) Injuries in golf. 118–119..R. Champaign. Wickiewicz. IL.W. Kolitzus.J.. London. USA. (1991) The effect of midsole hardness on internal forces in the human foot during running. and Gollhofer. B. in Sports Shoes and Playing Surfaces (ed. 5. Nigg. USA. Powell. in Sports Fitness and Sports Injuries (ed. B. and Cavanagh.F. Kupittaan Pikapaino Ltd.) (1986a) Biomechanical aspects of running. pp. USA.Renström). C. London.R. (1994) Traumatic knee injuries. in Clinical Practice of Sports Injury: Prevention and Care (ed. (1984) Skeletal heel strike transients. McLellan. in Sports Injuries: Basic Principles of Prevention and Care (ed. K. Journal of Sports Sciences.F. in Clinical Practice of Sports Injury: Prevention and Care (ed. 161–165. Barcelona.H. M. Human Kinetics. USA. R. R.Renström). W.J.
and Bojanic. and Nigg.Pförringer).. and Beynnon. and Luethi. J. Nirschl. Tipp.F. Parry.P. USA. pp.H. London.H. pp.Renström).F. and Tiegermann. Human Kinetics.A. in Sports Fitness and Sports Injuries (ed. 232–274. London. W. R.A.L. and Baumann.Terjung). and Watson. in Biomechanics of Running Shoes (ed. New York. Stacoff. Human Kinetics. England. O’Neill. London. in Sports Fitness and Sports Injury (ed.Nigg). (1996) Tennis rackets. Kreighbaum and M. USA.M. USA. M. B. (1982) Polymeric Surfaces for Sport and Recreation.. 139–161. London. in Sports Fitness and Sports Injuries. (1989) Rapid sideward movements in tennis. Bahlsen.Renström). A. Blackwell Scientific.Renström). Denoth. Wolfe.M.F. Franklin Institute Press. London. H. Reilly. pp.Renström). in Sports Injuries: Basic Principles of Prevention and Care (ed. Champaign. IL. Baudzus. The Sports Council. B. T.Reilly)..J.. B. (1993) Biomechanical response of body tissue to impact and overuse. 4. (1993) Sport shoe construction: orthopaedic and biomechanical concepts. A. A. and Sobel. IL. Sanderson. P.H. 398–416. England. I. (1989) Mechanisms of shock attenuation via the lower extremity during running. Wolfe. London. Applied Science. Norman. England. in Sports Shoes and Playing Surfaces (ed. England. (1992) Injuries in racket sports. Pratt. London. in Sports Injuries: Basic Principles of Prevention and Care (ed. Blackwell Scientific. pp. number 10 (ed. (1994) Injuries in tennis.F. P. F.Smith). R. IL.A. in Biomechanics of Running Shoes (ed. J. Pope.L. (1985) Running shoe degradation as related to the change in physical characteristics of the midsole material. Pinkowski.W. Polich. Champaign.Frederick). J. E. Human Kinetics. 460–474. pp.E. Clinical Biomechanics.Segesser and W.Lees). (1983) Biomechanical evaluations of sports protective equipment. (1986) Factors influencing kinetic and kinematic variables in running. (1986) Special aspects of shoe construction and foot anatomy. .H. (1984) On friction characteristics of playing surfaces. pp. pp. T. Wolfe. London.J. FL. Stacoff. British Association of Sports Sciences. T. Stucke.M. C. G. Stüssi. P. London. A. W. (1993) Overuse Injuries of the Musculoskeletal System. B. T. 87–97. 145–151. in Sports and fitness Equipment Design (eds E. B. USA. in Clinical Practice of Sports Injury: Prevention and Care (ed. Champaign. and Pförringer. Alsager. Boca Raton. England. London. pp. M.C.F. England. L. S. 85–95. in The Shoe in Sport (eds B. CRC Press. and Paulos. Human Kinetics. pp. 117–137. The throws. Blackwell Scientific.D. England. Wolfe. pp. in Proceedings of the Sports Biomechanics Study Group. (1990) The Shoe in Sport. Segesser. IL. Sports Council (1978 and 1984) Specification for Artificial Sports Surfaces—parts 1–3. Wolfe. England. R. P. et al. (1992) Soccer injuries. pp.H. 120–134. D.Reilly).A. K.M. in Sports Injuries: Basic Principles of Prevention and Care (ed. England. London.References 103 Nigg. Blackwell Scientific. (1993) Prophylactic knee and ankle orthoses. W. pp. England. in Exercise and Sport Sciences Reviews—Volume 11 (ed. B.M. V.H. (ed.A. pp. Segesser.H. 53–62.) (1992) Track and field—2. V. A. 127–132. Champaign. 175–182. B. Nigg). England.M. 374–387. England. Pecina. 51–57. USA.
(1993) Biomechanics of distance running. P. Renström. in Clinical Practice of Sports Injury: Prevention and Care (ed. IL. P. USA. (1994) Head injuries. C. (ed. pp. M. Williams. W. Oxford. England. Wolfe. (1990) The Mechanics of Sports Injuries: an Osteopathic Approach.M. including shoes for other sporting activities and the ski boot. and Yeadon.Grabiner). pp. London. Franklin Institute Press. Blackwell Scientific. this book has the advantage of covering a wide range of other sports footwear.A.W. 3–31. W. pp.H.) (1993) Sports Injuries: Basic Principles of Prevention and Care. in Sports Fitness and Sports Injuries (ed. Norman. USA. and Pförringer.A.A. J. pp. (1987) Biomechanical aspects of playing surfaces.F.S.R. van Mechelen. B.8 Further reading Nigg.Renström). P. Journal of Sports Sciences.Terjung). Human Kinetics. Although now somewhat dated. This provides a good review of the biomechanics of sports surfaces.H. (1992) Dangers and demands of basketball. London. this is an excellent review of sports protective equipment. Segesser.) (1994) Clinical Practice of Sports Injury: Prevention and Care. England.F. (1994) Cervical spine hip injuries. 105–111. P. London. England. in many cases including aspects of technique. Although several books and reviews deal with the running shoe. England. in Current Issues in Biomechanics (ed. T.Renström). 3–12. R. Blackwell Scientific. M. England.104 Effects of sports equipment and technique Torg. consider a variety of material specific to each sport. pp. R. London. (1990) The Shoe in Sport.H.F. England. Blackwell. 3. Renström.G. Champaign. (ed.H. Wilkinson.D. 13–26. 5. Blackwell Scientific. Blackwell Scientific. London. England. Tucker. (1983) Biomechanical evaluations of sports protective equipment. London.F. Wolfe.R. B. 117–145.A.Reilly). 232–274. New York. in Exercise and Sport Sciences Reviews—Volume 11 (ed. Chapters 28 to 32 contain useful summaries of many of the equipment aspects of injury. in Clinical Practice of Sports Injury: Prevention and Care (ed. on specific sports.L. K. W. . Chapters 18 to 25 and 27 to 47.H.
Degradation is owing to wear caused by mechanical pounding under the influence of degradative agents such as oxygen. Tartan) and find some use in other outdoor applications (such as tennis). It is caused by inadequate bonding between the rubber and asphalt. curing to a homogeneous rubber layer. It leads to a breaking of molecular chains and. they have a long life with correct maintenance. Both are of low compliance (concrete is worse). Here the crumb surface is beneficial by allowing the water to collect in the voids. typically. Having an impervious character. they are rigid. although asphalt is affected by temperature. about 200 mm thick. For such applications they offer the best combination of durability. They consist of a rigid wooden surface mounted on wooden joists. R=59%.Appendix 3. they behave elastically by exhibiting area elasticity. performance and ease of installation. and is exacerbated by penetration of the top layer by spikes leading to ingress of water and . Polyurethane rubbers have a coefficient of friction as high as 2 to 3. They weather well in general. This decreases the impact shock. they degrade with time. For a large weight. are layers of hot-rolled asphalt (about 25 mm) and dense bitumen macadam (about 10 mm).g. ultraviolet (UV) radiation and pollutants. Below this. the base must incorporate a slope. Both cross-linked polymeric polyurethane rubbers and natural or synthetic latex can be used. These surfaces are expensive (Tipp and Watson. A surface dressing of 1–3 mm of rubber granules is applied before curing is complete to give a balance between traction and underfoot firmness. moisture. They have both good traction (and are therefore fast surfaces) and high resilience. 1982). such as a dropped ball. but this is significantly affected by various factors including moisture. They are mixed on site and dispersed as free flowing liquids. a decrease in the elastic modulus plus an increased brittleness and hardness. for example.1 Artificial surfaces 105 CONCRETE AND ASPHALT The latter is often chosen as a sports surface by runners and used. Mechanisms of degradation lead to various types of damage. For small weights. thereby. which makes for considerable injury risk. Appendix 3. CAST IN SITU ELASTOMERS These are now the preferred surface for athletics (e.1 Artificial surfaces SPRUNG WOODEN FLOORS Popular for gymnasiums. although this can be retarded by various additives. for marathon running. exhibiting point elasticity. Delamination is affected by mechanical pounding and is most common in the inside lanes. In common with all polymeric surfaces. then a crushed and compacted base.
ball behaviour (Tipp and Watson. The base is important in providing the substrate for evenness and for withstanding loads in use. which provides dimensional stability. Major degradation is caused by compaction and loss of pile from wear loads and abrasion which can affect. They can be formed in situ or factory prefabricated as a sheet. . BOUND-CRUMB POLYMERIC SURFACES These are the most commonly used surfaces for outdoor games. tiles or slabs. 1982). They can also be loose laid. PREFABRICATED SHEETS OF ELASTOMER These find their main use in sports halls where a compromise between many sport and exercise activities is required. A crumb size of 1–5 mm is normal. They are joined in situ by rod-welding and trimming (PVC) or bonding and cutting (rubbers). Mechanical or chemical loss of surface texture leads to a loss of slip resistance when wet. They are usually adhesive-bonded to the sub-floor. The degree of compaction must be uniform as it affects mechanical properties such as tensile strength. SYNTHETIC FIBRE TEXTILE SURFACES Again mainly used in sports halls. for example. UV and thermal degradation may result in hardness and resilience changes. Particles of rubber (crumb or shred) are bound with a liquid polymer to give an elastomeric mat. A surface dressing is added to improve wear and slip resistance. these consist of a non-woven carpet of fibres bonded to a polyester substrate.106 Effects of sports equipment and technique dirt. Sheets are made of PVC or chloroprene rubbers and are a complex mixture of ingredients to produce the required behaviour. a backing of foam rubber or expanded PVC may be used. As they are used indoors. and are bonded to the underlying surface. A porous base (asphaltic concrete or bitumen macadam) is usual. and fixed to the base by adhesive or mechanical means. Large temperature changes may lead to dimensional instability (Tipp and Watson. although the long-term deterioration through wear is more important. and sections are joined by overlapping and cutting. To provide a high compliance. a binder is added to provide consistency for laying and this also affects the mechanical properties. degradation effects are far less than for the previous type although loss of adhesion can be caused by water. 1982).
and helps provide the correct playing characteristics (Tipp and Watson. Water affects resilience if the shockpad absorbs water and the cell structure breaks down. in which case the base needs to incorporate a 1 % slope to the sides and ends. The shockpad provides resilience. although slipping may occur. The anisotropy of woven and knitted carpets can influence ball behaviour. particularly for smaller balls. synthetic turf pitches are not allowed in English Premier League soccer. American football and baseball. structural integrity. This affects tensile strength and elongation (increased brittleness). reduces injury from falls. Stud damage is negligible compared with spike damage. impervious turfs are normally used. and hence traction. They are laid on a base of asphalt or concrete. lacrosse. hockey. 1982). 1982). 1982). injury reduction and ball bounce. Abrasion of fibres is due to repetitive bending. over several layers of stone and consolidated soil. Trapping of water between pile fibres is beneficial as it gives a more uniform ball roll. affecting ball behaviour. The resilience changes more than for cast in situ elastomers but this is less critical (Tipp and Watson. but degradation is reduced. crushing and splitting actions. for tufted products.1 Artificial surfaces 107 Being porous. no complete agreement exists on the size and shape of pile for optimum playing characteristics nor on sand or water filling and other important aspects of synthetic turf. The pile strands are secured to the backing by a rubber latex binder to provide flexibility and dimensional stability and. it uses synthetic fibres or ribbons woven or knitted into backing fabric (strands interweave) or tufted into previously made backing fabric. Because of pollution. Although used for tennis. although atmospheric pollution can cause silting. as it depends on installation. energy absorption and recovery. soccer. The compliance of the track is less predictable than for cast in situ elastomers. lower surface temperature and a reduction of friction burns. in contrast. of which compaction by crushing is the worst (Tipp and Watson. Water-based synthetic turf pitches have become increasingly popular for field hockey. SYNTHETIC TURF The newest of the sports surfaces. with an intervening shockpad of flexible foam. . Water retained in the pile can adversely affect balls and racket strings. as the coefficient of friction is direction dependent. as in lacrosse and hockey. a slightly lower bounce. such surfaces are genuinely ‘all-weather’.Appendix 3. impact. Degradation is caused by UV radiation because of a large exposed area. Temperature affects compliance.
2900 kN·m-1 for cinders. temperature changes. Surfaces should tolerate rain. Appendix 3. Surface safety relates mainly to flammability and most synthetics are flammable unless specially treated. ball behaviour. a compliance of two to three times that of humans was proposed as an optimum and incorporated into the experimental ‘tuned tracks’ at Harvard and. 1984) included a low. This is not always possible for synthetics owing to the clogging or silting effects of pollutants.55. it is more affected by moisture than pile height. uniform (±15%) vertical stiffness independent of contact area. It is. and a high horizontal stiffness to improve tread stability. The specification of these tracks (Cuin. . For carpet-type surfaces. a low surface mass to reduce impact stress. Porosity is an important property for outdoor surfaces to help removal of surface water.108 Effects of sports equipment and technique THE TUNED TRACK Greene and McMahon (1984) reported a reflex stiffness for runners in the range 73–117kN·m-1 with a damping ratio of 0. tearing and spike damage (wear resistance) all of which can lead to change in surface behaviour. however. level substructure. important in ball sports and should be consistent over the surface. and UV radiation (weathering). Typical values are 4400 kN·m-1 for concrete. The surface should be free from joints and irregularities (continuity) which might affect. later. Some materials deform (creep) under a continuous static load. high resilience. and 880 kN·m-1 for wooden boards. Because of the injury risks of stiff surfaces. They studied the effect of track compliance on running performance and found that the running speed is not significantly affected by the track stiffness until the latter falls below the runner’s own stiffness. Sport and exercise surfaces should resist abrasion.6 m plates of plywood coated with polyurethane rubber.2 Other surface characteristics Frictional resistance occurs not only for sliding but also when one object tends to rotate or roll along another. This should be withstood by the surface (set or creep resistance) so that permanent deformation (set) is not acquired. for example. Reports of the track’s performance claimed less injury. This was achieved by a subdivided deck of rigid 1. This was mounted on a resilient. Unfortunately the track was far too costly to have found a ready market. improved personal bests and longer training periods from a higher fatigue threshold.2 m by 0. which will otherwise affect rolling resistance. this ‘rolling resistance’ is considerably less than the resistance to sliding. Yale Universities. compressible series of synthetic rubber support units mounted on a firm.
Calculating the loads 4 This chapter is intended to provide an understanding of how the forces in the musculoskeletal system can be estimated. single muscle. and evaluate the various cost functions used • appreciate the uses and limitations of electromyography (EMG) in estimating muscle force • outline an example of muscle force calculations during a sports injury and the difficulties and limitations that exist even when this information is available. where necessary. This is usually supplemented. and for a segment chain. 4. by measurements of the external forces acting on the performer. The method of inverse dynamics is a crucial first step towards estimating the forces in muscles and ligaments and establishing injury . in planar motions • understand how multiple-segment systems can be analysed to calculate joint reaction forces and moments • appreciate the difficulties of calculating the forces in muscles and ligaments arising from the indeterminacy (or redundancy) problem (too few equations to solve for the number of unknowns) • describe and compare the various approaches to solving the indeterminacy problem • understand the method of inverse optimisation.1 Introduction The calculation of the forces and moments at the joints of the sports performer from segmental anthropometric and kinematic data is known as the method of inverse dynamics. After reading this chapter you should be able to: • calculate the joint contact and muscle forces for single segment. from a force platform for example. planar motions • understand and evaluate simplifications made in ‘inverse dynamics modelling’ • explain the terms in the equations for calculating joint reaction forces and moments for single segments.
as yet unknown. In this example these are: the weight of the forearm and hand (Fg=m g). We will begin by considering single body segments: first a static.1 STATIC JOINT AND MUSCLE FORCES FOR A SINGLE SEGMENT WITH ONE MUSCLE The example to be considered here is that of a single muscle holding a combined segment. case. 1995). produces the scalar equations of 4.1b) shows the biomechanical system of interest. The.1. A free-body diagram (Figure 4. an insight into the musculoskeletal dynamics that generate the observed characteristics of sports movements is also vital for a full understanding of those movements.1 can be calculated from kinematic measurements if the segment mass (m). the simplifications and assumptions involved will be highlighted. then the same segment but with several muscles. The effects of those surroundings are represented on the free body diagram as force vectors. the muscle force (Fm) and the x. and then look. the position (r) of its mass centre. at their centre of mass. as positive in the x. consisting of the forearm and hand. isolated from the surrounding world. joint force components are shown.110 Calculating the loads mechanisms.Fjy). The muscle force and joint force components in equations 4. which contains multiple-segment chains. Σ M=0). and angle of pull ( ) are known. here the forearm-hand segment.1) The first two equations come from the equation of force equilibrium. then Fjy will be downwards (negative). single muscle example. As Fm has an x-component to the left (negative as <90°) then Fjx is positive (to the right).2 Forces acting on a body segment in two dimensions 4. At all stages.and y-component directions. The forces will form a vector polygon (as in Figure 4. Applying the vector equations of static force (F) and moment (M) Σ equilibrium (ΣF=0. Some of these . We will progress to a two-segment kinetic chain.1a).1c). the examples considered in this chapter will be two-dimensional.2.and y-components of the joint force (Fjx. in principle. For the sports biomechanist. as Fm will be shown in the example below to have a y-component upwards (positive) that is larger than the weight downwards (negative). at how we can extend the procedure to the whole human musculoskeletal system. by convention. and then a dynamic. Because of the complexity of calculating forces and moments in three dimensions. the muscle moment arm (rm). or spatial. Fjx-Fm cos =0: or Fjx=Fm cos Fjy+Fm sin -m g=0: or Fjy=-Fm sin +m g rm Fm sin -r m g=0: or Fm=r m g/(rm sin ) (4. see Andrews. 4. or planar (for a consideration of the more general three-dimensional. in a steady horizontal position (Figure 4.
Bartlett. values can be estimated experimentally and the rest obtained from standard anthropometric data (see. . (b) free body diagram.1 Static forces on single segment with one muscle: (a) forearm and hand. for example.Forces acting in two dimensions 111 Figure 4. 1997). (c) vector polygon.
or angle of pull.81) N =-35.) The vector polygon for these forces is shown in Figure 4.81 m·s-2/(0. then Fjy acts downwards. but with the direction of its angular velocity . that is. the forearm and hand are assumed to move together. The polygon is a graphical expression of the vector equation: 0=ΣF=Fm+Fj+Fg=Fm+Fjx+Fjy+Fg.112 Calculating the loads Example The mass of the forearm-hand segment of an athlete is 2 kg and the centre of mass of the combined segment is 14 cm (0. Here. (ii) verify the answer using a force polygon. in an instantaneously horizontal position as it rotates with an angular acceleration (a) and angular velocity ( ). not upwards as was assumed.1b: (i) calculate the muscle force and the components of the joint force.75/(0.2a) again shows the forearm–hand segment isolated from the surrounding world. If the forearm-hand segment is stationary and horizontal as in Figure 4. right hand equations: Fm=rm g/(rm sin ) Therefore: Fm=0. This polygon is closed as the forces are in equilibrium.8×0. The free body diagram (Figure 4. Flexion is assumed to be performed by a single muscle that inserts 5 cm (0.8 N×0.8 N×sin80°+2 kg×9.05×0.14 m) from the elbow joint.8 N (note that this is much larger than m g) Fjx=Fm cos Therefore: Fjx=55.1736 =9. Σ 4. ( ) of 80°.1c.2 DYNAMIC JOINT AND MUSCLE FORCES FOR A SINGLE SEGMENT WITH ONE MUSCLE The example to be considered here is that of a single muscle holding a combined segment. consisting of the forearm and hand.8 N×cos80°=55.14 m×2 kg×9.69 N Fjy =-Fm sin +m g Therefore: Fjy=-55.2.05 m) from the joint with an angle of insertion.9848) N =55.05 m×sin80°) =2.1. from the Latin word quasi meaning ‘as if or almost’). From equation 4.9848+2×9. the two segments behave as a rigid body (this is sometimes called a quasirigid body.81 m·s-2 =(-55.2 N (Note: as this value is negative.
g is downwards (negative). To calculate the linear acceleration components. magnitude 2r. To convert these equations into scalar equations to calculate the three unknown forces. magnitude ar. The muscle force and joint force components are then obtained from the following equations: Figure 4. Fjx-Fm cos =m ax Fjy+Fm sin -m g=m ay rm×Fm+r×(m g)=Ioa (4. Bartlett. and a centripetal component. we must use the magnitudes and directions of all forces and moment arms. assumed to be at O. 1997) are: for force (F=ma). the convention that these are positive anticlockwise is used here.2) In the third of these equations. we note (see Bartlett. a. The two moment arms are positive (left to right) for this example. 1997) that this segment rotating about a fixed axis (O) with an angular acceleration. and for the moment (M =Io a). for example.Forces acting in two dimensions 113 and acceleration shown. the muscle moment is the vector (or cross) product of the muscle moment arm and the muscle force. has a tangential component of acceleration. and velocity. (b) tangential and centripetal acceleration components. In this case ax=– 2r and ay=ar. Fm has an xcomponent to the left (negative) and a y-component upwards (positive). whose directions are as shown in Figure 4. The vector equations of the linear and rotational second laws of motion (see.2 Dynamic forces on single segment with one muscle: (a) free body diagram.2. where a is the linear acceleration vector of the mass centre and Io is the moment of inertia about the joint axis of rotation. Applying these produces the vector component equations of 4.2b. . .
14 m) from the elbow joint.09 kg·m2. If the forearm-hand is instantaneously horizontal. Example As in the example in section 4. we now need to know the angular velocity and acceleration (or the mass centre acceleration components). The moment of inertia of the combined forearmhand segment about the elbow joint is 0.3: . calculate the muscle force and the components of the joint force.1.2.114 Calculating the loads Fjx–Fm cos =-m 2 r Fjy+Fm sin -m g=m a r rm Fm sin -r m g=Io a (4. as in Figure 4.2b. the mass of the forearm-hand segment of an athlete is 2 kg and the centre of mass of the combined segment is 14 cm (0.5 rad·s-2 and angular velocity of 2.05 m) from the joint with an angle of insertion ( ) of 80°.3) In addition to the values needed to calculate the three forces in the previous example. From equation 4. Flexion is assumed to be performed by a single muscle that inserts 5 cm (0.5 rad·s-1. with an anticlockwise (positive) angular acceleration of 1. and the segment’s moment of inertia about O.
This will not be true.Forces acting in two dimensions 115 4. extensor carpi ulnaris. as in many sports movements. palmaris longus and flexor digitorum superficialis) and pronator teres and supinator. owing to bony pulleys. The points of insertion and the angles of pull of the muscles are assumed to be known. for example. the soft tissue movements are not the same as those of the rigid bone. along with comments on their ‘validity’.7. The solution can be generalised to non-horizontal cases. These assumptions are stated below. a more complex ‘wobbling mass’ model may be needed (e. is that only the three main elbow flexors contribute to the muscle moment at the elbow joint.2. 1994). 1995). in such cases. made in the next section. through O. the wrist and finger flexors (flexores carpi radialis and ulnaris. The muscles are also assumed to pull in straight lines. • • • • . which can lead to large errors in moment arms (Pierrynowski. again. Nigg. when the elbow is itself rotating about the shoulder. More realistically. assumption that was made to simplify the problem. length. Also. whereas most do not. and generally false. Even then. • The motion is planar (two-dimensional) and the muscles exert their pull only in that (the sagittal) plane. centre of mass location and moment of inertia throughout the motion to be studied (forearm flexion). for example. wrist and finger extensors (extensores carpi radialis brevis and longus. Even this assumes no activity in the elbow extensors (triceps brachii and anconeus). at least. in impacts. as shown in the next section and in exercise 2 in section 4. anatomical data are generally only precise to about 2 cm. The validity of some.3 ASSUMPTIONS UNDERLYING THE ABOVE MODELS Some simplifying assumptions were made in arriving at the representation of the forearm-hand segment model. extensor digitorum and extensor digiti minimi). This is a large. This would clearly not be so if the wrist joint flexed or extended. An inertial (non-accelerating) frame of reference is located at the axis of rotation of the elbow joint. each muscle should be represented by a three-dimensional line or curve joining the centroids of its areas of origin and insertion. of these assumptions would require electromyographic (EMG) investigation. The assumption that the segment was horizontal was. The combined forearm-hand segment behaves as a rigid body and has a fixed and known mass.g. Only one muscle acted to cause the motion. made only to simplify the resulting equations. A more reasonable assumption.
2. The fifth force (Fp) is that due to the ligaments and capsule of the joint (and other soft tissues around the joint) and is caused by their passive elasticity. as assumed above.3a can be generalised to a dynamic one. Assuming that the passive force and moment are negligibly small and that the force in brachioradialis is small in comparison with those in the other two agonists would not remove the indeterminacy. The joint reaction force components. this has an associated moment (Mp). these two equations contain five independent unknowns.3c).116 Calculating the loads 4. 4. Applying the equations of static force and moment equilibrium (that is the sum of all the forces equals zero and the sum of all the moments equals zero) now gives: (4. The method involves reducing the number of unknown variables by replacing the actual muscles by a single muscle group. In this case. are . will be returned to later in the chapter. Fj. biceps brachii (Fbb). in the second equation. and the joint contact force. These are the forces in the three flexors. The difficulty of obtaining values of these forces.4) is said to be indeterminate as n equations can only be solved if the number of unknowns does not exceed n. we have two equations and five independent unknowns (Fp and Mp are interrelated). The system of Figure 4.3a.3b. If. Fx. Fy.4 FORCES ACTING ON A BODY SEGMENT WITH MORE THAN ONE MUSCLE—THE INDETERMINACY PROBLEM A schematic free body diagram of the static forces acting on the forearmhand segment when we introduce a more realistic representation of the muscles acting is shown in Figure 4.4) where. brachialis (Fb) and brachioradialis (Fbr). which are particularly important in understanding injury. Instead of trying to calculate the individual muscle forces and the actual force in the joint.2. the moment arms (r) of the three muscle forces are known. this exerts a joint reaction moment.5 PLANAR JOINT REACTION FORCES AND MOMENTS FOR A SINGLE SEGMENT One way of tackling the indeterminacy problem is to sidestep it. Mo (Figure 4. A pair of equations (such as 4. the angular velocity and acceleration and the component accelerations of the mass centre are shown in Figure 4. we calculate the so-called joint reaction forces and moments (sometimes called the net joint forces and moments). the muscle moments are the vector products (×) of the muscle moment arms and muscle forces. equivalent to that exerted by the individual muscles. if the passive elasticity (which is usually small) is neglected. as we would still have three unknowns and only two equations.
3 Forces on single segment with more than one muscle: (a) free body diagram.Forces acting in two dimensions 117 Figure 4. . (b) tangential and centripetal acceleration components. (c) joint reaction forces and moment.
In these equations. .5. however.5) where with ko and kg being. However. ax and ay are the x and y component accelerations of the mass centre (G) of the segment.5 gives: (4. provide information about the joint contact forces or the forces in the muscles. therefore. r.6) The joint reaction force components are both seen to provide centripetal (r 2 ) and tangential acceleration (r a) of the segment.2 sin +a cos ). the reaction forces also include contributions from the muscle and passive elastic forces. the joint reaction forces and moments do provide important information about the dynamics of the movement. Applying the equations of force and moment equilibrium produces equations 4. For a single segment motion.5 can be calculated from kinematic measurements of the segment angle ( ) and angular acceleration (a) and the position (r) and acceleration components of its mass centre if the required segmental anthropometric data (k. the radii of gyration of the segment about O and G respectively.5. and their extension to two or more segments and more complex segment chains. Then ax=-( 2 cos +α sin ) and ay= (.c). (4.118 Calculating the loads the components of the force exerted by the adjoining segment (the upper arm) on this segment. and whose mass centre is a distance. which has mass m. Some interesting features of the movement can. the contributions of the segment’s motion to ground reaction force to be assessed. The joint reaction moment provides the angular acceleration of the segment (a) and balances the gravitational moment. These reaction force components do not. correspond to the components of the joint contact force. however. with the y-component also supporting the segment’s weight (mg). from the axis of rotation (O). are the ones that should be used for inverse dynamics calculations.6 enable. m and r) are known. The resulting analysis does not. respectively. equations 4. The joint reaction forces and moments in equations 4. They involve fewest calculations and thus minimise the propagation of errors owing to measurement inaccuracies in the values of the kinematic and anthropometric variables. Equations 4. for example.3b. be revealed by resolving the accelerations in the x and y directions into ones along and tangential to the segment’s longitudinal axis (Figure 4. Substituting these into equations 4.
2. The exact meaning of the interactions between segmental angular velocities may seem somewhat obscure. As evidenced by. joint reaction forces and moments can be calculated by extending the Newtonian approach of the previous section. however. This analysis can be extended to consider movements with angular acceleration of the segments. The use of a more elegant (but also more complex) mathematical technique. 4. A full interpretation of equations 4. in such segment chains. A reduction in the vertical ground reaction force occurs if the segment is above the horizontal (that is 0< <180°. Such an insight is useful. Andrews. such as a single limb. For a chain of two segments (Figure 4.Forces acting in two dimensions 119 For the simplest case. g. Examples of this include take-off in the long jump and high jump. that the 2 terms are centripetal. be obvious that. such as the Lagrange Formalism (e.7) where the coefficients c1 are combinations of various segmental anthropometric (inertial and geometrical) quantities as follows (see Figure 4.6 PLANAR JOINT REACTION FORCES AND MOMENTS FOR SEGMENT CHAINS For non-compound segment chains.g.5. the .2. for example. in comparison with section 4. Fy=-m 2 sin +m g.5 and as is evident from the coefficients c1 and c2. Kane and Levinson. statements such as ‘flexors flex’ or ‘muscles generate angular accelerations at the joints they cross’ are oversimplified.5. as in section 4.4 for nomenclature): The symbols are the masses and moments of inertia about the centres of mass for segments 1 and 2 respectively.2. and can aid weighting and unweighting. so that sin? is positive). 1995) or Kane’s method (e. It should.7 is much more complex than for the example in the previous section. as appropriately timed motions of the free limbs are considered to make an important contribution to the ground contact forces acting on the sports performer.2. 1985). The a1 and a2 terms account for the moment required to angularly accelerate the respective segment. It should also be evident. so that sin is negative). is often preferred in advanced biomechanics research.g. The first terms on the right side of each equation represent the muscle moments required to raise the segment(s) against gravity. as in section 4. of constant angular velocity.4) the result for the joint reaction moments is as follows: (4. the segment’s rotation then causes an increase in the vertical ground reaction force (Fy) above the weight of the sports performer (m g) if the segment is below the horizontal (that is 0> >-180°.
square-bracketed terms in equations 4. Zajac and Gordon. not just the ones they span. 1989). and the .7.4 Two segment kinematic chain. Many interesting relationships have been reported between joint reaction moments and muscle action (see. in multi-joint movements. This is evident for the acceleration effect of the soleus on the ankle. the joint reaction moment at each joint in the segment chain depends on the kinematics (and some anthropometric properties) of all segments in the chain. all muscles tend to accelerate all joints. 1989). which it spans. and the acceleration effect at an unspanned joint can exceed that at a spanned joint (Zajac and Gordon. for example.120 Calculating the loads Figure 4. For example.
the soleus acts more to accelerate the knee into extension than it does to accelerate the ankle into plantar flexion (i. The roles normally ascribed to the gastrocnemius—ankle plantar flexion and knee flexion—only apply for moment-arm ratios greater than 0.5 and. depending on this ratio. The action of the muscle at the ankle depends on whether its plantar flexor torque at the joint exceeds the ankle dorsiflexor action produced by the muscle’s knee flexor torque.5a). which it does not (Figure 4.5b (Zajac and Gordon. A two-joint muscle that applies a direct moment to accelerate joint A into flexion and joint B into extension can actually accelerate joint B into flexion or joint A into extension.7). 1989) . In practice. For knee angles of greater than 90° (when the knee is flexed through less than 90° from its straight standing position).e. the ratio of knee to ankle acceleration is greater than 1).5b) for the effects of the gastrocnemius on the knee and ankle joints in standing (Zajac and Gordon. the muscle is rarely a major accelerator as it works near the boundaries of the regions in Figure 4. 1989). such apparently paradoxical phenomena may be common in such movements. This is shown in the three regions (Figure 4. Inertial coupling (the effects of the acceleration components of one segment on another) also plays an important role in this respect during movement (as in the square-bracketed terms in equations 4. Figure 4. knee angles between 90° and 135°. As inertia forces can be large in sports movements.5 (a) Ratio of effect of soleus muscle on knee and ankle angular acceleration. This shows how the roles played by the gastrocnemius at the knee and ankle joints are affected by both the knee angle and the ratio of the muscle’s moment arms at the two joints. 1989).Forces acting in two dimensions 121 knee. (b) effect of gastrocnemius muscle at knee and ankle (after Zajac and Gordon.
here (d) and (e). and the . 1994). is designated as the ‘primary chain’. until an articulation with the secondary chain (marked #). 1978). as ‘tertiary’ chains.6 (Aleshinsky and Zatsiorsky. 1978). and use the forces and moments as inputs to the primary chain at *. The degree of indeterminacy of the resulting equations generally increases with the complexity of the problem. as in Figure 4.2. from the segment furthest from ground contact towards the ground contact point.6a). which is treated similarly until its articulation with the primary chain. Andrews. Yeadon and Challis. Stop the calculations again. 1990) that can be obtained accurately from photographs of an athlete with few physical measurements (Yeadon and Challis. They treated both girdles as rigid triangles and subdivided the multiplechain system similarly to that above. while proceeding along the primary chain towards the ground contact point. it has a three-dimensionality which must be taken into account. For each of the tertiary chains. Stop the calculations at that point and use the calculated values at # as inputs to the secondary chain.7 JOINT REACTION FORCES AND MOMENTS IN MULTIPLESEGMENT SYSTEMS The segment chain approach of the previous section can be extended to complex multiple-segment systems. 1995). 1994). the difficulty arises of devising satisfactory representations of the pelvic and pectoral girdles.122 Calculating the loads 4. Zatsiorsky and Fortney. One of these chains. with the rest. The use of inverse dynamics to calculate joint reaction forces and moments raises many other important issues that have been addressed elsewhere. the need for individual-specific inertial parameters (Reid and Jensen.g. One attempt to devise a suitably simple model of the two girdles that attach the extremities to the axial skeleton is shown in Figure 4.6 (from Aleshinsky and Zatsiorsky.g. • Consider the multiple-chain system (a) to be made up of four single kinetic chains (b) to (e). at *. in this case (b). this will not be considered here. However. 1993). The two-dimensional examples used for simplicity above can be extended to three-dimensional motion (e. • • • For frontal plane movements.g. in this case (c). To calculate the forces and moments at the segmental articulations in such a representation of the sports performer. and what errors might arise from its use in calculating joint reaction forces and moments. calculate the reaction forces and moments at each joint. the ‘secondary’ chain. These relate to: data collection in the sports environment (e. The shoulder girdle is far more complex and should strictly be treated as a dynamically distinct region. It is left to the reader to consider whether such a representation is acceptable. data processing (e. another. one procedure is as follows (see Figure 4. Whereas the former is rigid.
. (below) frontal plane.123 Figure 4.6 Multiple-segment kinetic chains: (above) sagittal plane.
Gregor and Abelew. An et al. Other assumptions might be made. Oversimplified models of this type can. lead to errors.2.. its use in sport is likely to be limited.3. as are its limitations. 1986). the lack of accurate and non-invasive methods of estimating muscle and ligament forces is a crucial issue in biomechanics (Norman. The indeterminacy in equations 4. 1997). the reaction forces and moments at the joints of the sports performer can be calculated by inverse dynamics.3. it may be sufficient to combine the unknown forces and moments into an effective force on the segment (the joint reaction force) and joint reaction moment as in section 4. These must never be confused with the joint contact force and the moments (or torques) of individual muscles or muscle groups. for which some form of tendon transducer would be needed. 1990) is obvious. 4. This approach does not allow the direct calculation of the actual forces acting on joints and bones and within muscles and other soft tissues. The value of direct measurement of tendon force (e. However.. it allows calculation of the joint force but not the detailed contributions of individual muscles. The contribution of the participating muscles to the joint moment can be estimated by functionally grouping the muscles and making the system determinate (e. Various approaches have been used to tackle the indeterminacy problem to estimate the joint contact force and the forces in the muscles and other soft tissues.1 SOLVING THE INDETERMINACY (OR REDUNDANCY) PROBLEM As was shown in the previous section. 1995). a single force • • . The assumptions made need to be validated from EMG. it has great value for validating other methods of estimating muscle force.124 Calculating the loads systematic evaluation of measurement errors in biomechanical data and their effects on calculated variables (Challis. and ethical issues. This has been termed the reduction method (e. the few tendons for which it is suitable. such as the inverse optimisation approach discussed in section 4.3 Determination of muscle forces from inverse dynamics 4. Gregor. however. • To calculate the dynamics of the system (for use in technique analysis). Komi. It represents a major obstacle to the contribution that biomechanists can make to the prevention and rehabilitation of sports injury. for example that the passive force is negligible.g.4 could be overcome if the three muscle forces could be measured. This might be acceptable for vigorous sporting activities. The following approaches to the indeterminacy problem can be identified (see also Herzog. Because of calibration difficulties.g.2. As an example. 1989). 1996). 1993.g. 1994. However. Harrison et al.
and n is an index. This predicted compressive loads exceeding vertebral end-plate failure tolerances for lifting loads that could actually be performed with no illeffect.4. Although much research has been carried out to establish the relationship between EMG and muscle tension. This equation therefore serves as one constraint (known as an ‘equality’ constraint) on the force distribution.Muscle forces and inverse dynamics 125 vector representation of the back extensor muscles linking the spinous processes 5 cm from the centre of the discs was used by Chaffin (1969). If these passive (mostly ligamentous) forces and torques can be neglected.9) where U(t) is the cost function. • 4. 1994). usually a positive integer.4) has been neglected. normally among only the muscles (not the ligaments) of that joint (see Herzog. Such an algorithm minimises or maximises a suitable ‘cost’ or ‘objective’ function. The muscle force distribution arrived at must still satisfy the joint reaction moment (M) equation of inverse dynamics. usually of the form shown in equation 4. Further constraints may also be imposed on possible .8) where Fmi are the muscle forces. Such techniques include various forms of optimisation. ki are constants (for example. pcsai. 1996). The estimation of ligament forces is briefly covered in section 4. the joint reaction force equation of inverse dynamics can then be used to estimate the joint contact force.2 INVERSE OPTIMISATION The calculation of the joint reaction forces and moments from inverse dynamics serves as one of the inputs for inverse optimisation.9: U(t)= (Fmi /ki)n (4. Other approaches involve modelling the system in more detail to seek to identify the way in which the joint torque is partitioned between muscles (force distribution or load sharing). The use of an optimisation algorithm to represent a hypothetical control of movement by the central nervous system has an intuitive appeal. The question now arises of how the forces are apportioned between the relevant muscles.3. little agreement exists on that relationship for dynamic voluntary muscle contractions. This is expressed by: M= (Fmiri) (4. and attempts to infer muscle tension from the EMG signal (see also van den Bogert. the muscle physiological cross-sectional areas. rj are the muscle moment arms and the passive elastic torque or moment (Mp in equation 4. This is an attempt to apportion the joint reaction moment.
for which n=1 in equation 4. 1967) has the constants (ki) in the cost function (equation 4. 1978). only one muscle would be recruited. 1984). In equations 4. Siemienski (1992) used a ‘soft-saturation’ criterion. This cost function preferentially recruits the muscle with the largest moment arm. Yeo. the muscle forces are the variables (these are called the design variables) that are systematically changed until the cost function is optimised while the constraint functions are satisfied.8a. In this. The sum of muscle forces (e.8a.g. Without that constraint. Crowninshield. pcsa) (e. for example. Other non-linear functions include the muscle force normalised to either the maximum moment the muscle can produce (e. This approach has been extended. 1978. for elbow flexion. somewhat more natural results (Figure 4.7). 1987a. for example the brachioradialis for elbow flexion. Pedotti et al..9) equal to unity. Crowninshield and Brand.g. of muscle force and muscle stress (e. shows the three elbow flexors to be recruited in sequence. 1981a. Many cost functions have been proposed and tested (see. Siemienski. These include nonlinear functions. to the activity of the lower limb muscles in sprinting (Siemienski. 1992). 1978). Pedotti et al. Minimising muscle energy. This example.b) or the maximum force in the muscle (e. Herzog... the smallest of the hip abductors. . 1995).. such as maximal tissue ‘stress’. These are mathematically convenient but only predict synergy if the first recruited muscle reaches an enforced inequality constraint. Some of these have predicted results that do not conform to physiological reality (An et al. for example. but is contained within the cost function. This criterion produces.126 Calculating the loads muscle force distributions. such as: Fmi/pcsai max (4. for example. equation 4.9. favours muscles with lower contraction velocities because of shorter moment arms. 1978).g.10 (Figure 4. Other cost functions have been reported. the muscle stress limit does not have to be applied as a separate constraint. Pedotti et al. than Figure 4. for example the tensor fasciae lata.10.b). related to the velocity of contraction (Hardt. where U(t)= (Fmi/pcsai) and (Fmi /pcsai) max. 1992). many of which have been claimed to be related to some physiological property. King. These include linear functions. where n>1 (e. where U(t)= √(1-(Fmi /( maxi pcsai)).7). 1976 based on MacConaill.g.8 to 4.10) where max is the maximal muscle ‘stress’.8b). These are normally in the form of ‘inequality’ constraints.g. Figure 4. The muscle recruitment patterns predicted from such assumptions have generally been contradicted by EMG evidence (e. 1978) favours muscles with greater products of moment arm and pcsa (as in Figure 4.g. an additional muscle being recruited only when the previous one reaches the enforced inequality constraint. The sum of muscle ‘stress’ or ‘specific tension’ (force divided by physiological cross-sectional area.g.
Figure 4. Gracovetsky (1985) proposed that optimal locomotion dictates that the stresses at the intervertebral joints of the lumbar spine should be minimised. for . Crowninshield and Brand (1981a) used minimisation of the cube of muscle stress. Schultz and Anderson (1981) also minimised the compressive stresses in the lumbar spine. Reducing muscle fatigue by maximising the muscle endurance time (the maximum duration for which an initially relaxed muscle can maintain the required output (Dul et al. 1991) has also been considered as a cost function for inverse optimisation. 1992) Minimising neuromuscular activation (Kaufman et al.Muscle forces and inverse dynamics 127 Figure 4. which has since been disputed as a measure of endurance time. and that the central nervous system modulates the moments at these joints. with a maximum stress of 1 MPa.7 (a) and (b): Effects of two different sets of moment arm and pcsa values on muscle recruitment sequence.. Such minimum compression schemes do not account for antagonist contractions (McGill and Norman. (b) soft-saturation (after Siemienski..8 Non-linear cost functions for three agonist muscles (1–3): (a) sum of stresses squared. 1984a)) appears relevant for endurance sports. 1993).
b). sum of cubes of muscle stresses.g. linear criteria (after Dul et al. 1981a). if anything. such as muscle. the cost function may need to be implemented in stages—for example minimise the Figure 4. the physiological data to substantiate the choice of cost function are not. although it is unclear what. and the percentage of slow twitch fibres. the central nervous system does optimise. 1987b). They showed that the predicted (MF) force distribution for muscles with unequal proportions of slow twitch fibres was non-linear. and more realistic than. note that only MF gives a non-linear distribution. 4. 1984a). It is in clear contrast to. for example as speed changes (Herzog and Leonard. the linear load sharing predicted even by non-linear muscle stress and normalised muscle force cost functions (see Figure 4.128 Calculating the loads example by Denoth (1988). It could vary for different performers and during an event. although this has been questioned (e. Dul et al. 2. 1991) or at the onset of fatigue.9a. Q1. .9a. Alternatively.9 (a) Muscle force distribution during knee flexion for different nonlinear criteria: MF minimum fatigue. 3. Possibly the cost function needs to include weighted criteria. respectively. C sum of cubes of muscle stresses. (b) Range of more than 95% of experimental results (between dashed lines) and predicted load sharing for two cat muscles: 1. for example maximising speed in sprinting and minimising energy expenditure in long distance running. in general. 5. Furthermore. It would appear that a cost function based on maximising endurance time would have little relevance to explosive athletic activities such as throwing and jumping. (1984a) used a function of muscle force. This non-linearity is evident for gastrocnemius (48% slow twitch fibres) and the long or short hamstrings (67% slow twitch fibres) in Figure 4.9b). Dul et al.2 sums. yet available. quadratic sum of normalised muscle forces. by Herzog. The cost function used should relate to some relevant physiological process. of normalised and non-normalised muscle forces. minimum fatigue. The cost function is likely to depend on the specific sports movement. quadratic sum of muscle forces. its maximum value.. (1984a) reported good agreement between their force distribution predictions and tendon transducer experiments (Figure 4. ligament and joint forces (Crowninshield and Brand.
The cost function of Crowninshield and Brand (1981a): . n is even in equation 4.g.. such as moment arm and physiological crosssectional area (Figure 4.. 1978. Solutions to the force distribution problem have generally ignored any contribution of ligament and joint contact forces to the cost function and the net muscle moment. 1988). The solution to the force distribution problem is predetermined by the choice of cost function (e. The difficulty of solving inverse optimisations analytically relates directly to the number of design variables and constraints. 1981b) and it ignores any neuromotor role of ligament mechanoreceptors (Grabiner.g. It is sensitive to small changes in the anatomical data used. upper band of muscle stress then the sum of muscle forces using the optimal muscle stress (Bean et al. 1993).. 1991).7).g. The results from the cost function chosen should be evaluated. This may represent a significant simplification for joints such as the knee (Crowninshield and Brand. 1984b).8).. linear cost functions offer simple solutions. from Dul et al. particularly as small changes in assumptions can markedly influence the estimated forces (as in Figure 4. Herzog.10 Comparison of rectus femoris muscle force predictions using different cost functions (Crowninshield. Dul et al. 1981 a. as little evidence exists that the muscle forces are estimated accurately (e. 1987b).10).b) and maximal muscle stress (Crowninshield. Comparisons that have been made of force distributions using different cost functions (e. Because muscle forces are zero or positive (tensile).g.7a. An et al. 1984a) with a criterion value obtained for a dynamic knee extension exercise with a knee angle of 150° (after Herzog. as do cases where the cost function is ‘convex’ (e.Muscle forces and inverse dynamics 129 Figure 4. 1995). Dul. 1987b) have shown differences between them (Figure 4. from Crowninshield and Brand. Herzog and Leonard. The need remains to refine and develop experimental techniques to do this.
as in Figure 4. 1995). where the cost function is defined over the time course of the activity (Winters. inverse optimisation has failed.11 Schematic diagram of optimal force distribution between two muscles for a single degree of freedom joint (after Herzog and Binding.. Also.130 Calculating the loads U(t)= (Fmi/pcsai)3 (4. for example by Crowninshield (1978) in the brachialis and triceps brachii (medial head) in forced elbow extension. it does not account for co-contraction of antagonist pairs of single joint muscles. Prilutsky et al. For example. An inverse dynamics integrated optimisation approach.12 (Herzog and Binding. 1993). 1994) . the Figure 4.11) reduces to a convex one for a one joint planar movement with two muscles. They have not often been used for the fast movements that occur in sports activities (but see McLaughlin and Miller. these have been called. 1980). respectively. Such co-contractions have been measured using EMG. may prove more appropriate for such movements. to predict the loops in muscle force curves that are frequently reported from force transducer studies (e. 1995). The reader interested in a mathematical consideration of the general inverse optimisation problem is referred to Herzog and Binding (1994). In this case: Fm1=Fm2 (r1/r2) (pcsa1/pcsa2)3/2 (4.12) The solution is shown in Figure 4. 1994). while nonlinear optimisation can predict co-contraction of pairs of antagonist twojoint muscles. inverse static and inverse dynamic optimisation (Winters.11. to date.g. Furthermore. The optimisation approaches discussed above are either static (and hence solved only once) or solved independently for each sample interval during a movement.
For example. Comparisons of the results of studies that do and do not incorporate muscle dynamics (Herzog. 1987a.b) suggest that.13) where is the normalised muscle active force.13 with Figure 4. which was developed to an optimal control model by Chow and Jacobson .. The solution of the force distribution problem has been hampered by a lack of reported quantitative musculoskeletal anatomy and analyses of the estimation of individual subject data by suitable scaling (e.g. for example. which will be considered in more detail in the second part of this book. Kaufman et al. 1991) or in the cost functions (e.13). Happee. This has been partially rectified by. The equations of forward dynamics.b).. but the precise muscle models needed and the difficulties of obtaining data in vivo on muscle properties of sportsmen and sportswomen remain to be resolved. Nubar and Contini (1961) proposed the minimum energy principle for static muscular effort. the inequality constraint then incorporates the physiology of the muscle based on its length–tension and force– velocity characteristics. 1981b). Kim and Pandy. 1991). In the former case.12 Prediction of co-contraction of a pair of antagonist two-joint muscles (after Herzog and Binding.Muscle forces and inverse dynamics 131 Figure 4. for the high contractile velocities and large ranges of movement that occur in sport. can also be used to determine muscle and joint forces (e. Pierrynowski (1995).9b). A unique solution can be obtained by minimising a (Kaufman et al. This will be. 1987a. muscle dynamics and activation possibly cannot be ignored. for example. Crowninshield and Brand. This occurred because the changes in force sharing during the step cycle and at different locomotor speeds were ignored in the optimisation models (also compare Figure 4. 1993). in the form: (4.g. 1994. 1993) predicted (lines 1–5) and measured (loops E) forces reported by Herzog and Leonard (1991) did not agree (Figure 4. is the normalised muscle passive force and a represents the upper bound of the activation of the muscle.g.g. These effects have been incorporated in the inequality constraints (e. Herzog.
13 Measured loops in muscle force curves at increasing locomotory speeds (a-c) compared with predictions using various cost functions (1–5) (after Herzog and Leonard. however. 1991) (1971). such as the sports performer. . particularly for three-dimensional models of multiple-segment systems.132 Calculating the loads Figure 4. The complexity of forward dynamics optimisation is. great.
1993). and some success with validation has been reported (for example. Allowance is also usually made for instantaneous muscle length and velocity. This method estimates the active muscle force as the product of the EMG signal. and the approach rarely predicts moments about the three axes that equal those measured (McGill and Norman. of the neural control of muscle coordination and the mechanical factors of joint angle and its rate of change. Obviously more research is needed into why the central nervous system apparently cannot fully activate muscle in an MVC (Enoka and Fuglevand. In both these approaches. the EMG signal is usually normalised to that for a maximum voluntary contraction (MVC) to partition the joint reaction moment. Limitations exist in the use of the MVC as a valid and reliable criterion of maximal force for normalisation (summarised by Enoka and Fuglevand. 1994). muscle length and force factors and the slope of the muscle force-EMG relationship between 60% and 70% maximal efforts. 1993). 1991. no successful EMG-to-muscle tension predictions have yet been reported for a fast sporting activity. Although important strides have been made in this respect for isometric and some voluntary dynamic contractions (e. Caldwell and Chapman. contraction type and passive elasticity (e. Force estimations from EMG are difficult for deep muscles. The inability of some high threshold motor units to sustain activity also suggests caution in interpreting motor unit activity in the MVC as maximal. Furthermore. McGill and Norman. 1987). Furthermore.g. for example. the substantial EMG variations at constant maximal force suggest (Enoka and Fuglevand. Further difficulties are evident. Many of the above limitations also apply to the use of EMG to predict muscle tension. reported motor unit discharge rates of 20–40 Hz during an MVC are inconsistent with those needed to elicit the maximal tetanic force in all motor units of a muscle (80–100 Hz for a fast twitch motor unit). in an MVC.3. These include the standardisation. To overcome these. 1993) that the EMG is not a direct index of the magnitude of the neural drive to muscles at the high forces that occur in much sporting activity. 1993). Practical difficulties—of pain. (1995) devised a scaling method that does not require an MVC..Muscle forces and inverse dynamics 133 4. 1994). see Gregor and Abelew. 1993). fear of re-injury and motivation—also arise in eliciting MVCs from previously injured subjects. Frazer et al. Difficulties also arise from reported variability in the electromechanical delay with movement pattern and speed (Gregor and Abelew. This approach allows for co-contraction.g. which could confound interpretation of the results. Hof et al. in the different shapes of the ‘loops’ in the muscle force and EMG .3 USE OF EMC TO ESTIMATE MUSCLE FORCE Inverse optimisation models that use EMG as an index of muscle activation have some similarities with other approaches that incorporate the use of EMG records.
. the continuous synergy of all agonists predicted by non-linear cost functions (Denoth. 1968). a predicted muscle force is compared with the existence or otherwise of an EMG signal for that muscle. To investigate further the effect of the joint contact force on the stress distribution in the bone.4 Determination of ligament and bone forces If muscle forces can be estimated accurately.g.14. Beaupré and Carter. Although such information may appear to provide some subjective validation of the force distribution solution. 1988) can be evaluated.. 1989). 1992. 1984). equations 4. One such assumption might be that no force was present in the ligament during its slack period (Morrison.4) can be used to calculate the joint contact force (Fj) if an assumption is made about the passive. limitations arise because of some of the factors discussed earlier in this section. For example.134 Calculating the loads Figure 4.14 Muscle force loops (a) compared with IEMG loops (b) (after Prilutsky et al.. such as that bone is isotropic and homogeneous. Ranu. are suspect and the validity of many model results have not been assessed (King. the ligament force could be calculated from stiffness values assigned to that ligament when not slack (Wismans et al. ligamentous forces (Fp). 1994) curves for the soleus plotted against the gastrocnemius (Prilutsky et al. which has limited the use of such modelling methods in sports injury. finite element modelling is often used (see. In this approach. then the inverse dynamics equation for forces (e. the EMG signal has also been used to validate the predicted temporal pattern of muscle activation. 1980). shown in Figure 4.g. Alternatively. This is mainly because of a lack of data on material properties of biological material. The assumptions of some finite element bone models. . When calculating muscle force distribution. e. 4. 1994).
Jelen (1991) sought to calculate the patellar ligament force which had caused rupture. Using a frame rate of 54. including joint friction.2 Hz. 4. These angles are difficult to measure and so these are somewhat hypothetical values. which the author justified by a reportedly zero vertical hip acceleration in this phase of the movement.16).Estimation of a load causing traumatic injury 135 Not surprisingly. including quadriceps femoris. in comparison with the force in the quadriceps femoris and patellar ligament. Ignoring all other muscle and soft tissue forces and moments at the knee. That the moment arm for the patellar ligament force about the knee joint (OD in Figure 4. few examples have been reported of the estimation of tissue forces in a traumatic injury. based on previous data from their university and the cine analysis. The author showed the inclusion of joint friction to affect the patellar ligament force by only a couple of hundred newtons. • The setting of the thigh. The angles ß and are 20° and 0° respectively. when one of the lifters suffered a rupture of that ligament during the jerk stage of the clean and jerk Olympic lift (stage 5 of Figure 4.27 m. and all superior segment. The assumptions made by the author included the following. 1984). During this stage of the jerk.16) was 75 mm for the measured knee angle of 106°. and typical planar film analysis procedures.15). An example in which the load that causes the injury has been estimated is provided by the study of Jelen (1991). personalised to the lifter’s mass. The latter also gave a moment arm for the forces tending to flex the knee joint (AO in Figure 4.5.1 PATELLAR LIGAMENT RUPTURE Jelen (1991) was filming a weight-lifting competition to calculate the forces in the patellar ligament. the lifter lowers the bar by eccentric contraction of the relevant leg muscles. before an upward drive in which the same muscles contract concentrically. Angle d is the angle between the quadriceps femoris force vector • • • • .16) of 0. Angle ß is the angle between the patellar ligament force vector and the line normal to the line joining the instantaneous axis of rotation of the knee to the attachment point of the patellar ligament to the patella (OB in Figure 4.5 An example of the estimation of a load causing traumatic injury 4. accelerations to zero. The weight of the bar and the accelerations involved can result in large muscle and tendon forces. Use of anthropometric mass fractions from the literature (Ulbrichová.
15 Photographic sequence of the jerk stage of a clean and jerk Olympic lift during which rupture of the patellar ligament occurred (reproduced from Jelen. with permission). and the line normal to the line joining the instantaneous axis of rotation of the knee to the attachment point of the quadriceps femoris to the patella (OC in Figure 4. from simple measurements. 1991. and for reasons not stated by Jelen (1991).5 kN.16). The normal procedure at this stage would have been to obtain the ligament cross-sectional area. but possibly because the ligament was . Under these assumptions.136 Calculating the loads Figure 4. Jelen (1991) was able to calculate the ultimate strength of the patellar ligament (at which rupture occurred) to be close to 14. and to estimate the ultimate tensile stress and compare it with published values. Instead.
This was used to estimate the cross-sectional area of the ligament at 240–250mm2. Jelen (1991) concluded that the ultimate stress of the ligament might have been affected by the use of steroids. From this. the ultimate tensile stress was taken to be 60 MPa. ruptured.Estimation of a load causing traumatic injury 137 Figure 4.16 Knee model used for calculation of force in patellar ligament (after Jelen. a value reported previously for the Achilles tendon. 1991). The lack of comprehensive data on the . overload of the motor apparatus or administration of the drug Kenalog. but without explaining why.
1 and 4.5.g.2 CONCLUDING COMMENTS Whichever method is used to estimate muscle or other tissue forces. 4. with an angle of pull of 90°.17a is a free body diagram of a static non-horizontal single body segment (e. and the limitations which exist even when this information is available. a) Show that the force and moment equations for this segment are: Fjx-Fm sin =0 Fjy+Fm cos -m g=0 rmFm-(r cos ) m g=0 . The equations for planar force and moment calculations from inverse dynamics. for single segments or for a segment chain. 4. along with how the procedures can be extended to multiple-segment systems. Zernicke.2 to arrive at an inverse dynamics model of forearm flexion.2. 2. Such predictions of injury require far more multidisciplinary research into tissue mechanical properties and their response to exercise (e. the combined forearm-hand segment flexing about the elbow) with one muscle.7 Exercises 1. The chapter concluded with a rare example of muscle force calculations from a cine film recording of an activity in which an injury occurred.138 Calculating the loads ultimate tensile strength of human tissues and the effect of load rate is one limitation on the use of results such as those obtained from this study by Jelen (1991).2. List and describe any other simplifications that you consider the model to contain. as considered in Chapter 1. List and evaluate the simplifications made in sections 4. The uses and limitations of EMG in estimating muscle force were outlined. even accurate values do not alone predict whether an athlete would be injured or not. including typical simplifications made in inverse dynamics modelling. The method of inverse optimisation was covered. The various approaches to overcoming the indeterminacy (or redundancy) problem were described. 4.6 Summary In this chapter the difficulties of calculating the forces in muscles and ligaments arising from the indeterminacy problem were considered. Figure 4. and attention was given to an evaluation of the various cost functions used. 1989).g. were explained.
or angle of pull. (b) dynamic version of same problem. of 90°.05 m) from the joint with an angle of insertion. (ii) verify the answer using a force polygon.17b shows the centripetal and tangential accelerations for the same body segment during a movement with angular acceleration .Exercises 139 Figure 4.17a.17 (a) Static forces on non-horizontal single segment with one muscle.14m) from the elbow joint. (i) calculate the muscle force and the components of the joint force. b) The mass of the forearm-hand segment of an athlete is 2 kg and the centre of mass of the combined segment is 14cm (0. c) Figure 4. If the forearm-hand segment is stationary and at an angle ( ) of 30° to the horizontal as in Figure 4. Flexion is assumed to be performed by a single muscle that inserts 5 cm (0.
6: explain the limitations of these models of the pelvic and pectoral girdles.b. Show that the force and moment equations for that segment are: Fjx-Fmsin +m r( 2 cos +a sin )=0 Fjy+Fm cos -m g-m r(.140 Calculating the loads and velocity as indicated. Flexion is assumed to be performed by a single muscle that inserts 5 cm (0.17b. a) For the equations in section 4.09 kg·m2. Write the moment equations for both segments. if needed.5 rad·s-1. If the forearm-hand is instantaneously at an angle ( ) of 30° to the horizontal as in Figure 4. 3. If you have laboratory software and hardware that allows you to calculate forces and moments from inverse dynamics.4.2. The moment of inertia of the combined forearmhand segment about the elbow joint is 0. 7. a procedure for calculating the forces and moments at each joint in this planar representation of the runner. 5. Obtain. Assume the movement to be planar. if ground reaction forces were not measured. then perform such calculations for the ground contact phase of running.2 sin +a cos )=0 rmFm-(rcos )m g-Io a=0 d) As in example (b). Explain any differences between the joint reaction force components and the actual joint force components in exercise 2. b) Draw the joint reaction force and moment equivalents of Figure 4. with the use of clear diagrams. Explain the physical meaning of each of the terms in these equations. Draw a free body diagram of a two-segment kinetic chain. describe. Explain. Explain these graphs in conjunction. calculate the muscle force and the components of the joint force. calculate the joint reaction moment and force components. . 6.5 rad·s-2 and angular velocity of 2. if possible. with graphs of simple segment kinematics. 4.14 m) from the elbow joint. as in Figure 4. the mass of the forearm-hand segment of an athlete is 2 kg and the centre of mass of the combined segment is 14 cm (0.05 m) from the joint with an angle of insertion of 90°. After consulting the relevant further reading (section 4. compare and evaluate the methods for overcoming the indeterminacy (redundancy) problem. graphical representations of the forces and moments at a couple of the more important joints for this movement. with an anticlockwise (positive) angular acceleration of 1.17a. Draw a sagittal plane view of a runner during ground contact. A frontal plane view of this activity might use rigid triangular models of the pectoral and pelvic girdles. clearly state the indeterminacy problem and why it makes the estimation of muscle and ligament forces difficult. In each case.9).
K. (1997) Introduction to Sports Biomechanics. 4. muscle fatigue or minimum compression. 10.E. London.R. (1978) Human motion in space analyzed biomechanically through a multi-link chain method. V.F. K. Crowninshield.E. England.C. Champaign.-P. 21. R. IL. R. England. Comment on some of the general difficulties with the inverse optimisation approach. 59–66.Blanchi). (1995) Euler’s and Lagrange’s equations for linked rigid-body models of three-dimensional human motion.F. Describe the limitations on the use of EMG to estimate muscle force. USA. 100.9). Journal of Biomechanical Engineering. the ‘soft-saturation’ criterion. 239–306.S. A. You will probably find van den Bogert (1994) or Herzog (1996) useful for answering this question (see section 4. D. (1992) Finite element analysis in biomechanics. Journal of Biomechanics.-P. Bartlett.H. Journal of Biomechanics. Mathematical Biosciences. (1997) Error analysis. (1988) Biomechanical model calculations of muscle contraction forces: a double linear programming method. Briefly explain how Jelen (1991) estimated the force in the patellar ligament from a cine film record of the jerk stage of the clean and jerk Olympic lift. 10. 429–441.B. and evaluate.Blanchi). Kaufman. Human Movement Science.Y.A.Stokes and J. G. Oxford University Press. quadratic functions. An. J. (1981a) A physiologically based criterion of muscle force prediction in locomotion. Chaffin. The British Association of Sport and Exercise Sciences. England. K. in Three-Dimensional Analysis of Human Movement (eds P. C. pp. E.A. (1978) Use of optimization techniques to predict muscle forces.Bartlett). 9. (1991) The general distribution problem: a physiological solution which includes antagonism. (1995) Estimation of muscle and joint forces.Biewener). Human Kinetics. Challis. 145–175. Beaupré. in Biomechanical Analysis of Sport and Exercise (ed. S. 10. Human Kinetics. in Biomechanics Structures and Systems: a Practical Approach (ed. G.M. D. J. 13. and Jacobson. List. pp. and Chapman.A. J. (1971) Studies of human locomotion via optimal programming. Journal of Biomechanics.8 References . Summarise the limitations for sports movements of the following cost functions: linear functions. Leeds. D.M. 105–124.G.A. and Zatsiorsky. Stokes and J. R.References 141 8. 355–392. 149–174. pp. Crowninshield. and functions incorporating muscle dynamics.B. 793–801. Chaffin.. 201–214. Andrews.M. IL. I. (1969) Computerized biomechanical models: development of and use in studying gross body actions. D. Bean.-N. 88–92. I. 14. Champaign. and Schultz. pp. 2.D.. A. Chow.-S. A. Caldwell. functions supposedly relating to muscle energy. in Three-Dimensional Analysis of Human Movement (eds P.D. USA.B. R. Journal of Biomechanics. Aleshinsky.Allard. R. and Brand.R. and Carter. and Chao. Oxford.Allard. the assumptions made in his analysis. 455–458.Y. E & FN Spon. Explain the uses of inverse optimisation.
Norman. Journal of Biomechanics. Gregor.M. M. in Exercise and Sport Sciences Reviews—Volume 9 (ed. A minimum fatigue criterion for load-sharing between synergistic muscles.. Enoka. R.J. R. 953–960. Gregor. (1985) An hypothesis for the role of the spine in human locomotion: a challenge to current thinking. (1996) Force-sharing among synergistic muscles: theoretical considerations and experimental approaches.142 Calculating the loads Crowninshield. 173–202. 201–218. 17. 8–33.G. 82–87. in Exercise and Sport Sciences Reviews— Volume 24 (ed. J.D.Grabiner). J.O. USA.. pp. Lees. M. 83–95. Frazer. IL.I. (1986) A bioengineering analysis of human muscle and joint forces in the lower limbs during running. pp. P. and Johnson. (1993) Cocontraction of pairs of antagonistic muscles: analytical solution for planar static nonlinear optimization approaches.Miller).B. (1993) Skeletal muscle mechanics and movement. W. Herzog. (1987a) Individual muscle force optimizations using a non-linear optimal design. Harrison. and Abelew.J. S.Komi and A.Häkkinen..D. 17. P.Keskinen. (1993) Neuromuscular basis of the maximum voluntary force capacity of muscle. R.A. Free University Press. Herzog.Huijing and J. Journal of Sports Sciences. University of Jyväskylä. Amsterdam. 128–141. and Binding. W. W. 72–78. M. J. M. M. MD.A. Human Kinetics. Finland. pp. pp.J. .de Groot. Johnson. Journal of Biomechanics. R. M.. 195–199. Champaign. 4. in Current Issues in Biomechanics (ed. Baltimore. International Journal of Sport Biomechanics. (1978) Determining muscle forces in the leg during normal human walking—an application and evaluation of optimization methods. Happee. 284–285.van Ingen Schenau). M. and Townsend. and Rowe.Mero). in Current Issues in Biomechanics (ed. Shiavi. Journal of Biomedical Engineering. K. P. 21. and McGill..A.N. pp. D. in Current Issues in Biomechanics (ed. Champaign. R. pp.M. Dul. On criteria for load sharing between synergistic muscles.J. (1993) Ligamentous mechanoreceptors and knee joint function: the neurosensory hypothesis.. G.Grabiner). 3. (1984b) Muscular synergism— I. (1987b) Considerations for predicting individual muscle forces in athletic movements. (1984a) Muscular synergy— II. 663–673. (1994) Tendon force measurements in musculoskeletal biomechanics. Williams & Wilkins. R. in Biomechanics XI—A (eds G.. IL. Grabiner). USA. Champaign.V. P.D. R.E.W. Gracovetsky. Dul. Herzog.D. 215–235. (1981b) The prediction of forces in joint structures: distribution of intersegmental resultants. Human Kinetics. R. Grabiner. Sport Science Review. J. 167–179. (1994) Inverse dynamic optimization including muscular dynamics. 7. Townsend.Hollander. 205–216.A. pp. Journal of Biomechanical Engineering. 27. a new simulation method applied to goal directed movements. D.D. USA. 675–684.A. R. A. W. W. The Netherlands. 118. G. 159–181.L.B. Journal of Neuroscience Methods. and Fuglevand.Holloszy). 237–254. A. (1995) EMG to muscle force calibration in dynamic movements. McCullagh.E. USA. Shiavi. Denoth. Washington.P. Journal of Biomechanics. IL. 100. Franklin Institute. T. 3. and Brand. Mathematical Biosciences. Herzog. S.J.E. DC. A. Human Kinetics. (1988) Methodological problems in prediction of muscle forces. in XVth Congress of the International Society of Biomechanics Book of Abstracts (eds K. USA. Hardt. R.
A. P. T.Grabiner). Journal of Mechanical Design. Journal of Biomechanics.Corbin. IL. pp.V. McGrawHill. Champaign. pp. 781–792. John Wiley. 33–46. in Three-Dimensional Analysis of Human Movement (eds P.N.J. (1990) Relevance of in vivo force measurements to human biomechanics. McLaughlin.. 151–161. N. R.Landers.D. 97–104. (1980) Techniques for the evaluation of loads on the forearm prior to impact in tennis strokes. McGill. Mathematical Biosciences. Morrison. 29. D. IL. Y.A. (1978) Optimization of muscle-force sequencing in human locomotion. in Current Issues in Biomechanics (ed. USA. Pronk. Norman. (1991) Validation of optimization models that estimate the forces exerted by synergistic models.R. King. Bulletin of Mathematical Biophysics. M. Pierrynowski. in Biomechanics of the Musculo skeletal System (eds B. (1991) Biomechanical estimate of output force of ligamentum patellae in case of its rupture during jerk. and Contini.Nigg and W. A. Human Kinetics.M. (1993) A two-dimensional dynamic model of the human knee joint.R. K.M. 31–39. USA. C. in Future Directions in Exercise and Sport Science Research (eds J.Y. T.. IL. Journal of Biomechanics. Theoretical prediction. 27. Journal of Biomechanics. Kaufman. England. S.B.I. Herzog. properties and kinematics.S. R.-P. et al. (1994) Mathematically indeterminate solutions. V. USA. K. Litchy. John Wiley.). 40. (1994) Force-sharing between cat soleus and gastrocnemius muscles during walking: explanations based on electrical activity. Berlin.A. (1984) A review of biomechanical models. (1985) Dynamics: Theory and Applications. M. and Norman.A. Acta Universitatis Carolinae Gymnica. I. (1995) Analytical representation of muscle line of action and geometry. C. . 377–391. W. (1989) A barrier to understanding human motion mechanisms: a commentary. 215– 256. Herzog. in Studies on the Anatomy and Function of Bones and Joints (ed. 23(Suppl. 38. and Binding.Evans).-N.V. 701–710.R. E. pp. D. 14. 69–120. MacConaill.. Chichester.R. and Miller. and Leonard. (1968) Bioengineering analysis of force actions transmitted by the knee joint. and Levinson.L.Herzog). Springer.Stokes and J.Blanchi). R. 1223–1235. USA. B.M. J. An. 27.References 143 Herzog.Skinner. 102.A. 392–471.Nigg and W. Nubar. Bio-Medicine Engineering. 24(Suppl. T. (1994) Mathematically determinate systems. P. (1993) Low back biomechanics in industry: the prevention of injury through safer lifting.Allard. Human Kinetics. pp. 23. J. 3.L. 164–170. S.A. (1967) The ergonomic aspects of articular mechanics. Kane.I. Champaign. Human Kinetics.M. 71–82. 69–80. Journal of Biomechanics. L. pp.M.G. 472–491. (1987) A physiologically based criterion of muscle force prediction in locomotion.G. Prilutsky.Herzog). and Allinger. Biomedical Science and Instrumentation. and van Best. and Stark. 57–76. New York. Hof. W. A. 106.). Nigg. T.R. (1991) Physiological prediction of muscle forces—I. and Chao. 23–34. F. Journal of Biomechanical Engineering. W. Neuroscience. K. pp. Krishnan. 1).M. W.W. England. Jelen. Germany. Champaign.F. Pedotti. B. 793–801. Kim.. and Pandy. M.W. Chichester. in Biomechanics of the Musculoskeletal System (eds B.B. (1961) A minimum principle in biomechanics. M. Komi.
J.Holloszy). Baltimore. M. (1994) The future of performance-related sports biomechanics research. R. (1990) Human body segment inertia parameters: a survey and status report. pp. 413–416. Application to the study of human locomotion.F. in Biomechanics of the Musculoskeletal System (eds B.B.Holloszy). 23–51. Williams & Wilkins. Siemienski. Journal of Biomechanics. 163–186. . England. A. Schultz. an idea for load sharing between muscles. Italy. 187–230.Nigg and W. K. (1994) Analysis and simulation of mechanical loads on the human musculoskeletal system: a methodological overview.G. 9. 293–303. Zajac. Journal of Sports Sciences. F. in Exercise and Sport Sciences Reviews—Volume 18 (eds K. (1992) Soft saturation.Corbin. Rome. P.. USA.P. 293–303.Marchetti and V.-P. (1992) Soft saturation. and Fortney.Blanchi). 13. Baltimore. Spine.Yettram).Herzog). Journal of Sports Sciences. 11.. England. 12. MD. M. van den Bogert.. Application to the study of human locomotion. M.O.144 Calculating the loads Ranu.A. Promograph. Manchester.L. J. Baltimore. pp. (1995) Concepts in neuromuscular modelling. pp.Stokes and J. R. A. 3–32. D. 137–150. V. (1989) Movement dynamics and connective tissue adaptations to exercise. pp. Siemienski. A. 279–283. C. in Exercise and Sport Sciences Reviews—Volume 22 (ed. and Binding.E.Landers. USA. USA. Williams & Wilkins. USA. Champaign. Wismans. in Exercise and Sport Sciences Reviews—Volume 17 (ed. in Biolocomotion: a Century of Research Using Moving Pictures (eds A. (1989) The role of finite element modelling in biomechanics.J. Veldpaus.F. Promograph. Ulbrichová. pp. I.H.K.B. (1976) Investigations concerning the principle of minimal total muscular force. Unpublished doctoral dissertation. Zernicke. and Gordon. (1980) A three-dimensional mathematical model of the knee joint. MD. A. Chichester.). Manchester University Press. 4. pp.B. 76–82. in Material Properties and Stress Analysis in Biomechanics (ed. Williams & Wilkins. J.S. Yeo.L.Cappozzo. Rome. J. USA.M.R.Tosi). 472–491. Charles University. Journal of Biomechanics. F.Cappozzo. J. and Challis. in Biolocomotion: a Century of Research Using Moving Pictures (eds A. 225–241.L. and Anderson.M. Janssen.M.E.B. A. M. an idea for load sharing between muscles. providing the reader has enough mathematical background. in Three-Dimensional Analysis of Human Movement (eds P.B.Allard. (1984) Fractionation of body weight with respect to sports movement activities (in Czech). MD.Pandolf). Prague. in Future Directions in Exercise and Sport Science Research (eds J. W. 6. pp.Pandolf and J. Champaign. Yeadon. (1981) Analysis of loads on the spine.Marchetti and V. G. This is a good explanation of inverse dynamics modelling. 677–686. V. Human Kinetics. B. IL. M. (1993) Sport biomechanics 2000. H. IL. 257–292. and Jensen. pp. Winters.S.9 Further reading Herzog.J. Human Kinetics. J. (1989) Determining muscle’s force and action in multiarticular movement. Reid. et al. Skinner. et al. Italy. pp. John Wiley. This gives one view of inverse optimisation and an application to a sports movement without too much mathematics. (1994) Mathematically indeterminate solutions. Zatsiorsky.Tosi).
Baltimore. J.Further reading 145 van den Bogert. A.L. This provides a comprehensive review without complex mathematics. in Exercise and Sport Sciences Reviews—Volume 22 (ed. .J. (1994) Analysis and simulation of mechanical loads on the human musculoskeletal system: a methodological overview. USA. pp. 23–51. MD.Holloszy). Williams & Wilkins.
The functions of movement phases in terms of the biomechanical principles of coordinated movement are considered. linked to typical muscle activity patterns in several types of body movement. along with their applicability to various sports movements. The relationships that can exist between a performance criterion and various performance parameters are explained. A description and evaluation is provided of the limitations of kinesiological analysis for general sports movements. some modelling of the technique using statistics or mathematical models (Chapters 6 and 7). is the improvement of performance. as we observed in the introduction to Part One of this book. Introduction . with an emphasis on theory-driven statistical modelling and computer simulation modelling and optimisation. we shall focus only on the major way in which sports biomechanists try to enhance sports performance.Part Two Biomechanical Improvement of Sports Performance The second aim of sports biomechanics. that is by improving the technique of the performer. The chapter concludes with a brief consideration of open and closed kinetic chains. In Chapter 5. and the defects of the trial and error approach to technique improvement are covered. A method for the formal kinesiological analysis of sports movements is introduced and applied to various single joint and multi-joint sustained force movements. The importance of the phase analysis of sports movements is emphasised and illustrated with reference to ballistic movements and running. The cross-sectional. This can involve certain aspects of equipment design. we consider the fundamentals underlying the biomechanical optimisation of sports techniques. in this part of the book. other sports movements are touched on briefly. However. including a brief consideration of what coordinated movement is and how it is controlled. This usually involves analysis of the technique (Chapter 5). various aspects of biomechanical analysis of the movements of the sports performer are covered. and the feedback of the results to effect changes in the technique (Chapters 8). The biomechanical principles of coordinated movement—both universal and partially general— are covered. In Chapter 6. as was noted in Chapter 4.
a brief coverage is provided of the use of computerbased feedback and likely developments in this mode of information provision are outlined.148 Part Two: Biomechanical Improvement of Sports Performance longitudinal and contrast approaches to statistical modelling are described and the limitations of statistical modelling in sports biomechanics are evaluated. further consideration is given to the uses of computer simulation modelling in the biomechanical optimisation of sports techniques. . which has a simple performance criterion. Finally. An appreciation is provided of the important roles played by technique training and skill acquisition in the process of modifying a sports technique. The principles and process of hierarchical modelling are considered and illustrated using a hierarchical model of vertical jumping. are covered. Chapter 8 considers how the results of biomechanical studies of sports techniques can be communicated and fed back to the athlete and coach to improve performance. simulation evaluation and optimisation are also provided. simulation. The chapter concludes with a brief consideration of future trends in simulation modelling and the optimisation of sports movements. these are optimal javelin release and optimisation of implement radius in the hammer and discus throws. The advantages and limitations of computer simulation modelling. simulation. The interpretation and explanation of graphical representations of optimisation and the use of contour maps to identify likely ways to performance improvement are emphasised. when seeking to evaluate and improve sports techniques. Some aspects of simulation modelling of aerial sports movements are also covered. particularly their modelling. This is done by close reference to two published examples. The differences between static and dynamic optimisation and global and local optima are covered. The issues that must be addressed in seeking to optimise the provision of biomechanical information to the coach and athlete are discussed. brief explanations of modelling. The chapter concludes by evaluating existing models of human skeletal muscle and their use in both general computer simulation models of the sports performer and establishing optimal sports techniques. In Chapter 7. The strengths and weaknesses of the various technique assessment models and their limitations in feedback are described. The three stages of learning a sports technique are defined and the relevance of each to technique improvement is considered. The fundamental points that must be satisfied for biomechanical feedback to the coach and athlete to be relevant are covered. optimisation and simulation evaluation stages. Three models of human body-segment inertia parameters are compared and contrasted.
1 Principles of coordinated movement .Aspects of biomechanical analysis of sports performance 5 This chapter is designed to provide an understanding of various aspects of the biomechanical analysis of the sports performer. the CNS [central nervous system]. James and Brubaker (1973) wrote: ‘The execution of a patterned movement involves. we are concerned with the study of coordinated movement patterns. whereas at low skill levels the learning of coordinated movements is involved. in descending order. At skilled levels of performance. Bernstein (1967) considered coordinated movements to involve: ‘The mastery of redundant degrees of freedom within a kinematic chain’. an important concept to which we shall return. what features of these movements we try to study and understand. muscles. It is instructive at the outset of this chapter to consider what is meant by coordinated movement patterns. After reading this chapter you should be able to: • explain briefly how movement is controlled • define and evaluate critically the biomechanical principles of coordinated movement and their applicabilily to various sports movements • undertake a phase analysis of a ballistic movement of your choice and describe the fractions of each phase in terms of the biomechanical principle of coordinated movement • understand how phase analysis can be applied to other sports movements • undertake formal kinesiological analyses of various single joint and multi-joint sustained force movements and verify your analyses using electromyography (EMG) or palpation-observation • measure and explain the activity patterns in various types of body movement and in open and closed kinetic chains • describe and evaluate the limitations of kinesiological analysis applied to general sports movements. and a system 5. Sports biomechanics predominantly involves the study of sports skills. peripheral neurons. and why these features are chosen.
these being as follows. Higgins (1977) stated that it is necessary to understand the constraints imposed on the movement. flexibility. for the CNS to change the overall movement .1 illustrates a general model of the factors affecting the generation and control of a movement. However.1 can be expanded into that of Figure 5. The underlying control of movement must depend. Environmental: spatial and temporal constraints. torques. It is tempting to assume that coordinated movement is. Figure 5. Such constraints can also be considered to include rules and equipment. on its duration: movements in sport are usually fast. 5. Biomechanical: forces. This form of control is associated with higher levels of integrated behaviour than is possible with openloop control. then the control is open-loop. strength. etc. The generated movement pattern is compared with the desired response and necessary adjustments are made (feedback).2. Biomechanists are usually concerned with the observed characteristics of the movement. memory.’ Higgins (1977) considered that: ‘Integration of the movement combines the parts and elements into a whole. which relate to open and closed skills and fall within the domain of motor learning.1. A knowledge of the appropriate neuropsychology and neuroand muscular physiology is needed to understand fully the biomechanical features of a technique.150 Biomechanical analysis of performance of bony levers upon which the muscles can exert force. which shows both peripheral nervous system (PNS) and central nervous system (CNS) mechanisms. if no feedback loop exists. which is created subject to the constraints acting on and the complexity of the kinematic chains involved. etc. integrating CNS processes of sensory perception. The control diagram of the system of Figure 5. • • • Morphological: anatomical-anthropometric.1 HOW IS MOVEMENT CONTROLLED? To develop the ability to analyse movement biomechanically. to some extent. as in most effective inanimate control systems. to establish an order of priority among these features and to seek to improve that technique. we must have some idea of how human movement is controlled. information processing and effector mechanisms with the morphology…and environment. which are initiated by neural processes in the brain. inertia.’ These statements leave no doubt that the coordination of movement is a pivotal element of the sport and exercise sciences and is both multi-and interdisciplinary. a product of closedloop control (a servomechanism). Control performed with a feedback loop is called closed-loop control.
pattern. for example. with the muscle spindle receptors providing peripheral feedback. and the controlling mechanism could be obtained by reflex control through α-γ coactivation.Principles of coordinated movement 151 Figure 5. Peripheral control may be available to correct execution errors within a correct movement pattern. The process is coordinated by the CNS but controlled . not a possible mode of control for fast movements. The response time of the peripheral control system is 30–50 ms. ball behaviour that is slightly different from that expected might allow late stroke adjustments in bat and racket sports. This is. Figure 5. it could not be changed. If the wrong movement pattern was chosen.2 Feedback control systems. a minimum time of 110 ms (proprioceptive) to 200 ms (visual) is needed before the change is initiated. a batsman playing a shot to a very fast bowler in cricket. For example. therefore.1 Control of movement. This entails both the main (α) and intrafusal (γ) muscle fibres being activated simultaneously.
Although the mechanism of α-γ coactivation has been demonstrated in fairly slow movements..1. Noting that the analysis level may be qualitative or quantitative. Fine execution control is under the direction of the muscle spindle system.3 Types of structural analysis. which also involves other areas of sport science (Figure 5. we identify different types of observation and experimental methods in biomechanical and kinesiological analysis (Table 5.3). 1998). The central storage requirements of generalised motor programmes have been challenged in recent years. Williams et al.152 Biomechanical analysis of performance by the PNS. 5. Kelso. with what force and for how long. Figure 5.2 STRUCTURAL ANALYSIS OF MOVEMENT Experimental sports biomechanics can be described as the structural analysis and quantification (or measurement) of coordinated movement patterns. Schmidt proposed a generalised programme for a specific type of movement. for example an ‘overarm pattern’. it has not been proven as the control mechanism in fast movements. New theories of motor control have been proposed that place a greater emphasis on the coupling of perception and action and on information flow in the environment (e. in what order. 1976) of a motor programme of pre-structured commands as to which muscles act. .1). 1982. This leads to the idea (Schmidt. but then neither has any alternative. along with the necessary α and γ efferent activity.g.
the transfer of angular momentum between body segments is often proposed (section 5. For example.2) as a feature of vigorous sports movements. force. which are valid for all activities principles of partial generality. for example. 1981). valid for specific tasks. as illustrated by the equations for two-segment motion in Chapter 4. endurance and precision or accuracy tasks particular principles. 1996) have shown that.2 Biomechanical principles of coordinated movement It should be noted that. Instead. Putnam.1 Analysis features We can describe the biomechanical principles of coordinated movement as ‘general laws based on physics and biology which determine human motion’ (Bober. 5. valid for large groups of activities. the performance of the kick would be improved if the thigh did not decelerate. although the coordination of joint and muscle actions is often considered to be crucial to the successful execution of sports movements.. 1997a). 1983. These principles may be subdivided into: • • • universal principles. The scarcity of systematic research into the applicability of the principles of coordinated movement to sport should be borne in mind. angular momentum is not transferred from the thigh to the shank when the thigh decelerates.2. in kicking. too few of the underlying assumptions have been rigorously tested (Bartlett. several investigators (e.Biomechanical principles 153 Table 5. .g. S rensen et al. Its deceleration is caused by the motion of the shank through inertia coupling between the two segments. However.
1981) There is some evidence to support this as an adaptive mechanism in skill acquisition. in a basketball set shot the player keeps the elbow well into the body to reduce the redundant degrees of freedom. Minimisation of energy used to perform a specific task or the principle of limitation of excitation of muscles (Bober. which relates to the muscle’s length–tension curve. 1977). The temporal and spatial characteristics of the relevant kinetic chains are often the main focus of many quantitative biomechanical analyses. A simple kinetic chain from shoulder girdle to fingers contains at least 17 degrees of freedom. storage of elastic energy. Obviously many of these need to be controlled to permit any degree of movement replication. the reduction in unnecessary movements during the learning of throwing skills (e. 1977) The kinematic chain (now more commonly referred to as the kinetic chain.3 (phase analysis). This initial counter-movement is often necessary simply to allow the subsequent movement to occur. The underlying mechanisms of the stretch-shortening cycle and some of the unresolved issues for its importance in sports movements were considered in Chapter 2. The large number of multijoint muscles in the body supports the importance of energy efficiency as an evolutionary principle. a segment often moves in the opposite direction to the one intended: this is considered further in section 5.154 Biomechanical analysis of performance 5. . and stretching the muscle to optimal length for forceful contraction. Higgins. Other benefits arise from: the increased acceleration path. 1981) or the stretch-shortening cycle of muscular contraction (Hatze. 1981) or control of redundant degrees of freedom in the kinematic chain (Higgins. for example. Coordination of that chain becomes more complex as the number of degrees of freedom—the possible axes of rotation plus directions of linear motion at each joint—increases.2.1 UNIVERSAL PRINCIPLES Use of pre-stretch (Bober. The forces need to be applied in the required direction of motion.g. and this term will be used throughout the rest of the book) proceeds from the most proximal to the most distal segment. This principle explains why skilled movements look so simple. Principle of minimum task complexity (Bober. For example. initiation of the stretch reflex. 1983) In performing many activities.
such as a high jump take-off. It relates to the impulse-momentum equation: impulse=change of momentum= average force×time force acts. such as discus throwing. This principle relates to the generation and transfer of angular momentum.Biomechanical principles 155 5. In impulse generation. Principle of impulse generation-absorption This principle is mainly important in force and speed activities. in the recovery phase of sprinting. The sequence is continued by the faster muscles of the extremities. Minimisation of inertia (increasing acceleration of motion) This is most important in endurance and speed activities. In absorbing momentum. the former must predominate because of the explosive short duration of many sports movements. It involves the recruitment of body segments into the movement at the correct time. the hip is flexed with the knee also flexed. catching a cricket ball. e. This shows that a large impulse is needed to produce a large change of momentum. this configuration has a far lower moment of inertia than an extended or semiflexed knee. transfer of angular momentum along the kinetic chain) This principle is most important in activities requiring speed or force. In correct sequencing. which ensures that muscles are stretched to develop tension when they contract. this requires either a large average force or a long time of action. which not only have a larger range of movement and speed but also improved accuracy owing to the smaller number of muscle fibres innervated by each motor neuron (the innervation ratio).g. to maximise rotational acceleration. the time is increased by ‘giving’ with the ball to reduce the mean impact force. . preventing bruising or fracture and increasing success.2 PRINCIPLES OF PARTIAL GENERALITY Sequential action of muscle (summation of internal forces. which are usually pennate and which produce force to overcome the inertia of the whole body plus any sports implement. proximal segments move ahead of distal ones. serial organisation. Movements are generally initiated by the large muscle groups. For example.2. Movements at any joint should be initiated with the distal joints in a position that minimises the moment of inertia. which are affected by changes in the moment of inertia. which requires power—the rapid performance of work (see below).
In a quantitative analysis. a full temporal and kinematic description of the movement is obtained. such as the angle of release of a javelin.g. Qualitative analysis should uncover the major faults in an unsuccessful performance. possibly represented by a hierarchical technique model (Chapter 6). Quantitative analysis. • Qualitative analysis. which This principle arises from the work-energy relationship shows that a large change in mechanical energy (∆E) requires a large average force or the maximising of the distance (s) over which we apply force. 5. the method of inverse • .156 Biomechanical analysis of performance Maximising the acceleration path . 1997b). This is usually based on observation from video or cine film. Once stored in a computer.3 Temporal and phase analysis The biomechanical analysis of a sports technique can be categorised as follows (e. With the relevant body segment inertia parameters. This analysis involves a descriptive assessment of the observed technique and is usually conducted to determine if the technique is being performed correctly. It should be noted that these three levels of analysis fall on a continuum on which the boundaries are not always obvious. a shot-putter making full use of the width of the throwing circle. normally made with the use of a computer-linked coordinate digitiser. That is. for example. the data can be processed to give a variety of kinematic information. A quantitative analysis also enables us to study the key features of the movement and helps to define optimum performance parameters.2). On-line opto-electronic systems with automated or semi-automated coordinate digitisation are now increasingly used (see Bartlett. A good quality visual recording of the movement must be made and a freeze frame video playback machine (or cine projector) is required for making detailed measurements. whether the technique is in accordance with relevant general biomechanical principles and specific principles for that movement (section 5. in either real time or slow motion. Stability A wide base of support is needed for stability. Hay and Reid. 1982). where sudden changes in the momentum vector occur. This can be used to make a detailed assessment of the technique and to conduct objective inter. This is an important principle in events requiring speed and force. this applies not only for static activities but also for dynamic ones. this is the approach used by most coaches and teachers.and intra-individual comparisons.
but good. The later phases depend upon the previous phase or phases. throwing and kicking skills) can be subdivided into three phases: • • • Preparation (backswing) action (hitting) recovery (follow-through). because of the sheer complexity of many sports techniques. estimates of a few selected performance parameters are required. Each of these phases has specific biomechanical functions. Semi-quantitative analysis tends to be used either when the appropriate equipment required for quantitative analysis is not available. but linked. a suitable definition of the phase boundaries needs to be chosen. the legs and trunk will be in their action phase while the distal joints of the racket arm will not yet have reached the end of their preparation phase. This . • The first step in the semi-quantitative (or quantitative) analysis of a sports skill is often the timing of the duration of the phases of the movement. 5. The simple measurements usually include the timings of the phases of the movement (see below).g.1 PHASE ANALYSIS OF BALLISTIC MOVEMENTS Many ‘ballistic’ sports movements (e. this should always be borne in mind when undertaking any phase analysis of sports movements. For example. the essential feature of these movements is their wholeness. This is sometimes referred to as segmentation of the movement (e. Kanatani-Fujimoto et al. Each phase then has a clearly defined biomechanical function and easily identified phase boundaries. when recording the durations of these phases. It should be noted that. 1997). However. or when only simple.. Other simple measurements may include the range of movement of a limb. in a tennis serve the end of the backward movement of the racket might be chosen as defining the end of the preparation phase and the start of the action phase.3. often called key moments or key events.g.Temporal and phase analysis 157 dynamics can be used to calculate the net joint reaction forces and moments (see Chapter 4). hitting. The division of a movement into separate. at that instant. The phases of the movement should be selected so that they have a biomechanically distinct role in the overall movement which is different from that of preceding and succeeding phases. as in the phase analyses of the following subsections. phases is also helpful in developing a qualitative analysis of a technique. Although phase analysis can help the understanding of complex movements in sport.
Preparation phase This phase has the following biomechanical functions. it is then necessary to use the longest possible backswing consistent with other requirements. that is. • • • . while a long backswing will increase the tonic (position-dependent) response. a certain arbitrariness in the selection of the key events. it increases the acceleration path. as in a discus throw. then a short and slow preparation is needed to control both the phasic and tonic spindle output so as to produce only the small forces needed. This energy can then be ‘repaid’ during the action phase. then a fast backswing will gain the advantage of an increased phasic (speed-dependent) discharge. To make full use of the tonic response. this is evident in the cueing techniques of skilful snooker players. It allows the larger segments to initiate the movement (sequential action of muscles). while a minimum hesitation between the preparation and action phases will allow full use of the phasic response. • • • • It puts the body into an advantageous position for the action phase.2). It allows the storage of elastic energy in the series elastic and parallel elastic elements of the agonist muscles. It makes use of the length-tension relationship of the agonist muscles by increasing the muscle length to that at which maximum tension is developed (about 1. then the phasic response cannot be used. If accuracy is the main goal. It puts the agonist muscles on stretch (stretch-shortening cycle) ‘…thus increasing the output of the muscle spindle to reinforce gamma discharge and increasing impulse through afferent neurons to the motor pools of functional muscle’ (Gowitzke and Milner. 1980).158 Biomechanical analysis of performance is reflected in the principle of sequential action of muscles (section 5. A short hesitation at the end of the preparation allows the phasic response to subside to the tonic level and aids accuracy. This indicates one drawback of phase analysis. A fast backswing will promote a greater rise in spindle frequency leading to a stronger action. If the movement requires force or speed but the preparatory position must be held.2 times the resting length). It provides Golgi tendon organ facilitation for the agonists in the action phase by contraction of the antagonist muscles. If the requirement of the movement is force or speed. It maximises the range of movement of both the implement and of the performer’s centre of mass.
2 PHASE ANALYSIS OF RUNNING The obvious division of running into support and non-support phases does not provide an adequate biomechanical description of this activity. as at the end of a golf swing. all these principles should be evident. Finally. It is characterised by a relative shortening of the overall limb length towards the lowest centre of mass position. Movements are initiated by the large muscle groups and continued by the faster smaller and more distal muscles of the limbs. 5. one or more principles may be of lesser importance. The accuracy of movement also increases through the recruitment of muscles with a progressively decreasing innervation ratio. redundant degrees of freedom are controlled. A better one is that of James and Brubaker (1973) who divided each of these phases into three sub-phases. Recovery phase This involves the controlled deceleration of the movement by eccentric contraction of the appropriate muscles.2) become evident here. In skilful performers. A position of temporary balance (stability) may be achieved. The segmental forces are applied in the direction of movement and movements are initiated with minimum inertia as the movement proceeds along the kinetic chain. this has often been described as the amortisation phase for some jumping activities. whereas in force.3. we observe the sequential action of muscles as segments are recruited into the movement pattern at the correct time. the follow-through may require a conscious effort to overcome the Golgi tendon organ inhibition. where speed is usually the predominant requirement. The movements should be in accordance with these biomechanical features if the movement pattern is correct. . For a learner. In ballistic movements.Temporal and phase analysis 159 Action phase Many of the general biomechanical principles of coordinated movement (section 5. increasing the speed throughout the movement as the segmental ranges of movement increase. which is reinforced by antagonistic muscle spindle activity. Support phase • • Foot strike: the function of this sub-phase is impact absorption. accuracy or endurance movements. Mid-support: this serves to maintain forward momentum and to support the body’s weight.
this is characterised by a slowing of thigh (hip) extension followed by the start of thigh flexion. . Airborne phase to landing (airborne recovery). It is far preferable to treat each technique on its own merits. Effort is transferred from the powerful muscles of the trunk and thigh to the faster muscles of the calf. Hitting phase. Forward swing: although a preparation for foot descent. Landing: to control deceleration. and the latter assisting. knee flexion. • • 5. the main biomechanical function of this sub-phase is the enhancement of the forward and upward ground reaction thrust. Withdrawal: increase of acceleration path of javelin. Impulse drive: horizontal to vertical momentum transfer. Non-support (recovery) phase • Follow-through: functionally a decelerating sub-phase. Landing: impact absorption. Volleyball spike • • • • • • • Run-in: generating controllable speed. by the hamstrings. preparation for the next move. Foot descent: this begins with the arresting of the forward motion of the leg and foot.160 Biomechanical analysis of performance • Take-off: this has the function of accelerating the body forwards and upwards by a relative increase in the limb length (leg extension). and continues until the foot contacts the ground. This is necessary to reduce ‘braking’ and to provide an active landing allowing a smooth transition to foot strike. Airborne phase of preparation. The sub-phase begins as the foot moves forwards.3 PHASE ANALYSIS OF OTHER ACTIVITIES Examples exist in the literature of attempts to force the preparation-actionrecovery pattern on techniques to which it is not applicable. both accompanied by. Its main biomechanical function is to have the foot strike the ground with a backward speed relative to the body’s centre of mass at least as large as the speed of the mass centre relative to the ground.3. Javelin throw • • Run-up: generation of controllable speed. as in the following examples. this forward swing of the recovery leg coincides with the take-off sub-phase of the opposite leg.
2 Phases and sub-phases in swimming 5. it is not clear that the phases represent any important temporal events of motor behaviour. Table 5.Temporal and phase analysis 161 • • • Cross-over step. which is related to movement control.2. in technique analysis. see Bartlett and Best (1988) or Morriss and Bartlett (1996). Recovery. as above. For example.3. in future.4 CONCLUDING COMMENTS By splitting a complex movement into its temporal components (phases). which can then be used to identify incorrect features of the technique analysed. In some sports a phase-sub-phase analysis is more appropriate. Delivery stride: the action phase. Also. Kanatani-Fujimoto et al. This will usually be facilitated by some quantitative analysis of the technique.. muscle activation. For a detailed evaluation of the biomechanical functions of the phases of the javelin throw. Both the above techniques involve the ballistic preparation-action-recovery sequence as part of a more complex movement pattern.g. it is easier to conduct a qualitative analysis of the skill. However. that. that there is often an arbitrariness in the selection of the key events that form the phase boundaries. foot strike is often used as a key event in the walking or running cycle. An example for swimming is provided in Table 5. It should also be recognised. This suggests that. As previously mentioned. usually precedes this by as much as 100 ms. 1997). as the phases blend into a coordinated . It is left to the reader to identify the biomechanical functions of each of the sub-phases of this activity (see exercise 5). techniques for subdividing movements into more meaningful phases should be developed (e.
5. 5. such an analysis was based on the anatomical position of muscles. this still provides a useful first step for beginners. problems in the post-flight may be traced back to a poor generation of vertical or angular momentum during contact with the vaulting horse. in turn. scientific approach. and the complex kinetic chains involved. for example. often requiring the bone of one attachment to be stabilized many muscles cross more than one joint and their actions influence all joints they span the constantly changing position of body segments can alter the function of a muscle.162 Biomechanical analysis of performance whole. pectoralis major is a prime mover for extension of the humerus from above the horizontal but not from below the dynamic. Complicating factors are: • • • • the bi-or tri-planar actions of most muscles—this often requires neutralizers to prevent undesired movements muscles pull at both of their attachments. an apparent deficiency in technique in one phase may often be caused by an error in an earlier phase. • .1 AN APPROACH TO KINESIOLOGICAL ANALYSIS For an analysis of muscle activity to be valid. Although no longer accepted as a definitive description of muscle action in sport and exercise. result from errors even earlier in the vault. especially in sport. it is used in the context of this chapter to refer to the analysis of muscle activity and joint range of movement. it must involve a rigorous. Although the word ‘kinesiology’ has widely different interpretations. A study of (joint and) muscle activity might be thought useful in. fast nature of muscular contractions. in a gymnastics vault. without reference to detailed joint kinematics or kinetics. for example: • • • helping to estimate or calculate internal forces explaining or preventing injuries devising strength and mobility training programmes.4 Kinesiological analysis of sports movements It should not be necessary to argue the need for a thorough and reliable analysis of muscle and joint actions during the performance of sport and exercise movements. Traditionally.4. For example. This may.
Any measurements should be described.Kinesiological analysis of sports movements 163 Some aspects of these will be discussed later.2 A FORMALISED KINESIOLOGICAL ANALYSIS PROCEDURE The analysis method presented here is adapted from Rasch and Burke (1978).3 and 5. 5. using photos or sketches. usually representing transitions between phases. if EMG is not available. Close cross-referencing to the analysis sheet is necessary but should not be descriptive in nature. The description should preferably be pictorial. observation or palpation of the muscles can. an open mind is needed in case some important muscles have been omitted. Each phase should both require. Any kinesiological analysis should be supported by appropriate quantification of joint range of movement and muscle contractions (see Bartlett (1997b) for further details) such as: • • electrogoniometric. In the evaluation it is necessary to extract the implications of the analysis with respect to the rationale for the investigation. Evaluation Evaluate the movement on the basis of relevant criteria which closely relate to the objectives of the exercise. in some cases. Verbal anatomical descriptions may be used. provide a rough guide to which muscles are contracting. Analysis Analyse the joint and muscle actions of each phase using standard analysis sheets along with any quantitative data (see Tables 5. description in terms of separate muscle and joint actions. a joint protractor may be used for slow movements electromyographic (EMG) record of muscle contractions. Quantitative results lend power to the evaluation. Description Describe the movement and subdivide it into phases.4 and the comments above). . video or cine film record of range of joint movements. and be capable of.4.
3 Kinesiologiral analysis form .Table 5.
4 Kinesiological analysis form—brief explanation of column contents .Table 5.
in which case they can be omitted (the analyst should try to justify this). such as gravity. palpation or a comparison of columns 2.3 THE ANALYSIS CHART One analysis chart is used for each phase of the movement. contracting concentrically (C6). tend to extend (C3). adductors. Observed joint action (C2) This is obtained from precise inspection of the movement (this may be quantified). unless the movement is heavily resisted when the assistants are also introduced. such as gravity. Kind of contraction and kind of body movement (C6) This column combines the kind of contraction—concentric (+). All joints will not always be involved. for example. or by any combination of these. particularly gravity through the weight of body segments and external objects. flexion and if outside forces. . contracting eccentrically (C6). Only the prime movers are usually included. the flexors (C4).4. The following rules are often helpful for sustained force movements (C6). If the observed joint action (C2) is. Joint action tendency of outside forces (C3) This recognises the importance of outside forces. for example. then the muscle group active will be the agonists. then the muscle group active will be the antagonists. tend to extend (C3). eccentric (–). 3 and 6. This information is obtained from EMG. • If the observed joint action (C2) is.166 Biomechanical analysis of performance 5. except where the phase is irrelevant to the central problem. The various columns (C) are as follows. for example. • Specific muscles active (C5) Here we specify the individual working members of the active muscle group. such as flexors. gravity tends to extend the elbow throughout a dumbbell curl. Here the analyst states what the outside forces tend to do at the joint. the flexors (C4). Muscle group active (C4) The functional name of the muscle group that is contracting at this joint. extension and if outside forces.
Ballistic movement (BAL). the movement is designated SF+. Guided movement (GUI).Kinesiological analysis of sports movements 167 static (0) or relaxation (R)—and the kind of body movement. S1 (slight). as in tapping. Mod+ (increasing degrees of moderation). Oscillating movement (OSC) involves co-contracting antagonistic muscle groups alternating in dominance. These movements can be found in skills such as dart throwing. The three phases blend smoothly. the first phase of which is a sustained force movement (SF+). The following kinds of body. This group includes three subgroups. Passive movement (PAS) is a movement without continuing muscle contraction. where force is applied against a resistance by the contracting agonist muscles while their antagonists are relaxed. mediated oscillations to maintain balance as in stationary standing. Mod–. and the flight phase of a jump (horizontal component). as in a badminton smash. SF0. as in pairs events in ice dancing. Inertial movement (INER). These are obtained by observation or an EMG record or by comparison of other columns. if static. The movement can be fast or slow. or body segment. the vertical component of the flight phase of a jump. It ranges through 0 (none). The second phase is an inertial movement and the third is deceleration from eccentric contraction of antagonists (SF-) or from passive resistance offered by ligaments and stretched muscles. but not force or speed. Manipulation (MAN). Dynamic balance movement (DB) consists of a series of irregular. Max (great or maximum force). involves a continuation of a pre-established movement with no concurrent contraction of the agonist muscles. This is an important compound movement. Mod. as in the glide phase in basic breaststroke. Gravitational movement (GRAV) occurs in free fall. • Sustained force movement (SF). if eccentric. or coasting. strong or weak. If concentric. palpation or EMG. the armstroke in swimming and the initial leg thrust in sprinting. or tracking: agonists and antagonists are simultaneously active when great accuracy and steadiness are required. • • • • • Force of contraction (C7) This is estimated from observation. . for example. tennis serve and many typical movements in vigorous sport and exercise. SF-. This semi-quantitative scale is loosely related to that of Basmajian (1979). Examples include weight-lifting. where the movement is caused by another force or person. movement are recognised.
sustained force .168 Biomechanical analysis of performance Muscle group stretched (C8) A note should be made of which muscle groups are stretched by the exercise or movement. Comments (C10) These should be included on how undesired side actions are averted and any other important points. and are considered in the following section. This will show any flexibility benefits accruing from the movement or identify the initial phase of a stretch-shortening cycle.6. This is valuable to the student of the sport and exercise sciences.5. 5. In single joint. They do require more thought than the other columns. however. even for slow.g. particularly when supported by the use of EMG.5 Some limitations to kinesiological analysis 5. Basmajian and De Luca. The last two columns (C9 and C10) are extremely important and should never be omitted. sustained force movements. there are conflicting results between various studies and differences in muscle function between subjects (e.1 WHAT MUSCLES REALLY DO The ‘kinesiological analysis’ approach to the study of muscle action discussed in the previous section can provide insight into the roles played by muscles in the control and coordination of sports movements. Undesired side actions (C9) Those actions of the active muscles that are not wanted are noted here. The limitations of the approach are important. for example. 1985). This is certainly true of slow movements at a given joint to identify. especially when analysing single joint movements. even in these simple movements. 5.4 EXAMPLES The method outlined above provides a standardised and easy to use technique of kinesiological analysis of human movement.5. However. as shown by the example in Table 5. as in the examples of Table 5. elbow flexors and invertors of the foot. The analysis of multi-joint movements. However. matters are by no means as clear cut as a kinesiological analysis might suggest. the method should be studied very carefully and you should seek to become adept in its use. is more complex.4.
5 Kinesiological analysis form—examples .Table 5.
6 Kinesiological analysis form .170 Biomechanical analysis of performance Table 5.
4. . the movement is slow or resisted. (c) eccentric contraction of agonists. leading to classic patterns of concentric and eccentric muscle activity as represented in Figure 5.Some limitations to kinesiological analysis 171 movements. For multi-joint movements or Figure 5. (b) concentric contraction of agonists. so that accelerations are negligibly small. The muscle torque is then only required to overcome gravitational loads.4 Schematic representations of sustained force contractions: (a) concentric contraction of antagonists.
(b) agonist EMG. To Figure 5. . and acceleration (a). which are fast. Zajac and Gordon. velocity ( ). Except for the simple sustained force contraction. muscles function mainly as accelerators and the (somewhat simplified) results of Figure 5.5 would be considered typical for a single joint motion. as was seen in chapter 4 for two examples from the work of Zajac and colleagues (e. 1989). EMG tells us when a muscle is contracting—if we account for the electromechanical delay—rather than what the muscle is doing. (c) antagonist EMG.5 Single joint ballistic movement—schematic representation assuming no electromechanical delay: (a) angular displacement (θ).g. In ballistic movements.172 Biomechanical analysis of performance muscles. the positions of the joints and the moment arms of the muscles can cause complications.
. further detailed information on the kinematics of each of the segments in the kinetic chain and the forces and torques (moments) at the joints is needed. as in Figure 5. (b) moment (M–) from antagonists of proximal joint.Some limitations to kinesiological analysis 173 understand the latter more fully. by an antagonist muscle for example. Because of the closed nature of the chain.6 Open kinetic chain: (a) moment (M+) of agonists of proximal joint. This was seen from the equations of inverse dynamics in Chapter 4 and is discussed further in. This becomes increasingly complex as the length of the kinetic chain increases. It is far less likely that a pair of distal joint muscles could achieve the same effect. However. in theory. (c) transfers momentum to segment distal to the distal joint. one with a free end.2 OPEN AND CLOSED KINETIC CHAINS In an open kinetic chain. be accomplished by the concentric contraction of only the horizontal flexors of the shoulder joints. Zajac and Gordon (1989). but also on accelerations at other joints in the kinetic chain.5. although the muscles will still generate joint torques. needed at only two of the joints—a contralateral pair to produce symmetry—to achieve the required effect.6. 5. because of their weaker effect at the proximal joint.7). the bench press can. This obviously depends very much on the external load. The torques at any joint will depend not only on the accelerating effects at that joint by the muscles which cross it. and momentum is transferred along the chain. for appropriate loads. This is often associated with ballistic movements. it is possible for a distal segment to rotate without any muscle action at its joint with the rest of the chain. for example. Another complicating phenomenon is possible during sustained force movements in a closed kinetic chain (Figure 5. no joint can move independently of the others. Figure 5. and so active torques are. This can occur if the movement of a proximal segment is decelerated. at least in theory.
With reference to section 5. .7 Exercises 1. (b) end position.2. along with their applicability to various sports movements. 5.7 Potential muscle action (M) in a closed kinetic chain: (a) start position.6 Summary In this chapter various aspects of biomechanical analysis of the movements of the sports performer were covered. other sports movements were touched on briefly. Then. state whether they are relevant or not for groups of movements in which. without further reference to that section. The chapter concluded with a brief consideration of open and closed kinetic chains. both universal and partially general. For the principles of partial generality. force and accuracy are the dominant factors. A description and evaluation was provided of the limitations of kinesiological analysis of general sports movements. giving examples from sports of your choice. make a list of the biomechanical principles of coordinated movement. This included a consideration of what coordinated movement is and how it is controlled. 5. describe the meaning of each of the principles. linked to typical muscle activity patterns in several types of body movement.174 Biomechanical analysis of performance Figure 5. speed. The importance of the phase analysis of sports movements was emphasised and illustrated with reference to ballistic movements and running. respectively. The functions of movement phases in terms of the biomechanical principles of coordinated movement were considered. The biomechanical principles of coordinated movement—both universal and partially general—were covered. A method for the formal kinesiological analyses of sports movements was introduced and applied to various single joint and multi-joint sustained force movements.
seek to ascertain the accuracy of your analysis.1 and the simpler parts of Zajac and Gordon (1989) (the mathematics can be rather daunting unless you have an excellent mathematical background). or even just a good quality 50 Hz video camera and 50 Hz playback machine. repeat for a range of running speeds or runners of varying ability. Perform a full phase analysis (including the durations of each phase) from your own or commercially available video recordings of any ballistic sports movement.5. and try to explain. If possible. otherwise use an appropriate mixture of muscle palpation and observation of video recordings. From your knowledge of the biomechanical principles of coordinated movement. This will provide an example of an open kinetic chain (section 5. Then. ascertain whether the information contained in Table 5. 9.2). then use it to indicate muscle activity. running reasonably fast. if necessary. using Table 5.3. 7. If you have access to EMG. (b) Perform a full kinesiological analysis. If you have access to a motion analysis system. measure the duration of each of the six sub-phases of running described in section 5.4 and. of any other sustained force movement of your choice.3. the recommended further reading from Rasch and Burke (1978). 3. for the lowering phase. Without prejudice. 3 and 5) is correct. After reading sections 5.(a) Repeat exercise 6 for the information in Table 5. 8. using EMG if possible. or a video recording. Perform a kinesiological analysis. perform a kinesiological analysis of a ballistic single limb movement. 6. Be very careful to define sensible and meaningful phase boundaries.4? Account for any discrepancies. After careful study of section 5.6.5. 4. If you have access to EMG. 5. determine whether the descriptions of those sub-phases apply to your runner: account for any discrepancies. Account for any discrepancies.6. the raising phase of a barbell curl. do the muscle activity patterns you have recorded agree with the relevant examples of Figure 5.2. including measurements if feasible. There is often discussion of a speed-accuracy trade-off in some sports skills.4 and 5.Exercises 175 2. establish whether the muscle activity patterns resemble the simplified example of Figure 5. explain clearly what this trade-off entails. By qualitative analysis. for example the basketball free throw. prepare a full . Identify the biomechanical functions of each of the sub-phases of the three main phases of swimming (see Table 5. make a recording of a good runner. From your recording.2) for any of the four competitive strokes. any discrepancies between your results and the information in the three odd-numbered examples of Table 5.5 (examples 1.5. Note. such as a standing kick or overarm throw. If you have access to EMG.
(1996) Biomechanical factors critical for performance in the men’s javelin throw. New York. Morriss. R. 21. Lazareva.Kedzior and A. (1973) Biomechanical and neuromuscular aspects of running. Sports Medicine. Kelso. K. MD. Williams & Wilkins. B. Hay. and Burke. C. J. NJ. (1983) Computerised optimisation of sports motions: an overview of possibilities. Williams & Wilkins.A.J. R. USA.G.A. J. 477–486. R. H. Repeat for a range of loads or range of grip widths (or both if time permits).J. Journal of Sports Sciences. USA.. (1967) The Control and Regulation of Movement.S. Higgins. Do your results provide any evidence for the closed kinetic chain behaviour described in section 5. . Lawrence Erlbaum.A.M. IL. MD. Baltimore. record the activity in the triceps brachii and pectoralis major (sternal portion) muscles during a bench press at a load of 50% that of a single repetition maximum.5.H.Matsui and K. and Zatsiorsky. England. in Biomechanics VIII-B (eds H.Kobayashi).8 References Bartlett. (1985) Muscles Alive.V. pp.176 Biomechanical analysis of performance evaluation of the limitations of formal kinesiological analysis in the study of sports movements. If you have access to EMG. (1997a) Current issues in the mechanics of athletic activities: a position paper.2? Seek to explain any discrepancies. USA. MD. J. 688–694. pp. R. J. M. Rasch. PrenticeHall. (1982) Human Motor Behaviour: an Introduction. journal of Sports Sciences. 10. 30. England. (1977) Human Movement. 1–38. Basmajian.M. and Brubaker. 20–43. 5. J. Pergamon Press. 189–216. in Exercise and Sport Sciences Reviews—Volume 1 (ed. Kanatani-Fujimoto. USA. Mosby. Putnam.Wilmore). N.L. USA. USA. Human Kinetics. University Park Press. (1997b) Introduction to Sports Biomechanics.G. Journal of Biomechanics. R. J. and Milner. Hatze. Basmajian. USA. and Best. (1983) Interaction between segments during a kicking motion. Champaign.M. E & FN Spon. Hillsdale. London. methods and recent developments. (1981) Biomechanical aspects of sports techniques.J.E.K. K. Bober. (1978) Kinesiology and Applied Anatomy. Gowitzke.R. Motor Control. MD. 3–12. NJ. Bernstein. (1997) Local proportional scaling of time-series data: method and applications.M. 1. pp. James. Baltimore. P.Morecki. and Reid. (1988) The biomechanics of javelin throwing: a review. 438–446. K.Fidelus. PA. Lea & Febiger.V (1979) Muscles Alive. USA. 6. and Bartlett. (1982) Anatomy.M. Englewood Cliffs. C. R. C. J. Baltimore. Bartlett. St Louis. (1980) Understanding the Scientific Bases of Human Movement.Wit). USA. MO. B.V and De Luca. Bartlett. Mechanics and Human Motion. S. 1. Oxford. Academic Press. USA. T. in Biomechanics VII (eds A. Philadelphia. 501–509. Baltimore. V. C. an Integrated Approach. Williams & Wilkins.
Hutton).. PA. Journal of Sports Sciences. MD. in Exercise and Sports Sciences Reviews—Volume 4 (eds J. pp. 51–3. Rasch. This superb review of the role of muscles in kinetic chains highlights many of the limitations of the kinesiological analysis approach.A. It also demonstrates the difficulty of ascribing particular roles to particular muscles during movements as complex as those that occur in sport. and Gordon.Keogh and R. Williams & Wilkins. pp. F. this book is often available in university libraries. M.. A. USA.B. (1996) Dynamics of the martial arts high front kick. Journal Publishing Affiliates. 187–230.S. Chapter 18 and Chapter 3. Williams & Wilkins. and Williams. M.E. Zacho. P. Lea & Febiger. Zajac.9 Further reading . (1989) Determining muscle’s force and action in multiarticular movement. England.E. J.B. and Gordon.E. E. pp. USA. Davids. USA. K. Baltimore..B. (1978) Kinesiology and Applied Anatomy. Simonsen. (1976) Control processes in motor skills. 483–495. et.Further reading 177 Schmidt. CA. M. H. R. Williams. in Exercise and Sport Sciences Reviews—Volume 17 (ed.Pandolf). R. (1998) Visual Perception and Action in Sport.K.. pp. Santa Barbara. These chapters provide a classic account of the approach to analysis of muscle activity during sport and exercise movements. Zajac. K.Pandolf). E & FN Spon. SØrensen. Baltimore. F. in Exercise and Sport Sciences Reviews—Volume 17 (ed. Although now out of print. 14. 5. London. and Burke. 229–262. al.G.M. (1989) Determining muscle’s force and action in multiarticular movement. K. 187–230. Philadelphia.J. MD.E.
6. or ideal. technique. possibly. simulation evaluation and optimisation • appreciate and explain the differences between static and dynamic optimisation and global and local optima. After reading this chapter you should be able to: • sketch and explain the relationships that can exist between a performance criterion and various performance parameters • appreciate the defects of the trial and error approach to technique improvement • describe and compare the cross-sectional. longitudinal and contrast approaches to statistical modelling • evaluate critically the limitations of statistical modelling in sports biomechanics • understand the principles and process of hierarchical modelling construct a hierarchical model of any sports technique of your choice that has a simple performance criterion • appreciate the advantages and limitations of computer simulation modelling when seeking to evaluate and improve sports techniques • define and distinguish between modelling. both. An important element is the establishment of a theoretically correct. the reduction of injury risk or.6 Biomechanical optimisation of sports techniques This chapter will provide you with an understanding of the fundamentals underlying the biomechanical optimisation of sports techniques.1 Introduction An essential part of sports technique training is undoubtedly the identification and elimination of errors in the technique. simulation. . This process of establishing an ideal technique and using it to aid technique improvement poses three important questions. The emphasis will be on theory-driven statistical modelling and computer simulation modelling and optimisation. the aim of this being the improvement of the athlete’s performance.
If a linear relationship exists between the performance criterion and a biomechanical parameter (Figure 6. coach and performer. People involved in the coaching of sports techniques are frequently faced with the task of observing a performance and then offering advice about how that performance might be improved by technique changes. Theories about the best technique develop in an ad hoc fashion. providing that a logical cause–effect relationship exists (Hay et al. For example. sometimes. The relationship between the desired outcome of the technique. release angle and release height.3). as we shall see in Chapter 7. at the elite .The trial and error approach 179 • • • How is the ideal technique established and validated? How is it used in the investigation of changes in various aspects of the technique? How are the results fed back for implementation? The characteristics of a sports technique that contribute to the successful execution of that technique are obviously of interest to the sports scientist. However.1 are then replaced by n-dimensional surfaces (in the simplest case n=2 and they resemble contour maps. for example Figure 7. 6. and the participants (coaches. The relationships of Figure 6. the performance parameters include release speed.. There will also be performance parameters that have no correlation to the performance criterion (Figure 6. sports scientists) experiment with aspects of the technique and adopt those changes that improve the performance. In practice.c) then one should seek to improve that parameter at the performance level where it is most relevant.1b.1e). there exists an optimum value (v0) for that performance parameter (Figure 6. these performance parameters often interact to influence the performance criterion even when they are independent of one another. called the performance criterion (p). and the various performance parameters (v) are of vital interest (Figure 6. If the relationship is curvilinear (Figure 6. for any given athlete. then improvements in performance should result from improvements in the parameter at any level of performance. Much sports technique training evolves essentially through a process of trial and error. The nature of the relationship between performance parameters and the performance criterion may be of an ‘invertedU character such that.1d). 1976). coaches generally: • • • observe the performance and identify the technique factors that appear to limit it arrange these limiting factors in order of priority give advice to the performer based on the conclusions drawn.2 The trial and error approach This approach is clearly very subjective and errors may occur both in observation and interpretation. the performance criterion in the shot-put is the throw distance.1). where the slope of the curve is steepest.e. i. To achieve this. athletes and.1a).
and can possibly be linearised by using x=|v-v0| and seeking a function to linearise p against x. (b) is quadratic but can be linearised by x=log v.. typical of an optimal one. (e) is an inverted-U relationship.1 Different functional relationships between performance criterion p and independent variable v: (a) is linear. (d) shows no relationship between the variables. level of sport. identified by Dapena (1984). This essentially takes the technique of the top . this trial and error method of establishing an ideal technique is hazardous (Best et al. 1995).180 Biomechanical optimisation of techniques Figure 6. The second approach to technique improvement. is to copy the most successful individuals—the elite performer template. (c) is also non-linear but can be linearised using y=logp.
The correlation method essentially uses correlational statistics to ascertain the relationships between selected independent variables and the performance criterion. categorised as the crosssectional and the longitudinal. which should involve a sufficiently large sample for the results to be generalised (such as Bartlett and Parry. Failure to select a sufficiently wide group can lead to the omission of important causal parameters (Parry and Bartlett. sports science support to elite sport. 1984). This may identify both the variables that are important and their best values. The approach.3.. 1973) a single group is used. The former involves the analysis of a representative trial by each performer. Kunz (1980) found no significant relationship between take-off angle and distance in the long jump. for example. These approaches generally involve the collection and analysis of data from the performances of a large number of subjects of a wide ability. is used to identify variables that are significantly related to performance for a population of athletes represented by that given sample. Correlations between the performance criterion and various performance parameters. The data analysis will vary with the experimental design.. or as an adjunct to. 1984). are needed if we wish to change the performance of an individual. This type of modelling is often performed as part of. 6. For example. In the correlation method (Nigg et al. 1981). Two approaches are used for this type of analysis.1 TYPES OF STATISTICAL MODEL Several different approaches have been used to identify the features of a performer’s technique that influence the level of success achieved. This approach has been largely abandoned with the recognition that single athlete studies. The correlation coefficients are then used to deduce which performance parameters have an important influence on the performance criterion. What is also required is a more objective approach to identifying and prioritising the factors that limit the performance of a sports skill. force platforms. 1985). 6. and intercorrelations among parameters are established in a correlation matrix. This is essentially an empirical approach using high-speed cinematography. Often far too few trials or performers are analysed to allow conclusive results (for example. etc. the provision of useful information to the athlete and coach through. it is no more to be recommended than is the trial and error approach. Komi and Mero. preferably of a longitudinal nature.Statistical modelling 181 performers as the ideal one. we can identify the correlation and contrast methods (Hay et al.3 Statistical modelling .
Kunz (1980) showed that. when the fastest trial of each athlete was analysed cross-sectionally. as in Baumann’s (1976) study of three groups of female sprinters performing sprint starts. while the longitudinal approach does the same for a particular performer. longitudinal positive correlations were found between the maximum knee angular velocity in the recovery stride and running speed for all athletes in the study. It should also be noted that even a cross-sectional study will not always identify as important all those biomechanical factors of a technique that a correct biomechanical model would contain. for a group of 46 high jumpers and decathletes. which found a significant correlation between the horizontal velocity in the third last stride of the long jump run-up and the distance jumped for 12 finalists at the US national championships. the cross-sectional method seeks to establish the important determinants of performance for athletes in general. a study of 11 jumps by one of these athletes (Carl Lewis) showed no significant correlation.182 Biomechanical optimisation of techniques The longitudinal approach uses multiple trials by the same performer. An alternative to the correlation method is to divide the population into selected groups and use variational statistics to investigate the differences between the groups. Likewise. conclusions are reached concerning the important determinants of the performance criterion. significant correlations with the height cleared existed only for approach speed (positive) and contact time (negative) but not for the take-off angle. This was evident in the study reported by Hay et al. As an example. . longitudinal studies are far less common although there is now agreement that intra-athlete studies are crucial for the improvement of an individual’s technique. (1986). However. but this method is less frequently used. Comparing the two approaches. analysis of variance (ANOVA) or multi-variate analysis of variance (MANOVA). However. Other examples include the study by Bartlett et al. (1996) of three groups of javelin throwers and Müller et al. as in the study of 22 long jump trials by Mike Connolly reported by Hay (1985). It is worth emphasising that the results of a cross-sectional study cannot be generalised to a specific athlete nor vice versa. and providing that only causal variables are considered. no relationship was found. This approach seeks to identify significant variables for a population of trials for the same athlete represented by the given sample of trials. The two can yield different results. There are many examples of cross-sectional studies reported in the sports science journals. however. In this contrast method. the participants are usually divided into groups of contrasting ability. The means of the various performance parameter values are then computed for each group and the significance of the observed differences between the means are tested. A certain factor may appear to be an important determinant in a cross-sectional study but not in a longitudinal one. using t-tests. (1998) for skiers of contrasting skill levels. From the results obtained.
the effects of an uncontrolled constitutional (physiological. in fact. The arbitrariness. Fourthly.Statistical modelling 183 6. Thirdly.. random (type I errors). relationships between variables will occasionally be revealed that are. correlation matrices are reported but the relative importance of the variable contributions is not assessed. by using statistical techniques not in a ‘blunderbuss’ approach to fundamental theory building but for theory verification and refinement. Commonly. In a longitudinal study. Correlational statistics should never be used without first looking at a scattergram of the variables to ascertain the type of any relationship between them (Figure 6. but rather of its inappropriate. the relationship.g. for example. or take-off. 1997). anthropometric) variable can mask or inflate the importance of one or more independent variables. 1981.3. insufficient attention is often paid to the underlying assumptions of the statistical tests used. as. Mullineaux and Bartlett. This problem can be minimised. The following limitations are worth highlighting. when: • • • . 1997a. there is experimental control of the constitutional variables that distinguish athletes. However. Hay et al. from simple projectile motion considerations. is essentially quadratic so that it is speed squared that should have been chosen. However. This can lead to large overall type I error rates. Each variable partialled out drastically reduces the population to which the results can be generalised.2 LIMITATIONS OF STATISTICAL MODELLING Several limitations to the correlation and contrast approaches to statistical modelling have been identified (e. A second limitation relates to misidentification of the underlying relationships between independent and dependent variables. • In the first place. subjectivity and nonsystematic nature of some contrast and correlational designs are not an inherent feature of statistical modelling. if not avoided. This is despite the existence of sophisticated multiple linear (and non-linear) regression packages. speed and distance travelled. but a cross-sectional study exercises no such control. Problems arise here. This often arises when performance parameters are selected arbitrarily or not objectively prioritised. However. Bartlett. there are limits to and dangers in the use of this statistical control. or incorrect. statistical techniques are extremely valuable in the overall process. the most powerful statistical techniques are often not used. Judicious use of partial correlations can provide some statistical control—such as partialling out the performer’s mass if this appears to be a confounding variable (or covariate). for example.1). use. Furthermore. seeking correlations between release.
The collection and analysis of data over a large range of performers and a wide ability range. • The development of a theoretical model (usually referred to as a hierarchical model) of the relationships between the performance criterion and the various performance parameters. For a thorough discussion of these and related points. Such hierarchical models (e. see Mullineaux and Bartlett (1997). Furthermore. . a theoretical model of the relationships between the performance criterion and the various performance parameters is needed. 1997a).. Figure 6. (iii) multiple regression designs incorporate too few participants (or trials) for the number of predictor variables used. This considerably limits the scope for investigating the ‘what if questions that can provide great insight into a sports technique.g. investigators also frequently fail to report the power of their statistical tests or the meaningfulness of the effects that they find.184 Biomechanical optimisation of techniques (i) parametric statistical tests are used with small. This must be done ‘up front’ before any data collection takes place. 1981) helps to avoid the weaknesses that are too often apparent in the correlation and contrast approaches and ensures that the appropriate variables are measured and statistically analysed. (ii) no checks are made with ANOVA designs for normality and homogeneity of variance. the participation of the athlete is still needed to implement the changes and check whether they really are beneficial. unequal groups. • • To avoid the arbitrary selection of performance parameters and any consequent failure to identify the truly important relationships. if changes to a technique appear desirable from statistical modelling. It will also require careful observation and qualitative analysis of the technique. This model must be developed from theoretical considerations.3.2) identify the factors that should influence the performance outcome and relate them to the theoretical laws of biomechanics that underpin the movement (Bartlett. Hay and Reid (1988) suggested three steps in the development of a hierarchical model. • 6. Finally.3 THEORY-BASED STATISTICAL MODELLING The following three-stage approach (Hay et al. such as the biomechanical principles of coordinated movement (Chapter 5). The evaluation of the results with respect to the theoretical model.
2 Hierarchical model of a vertical jump for height (after Hay et al. consecutive parts to simplify the subsequent development of the model.2. The performance parameters included in the model should be mechanical quantities. They should be measurable (or sometimes categorical). For example. such as that in Figure 6. • • • The identification of the performance criterion—the measure used to evaluate the level of success in the performance of a sports skill.3 and 6.3). This can be ensured by using one of two methods (Figures 6. joint torques. 1976). time to swim a race=time spent starting+time spent turning+time spent swimming. are often used simply as a theoretical foundation for evaluating the techniques of individuals . Such subdivision is usually possible if the performance criterion is a measure of distance or time (see section 5. The identification of performance parameters: this involves identifying the factors that affect the performance criterion or subdivisions of the performance criterion. impulses of force.Statistical modelling 185 Figure 6. Hierarchical technique models. avoiding vague terms such as ‘timing’ or ‘flexibility’. The sub-division of the performance criterion: often it is useful to subdivide the performance criterion into a series of distinct. the long jump distance=take-off distance+flight distance+landing distance..4). They should be completely determined by the factors that appear immediately below them. such as velocities.
However. 1988). 1988). it was considered likely that segment positions etc.2 shows the theoretical model of a vertical jump proposed by Hay et al. The interrelationships between the performance criterion and performance parameters are reasonably straightforward here. Hay et al.’ . commented: ‘Whilst the precise nature of the factors and relationships that determine the magnitude of the vertical impulse was not known. (1976). or small groups of athletes. The maximum reach is the sum of the three heights proposed.3 Use of subdivision method in developing a hierarchical technique model (after Hay and Reid.3. The procedures used in constructing a hierarchical technique model and its use in statistical modelling are illustrated in the following subsection with the aid of an example. were among the factors of importance. That between the vertical speed and impulse comes from the impulse-momentum relationship. 6.4 HIERARCHICAL MODEL OF A VERTICAL JUMP Figure 6. It should be noted that the association between the height rise of the centre of mass and the vertical speed comes from the conservation of mechanical energy (the work-energy relationship). preferably using reasonably large samples of athletes or trials.4 Use of biomechanical relationship in developing a hierarchical technique model (after Hay and Reid.186 Biomechanical optimisation of techniques Figure 6. Figure 6. they should also be used to provide the necessary theoretical grounding for statistical modelling.
hip and ankle). The authors then produced a general performance model of striking simplicity. To evaluate their model.. 1981). They recommended a minimum of 150 subjects (n) to permit reliable multiple linear regression analysis and to overcome problems of collinearity among the p Figure 6. with time intervals as in Figure 6. It is also worth noting that one of the problems of multiple regression analysis occurs when the assumed independent variables are not.5 Revised hierarchical model of factors contributing to the vertical impulse (after Hay et al.8. Multiple regression analysis yielded the results shown in Table 6. All average joint torques and the duration of the selected time intervals were entered into a multiple regression analysis with H2 (height rise of the centre of mass). in fact. Hay et al. Contralateral joint torques (e. Hay et al. states that vertical impulses are generated by joint torque impulses.1981). to exist whenever a pair of variables within a given time interval had a correlation of greater than 0. and then developed as in Figure 6. To reduce this problem. independent but are themselves correlated. This new model simply: 1 2 3 breaks down the total vertical impulse into the sum of the impulses in several time intervals.. and was considered by Hay et al. but perhaps of limited use because of severe practical difficulties in accurately estimating joint torques in such kinetic chains (Hay et al. Hay et al. This problem is known as collinearity. (1981) addressed the important issue of choosing a suitable sample size for statistical modelling using multiple regression.g.Statistical modelling 187 In a later paper. (1981) used the same model down to and including the impulse row. expresses the joint torque impulses for each time interval as the product of the mean torque and the time interval.5. this was also the case for non-corresponding.1. . non-adjacent joints (e.g. (1981) analysed cine film of 194 male students. for adjacent segments the distal joint was disregarded. right and left elbow) were averaged and treated as one variable.6.
Table 6.188 Biomechanical optimisation of techniques Figure 6. be noted that few studies have been reported that have used such large samples.. 1992. 1995).9% of the variance in H2 (from Hay et al. n/p>10. Howell. 1981).. This recommendation is generally in agreement with those of other authorities (e. n/p>20. Although the authors did not emphasise the practical importance of their results. It should. Vincent.1 that an important body of information was obtained that could help in optimising technique. it is evident from Figure 6. however. 1981) variables.6 Joint torques for which the explained variance in H2 exceeded 2.g.1 Rank order of torques that accounted for more than 2.9% (after Hay et al. This is perhaps due to the difficulty of recruiting participants and the tendency .6 and Table 6.
Two related concepts are simulation (or computer simulation) and optimisation.7 The relationship between modelling. All other Figure 6. Donner and Cunningham. Mathematical modelling makes the link between the performer. A solution sometimes proposed to overcome these difficulties—combining participants and trials—is permissible only under certain conditions. and its motions. These will be discussed in subsections 6. 1997b. the models that are used to evaluate sports techniques are based on physical laws (such as force=mass×acceleration. in the context of specific examples.4 Mathematical modelling In mathematical modelling. simulation. 1984). in a unified structure (Figure 6.4. Modelling. the optimal technique. violations of these conditions can invalidate such a correlational design (Bartlett. It involves representing one or more of the characteristics of a system or object using mathematical equations. The art of modelling is often described as putting only enough complexity into the model to allow its effective and meaningful use. unlike statistical models that fit relationships to the data. simulation and optimisation encapsulate.7). the processes involved in seeking the values of a set of variables or functional relationships that will optimise a performance. or sports object. simulation evaluation and optimisation.1 and 6.4. Every model is an approximation that neglects certain features of the system or object. 6.2 and. in principle.Mathematical modelling 189 to base correlational studies around elite performers in competition. . in Chapter 7. F=ma). Mathematical modelling is also called deterministic modelling or computer modelling—the three terms are essentially synonymous. This can allow for the determination of optimal values of variables within a technique or.
Best et al. increases rapidly with model complexity.. they are not even feasible. For example. It is worth noting. and then only if this is necessary. Indeed such a model (see Best et al. so .4. One approach to simulation evaluation. that Hubbard and Trinkle (1992) used this model as the first step in their investigation of the optimal partitioning of take-off kinetic energy for the high jump and only introduced a more realistic model at a later stage (see subsection 6. the modeller should always start with the simplest model possible that captures the essential features of the movement being studied. the simpler the model the better as it is easier to understand the behaviour of the model and its implications. will be considered further in Chapter 7. simulation involves the performance of numerical experiments on these equations. these evaluations are not carried out. 1987). It is much easier to control external variables in a mathematical model than in the real world. Such a model would be of limited value. after which we transform the results back to the real system to understand reality.1 SIMULATION Experiments measure what happens in the real world to real objects: a mathematical model forms a similar basis for computer experiments.g. especially for feedback to coaches and athletes. Only after a full understanding of this simple model has been gained should the model be made more complex. The rigid rod representation of the high jumper might appear less convincing. in some. This model will be used in Chapter 7 to illustrate various aspects of computer simulation and optimisation and how they can help to identify optimal release conditions for the implement as the first step in technique optimisation. The necessity of adding complexity to an existing model should be revealed by continuously relating the results of the simulations to physical measurements.4. simulation can be defined as the carrying out of experiments under carefully controlled conditions on the real world system that has been modelled (Vaughan. 1995) would appear very reasonable indeed for the javelin (but see also Hubbard and Alaways. therefore. A simple rigid body or rigid rod model would be the next most simple and allows for the required rotation. In fact. The modelling process transforms the real system into a set of equations. has been to combine modelling and empirical studies. 1995). Thus.190 Biomechanical optimisation of techniques things being equal. which has been widely reported for some simulation models of airborne activities. 1984). to model a high jumper or a javelin as a point (the centre of mass) would be simple but would not capture the crucially important rotation of the jumper around the bar or the pitching characteristics of the javelin. This tests the model to see if it is an adequate approximation and what new features might need to be added. 6. In many computer simulations. termed simulation evaluation (e. This aspect of the process.2). The difficulty of interpreting the results.
Hardware costs have declined while hardware performance has improved. from Yeadon et al. . it is cheaper. such as SIMM. with permission).4. as many different simulations can be performed in minutes the potential for predicting optimal performance (section 6. Figure 6. 1990). such as AUTO LEV and MACSYM. Vaughan (1984) summarised the advantages of computer simulation as being: • • • • safety. have been developed. computer languages have improved. we will return to the latter issue in Chapter 8. and software packages for the simulation of human movement. At the same time.g. have become available. automated equation generating programs. Improvements in computer graphics offer sometimes spectacular ways of displaying information.2) cost. 1990.. The rapid growth of modelling and simulation of sport motions has been given a great impetus by the improvements in computer technology in the past two decades. Figure 6.. This approach could be adopted in many more cases and would help both in relating the model to the real world and in communicating the simulation results to coaches and athletes. to run a simulation than to build a prototype javelin. for example. as the athlete does not have to perform potentially hazardous experiments time saving.8 Simulation evaluation through comparison of a film recording of a twisting somersault (top) with a computer simulation of the same movement (bottom) (reproduced from Yeadon et al.8.Mathematical modelling 191 that the model results can be compared directly with the movements they model (e.
6. . range of the initial conditions. for a given jumper at a given stage of development. This type of optimisation is known as forward optimisation. simulation evaluation. There are many unresolved issues in simulation modelling. the middle one is self evident. However. what muscle models are needed for sport-specific models. the process of optimisation is expressed as the method for finding the optimum value (maximum or minimum) of a function f(x1. but realistic.192 Biomechanical optimisation of techniques He summarised the limitations as being: • • • the problem of model validation (or evaluation) the requirement for an advanced knowledge of mathematics and computers that the results are often difficult to communicate to the coach and athlete (feedback). Because of this. In Hubbard and Trinkle’s (1992) high jump model.2 OPTIMISATION Formally. in the high jump study reported by Hubbard and Trinkle (1992). and the adequacy of the rigid body model of human body segments (Bartlett. in contrast to the inverse optimisation that we considered in Chapter 4. 1984). sensitivity analysis. 1997a). A need exists. this can be considered as an operation on the mathematical model (the equations of motion) to give the best possible motion. The problem of model validation remains by far the most serious limitation.x2. the whole spectrum of possibilities for partitioning the take-off kinetic energy could have been used. as increasing the total kinetic energy at take-off is another way of increasing the height cleared (if the partitioning of kinetic energy is kept optimal). For example. The first and last of the limitations will be considered in the next two chapters. Optimisation can be carried out by running many simulations covering a wide. These include model complexity. neither of the last two is as great a limitation now as it was in 1984 when Vaughan wrote his review. for example the longest jump. Computer simulation clearly offers an inexpensive and harmless way of addressing the ‘what if?’ questions about how systematic changes affect important variables in sports techniques. therefore.4.…xn) of n real variables. Biomechanically. subject to the limitations of the model. to constrain the solution. optimisation normally seeks the minimum value of the function to be optimised (Bunday. the advice to increase the take-off kinetic energy will probably flout physiological reality. This example raises another important issue. This is a computationally inefficient way to search for the optimal solution to the problem and is rarely used today. Finding the maximum for the function f is identical to finding the minimum for -f.
As Best et al. By comparing the actual jump and the optimal jump for the given take-off conditions. it may also be necessary to consider the rules of the event (Hatze. (1995) pointed out.Mathematical modelling 193 two constraints applied: the total initial kinetic energy was constant and the high jumper had to just brush the bar. however. the choice of the performance criterion that is being optimised. It is possible to incorporate these rules as constraints on the optimisation although. Winters. In most running and swimming events this is time minimisation. relates to the possible existence of local and global optima (Figure 6. they will not be explored in any more detail in this book. not be possible. different starting points may give different answers for the local optimum while still missing the global one. However. It is possible that the points for judging aesthetic form could be included as constraints on permitted body configurations in a ski jump model. as in the example of Best et al. If. for example take-off vertical. long jump and downhill skiing. it was found that the gold medallist at the 1988 Calgary Winter Olympics could have obtained an 8% greater jump distance by changing his body configurations during flight. For example. which the jumper should use during flight to manipulate the body configurations to maximise the distance jumped. This simulation would not necessarily have improved the jumper’s overall performance. which can be optimised. 1983). Static optimisation (used for the high jump study) computes the optimum values of a finite set of quantities of interest. which will be considered in the next chapter. Optimisation performed in this way is referred to as constrained optimisation. no constraints are imposed on the dependent variable or on the independent variables in the model. a simple performance criterion exists. (1995). as in the ski jump of Hubbard et al. in the javelin throw for example. this may not be necessary as will be seen in Chapter 7. Furthermore. This may . tennis and hockey. These terms occur regularly in scientific papers on computer simulation and they affect the mathematical technique used. legs (assumed straight) and arms.9). javelin throw. Dynamic optimisation (also known as optimal control theory). horizontal and rotational kinetic energies. ice-skating.8 but not arrive at B. indeed. then the optimisation is unconstrained. seeks to compute optimum input functions of time. This was a planar model with four rigid bodies—skis. such as a small set of input parameters. This raises an important issue in optimisation.g. A further problem. we may find A rather than C in Figure 6. We also distinguish between static and dynamic optimisation (e. (1989). torso. to which we will return in Chapter 7. the optimisation process may return a local optimum and there is no known mathematical procedure that will bypass local optima and find the global optimum. on the other hand. which presents no problem. as the assessment of a ski jump involves not only the distance jumped but also a style mark. Constrained dynamic optimisation involved the computation of the best torques. In sports such as gymnastics. as functions of time. 1995). the specification of a performance criterion is more complicated and may. In the shot-put.
a range of different techniques is possible. Milsum (1971) addressed the evolutionary aspects of the problem and how the use of minimal energy confers an advantage both within and between species. for example the way in which spinal reflexes are ‘learnt’ as a balance between the energy needed for muscular effort and an error function. Figure 6. if speed itself is also important. related perhaps to anthropometric factors. the new optimisation criterion produces a new optimal speed. For example.9 Global optimum (minimum) at C and two local optima at A and B. He also demonstrated the existence of different optimum values of the independent variable for different optimisation criteria. In many sports. This selection could be based on some fundamental principle of human movement (Chapter 5). Explosive sports events will not have a minimal energy criterion as their optimising principle. There is some evidence to support this hypothesis. It is tempting to speculate that the process of evolutionary adaptation has led to the selection of the global optimum from the set of local ones. for a particular sport. for a given athlete. It is not necessarily the case that this minimum energy principle is always valid. but it might still be involved in the selection of a global optimum from a set of local ones. Further evidence to support the minimal energy principle includes the existence of the stretchshortening cycle of muscular contraction and of two-joint muscles. it could be postulated that the optimisation process may be extremely complex. probably that of minimisation of metabolic energy consumption. . each of which has an associated local optimum.194 Biomechanical optimisation of techniques reflect the fact that.
At present. have not become routine.4. Many of these have been Figure 6.Mathematical modelling 195 requiring a ‘trade off’ between information processing capacity and muscle power. similar to the one that Huffman et al. despite speculation in the early 1990s that they would. it is possible that biomechanists will increasingly turn to dynamic optimisation to seek solutions to problems in sport. we will address only sports in which the optimisation criterion is easily identifiable. real-time simulations. for example the flight phases of high jump. ski jump. In Chapter 7. (1993) developed for the bob-sled. 6. Some forward dynamics models for sports in which the performer is in contact with the surroundings have been developed. trampolining and gymnastic events. such as the javelin and bob-sled. 1991). diving. to date. and activities where angular momentum is conserved. .10 Simple simulation model of a thrower (after Alexander. most of the sports models that have gained widespread acceptance have involved equipment. The prediction of Vaughan (1984) that simulation packages such as that of Hatze (1983) would become widely adopted has also proved incorrect. However.3 CONCLUSIONS—FUTURE TRENDS As computer hardware prices continue to fall while their speed and memory size increase by similar amounts.
However.10) models of Alexander (1989. which has a simple performance criterion.5 Summary In this chapter.196 Biomechanical optimisation of techniques reasonably simple models. These include the jumper and thrower (Figure 6. simulation evaluation and optimisation were also provided.6 Exercises 1. 6. the computational requirements (computer time. multi-muscle movements such as walking (e. 1981. The differences between static and dynamic optimisation and global and local optima were covered. with an emphasis on theory-driven statistical modelling and computer simulation modelling and optimisation. Pandy and Zajac. The cross-sectional. 1988) and jumping (Hatze. Briefly outline the drawbacks to the trial and error approach to technique improvement. brief explanations of modelling. The relationships that can exist between a performance criterion and various performance parameters were explained and the defects of the trial and error approach to technique improvement were covered. The advantages and limitations of computer simulation modelling. were covered. How far do: (a) statistical modelling and (b) simulation modelling overcome these? 2. and the thrower models of Marónski (1991) which are discussed in more detail in the next chapter. simulation. that have allowed insight into the activity studied. 6.g. optimisation and practical improvement of sports techniques. models of the more complex sports movements are routinely used for the simulation. we considered the fundamentals underlying the biomechanical optimisation of sports techniques. Pandy and Berme. 1991). when seeking to evaluate and improve sports techniques. 1990. briefly list the most important assumptions of the following statistical techniques. memory and speed) of these optimisations are extremely large for complex three-dimensional sports movements. After reading the relevant sections of Mullineaux and Bartlett (1997). longitudinal and contrast approaches to statistical modelling were described and the limitations of statistical modelling in sports biomechanics were evaluated. It still remains to be seen how long it will be before reasonably accurate. The principles and process of hierarchical modelling were considered and illustrated using a hierarchical model of vertical jumping. The chapter concluded with a brief consideration of future trends in simulation modelling and the forward optimisation of sports movements. These models were not sufficiently complex to analyse the techniques of individual athletes. commonly used in statistical modelling in biomechanics: a) ANOVA b) linear regression . 1991) have been performed. yet not unnecessarily complicated. Dynamic optimisations of multi-segmental.
Which of these would you consider potentially the most important in analysing and improving the technique of a sports performer. longitudinal and contrast research designs. for example using the principles of coordinated movement in Chapter 5. 6.Exercises 197 c) multiple linear regression. Run an on-line or library-based literature search (e. simulation and optimisation. Choose a sporting activity with which you are familiar and which. respectively? What difficulties might you face in satisfying the assumptions of these statistical techniques in a field-based study of a specific sports technique? 4. List the advantages and limitations of computer simulation that were proposed by Vaughan (1984). c) Where possible. Obtain one of the research papers on mathematical modelling listed in the next section. In the hierarchical technique model of Figure 6. establish biomechanical justifications. How relevant do you consider each of these to be for the computer simulation of sports movements at the end of the second millennium AD? 8. Your model should be no more involved than that of Figure 6.2: a) Identify the primary performance parameters. You will need to give much more thought to the key words that you use in your searches than in the previous example.2. between each level and sublevel of the model.a) Choose a sports activity in which you are interested. 9. (Please do not refer to Chapter 8 when attempting this exercise. has a simple performance criterion. Medline) to identify the ratio of the number of references that cover computer simulation modelling of that activity to its total number of references. Imagine that you have a computer simulation model of javelin flight which allows you to predict the best release conditions (release parameter values) to maximise the distance thrown for a given thrower.) 10. You should seek to repeat the steps of exercise 4 during the development of your model. critically evaluate the model proposed and discuss any attempts made in the paper to perform a simulation evaluation. Distinguish between modelling. Suggest two ways in which you might seek to evaluate the accuracy of your simulation model. b) Repeat for the same sports activity but for statistical modelling rather than computer simulation modelling. Prepare a summary of the findings of the paper. 3. Which of the above statistical techniques would be appropriate for crosssectional.g Sports Discus. 5. preferably. and why? 7. . Are you surprised at the result? Try to explain why the ratio is so small (or large) in relation to what you might have perceived to be the value of computer simulation of sport movements. b) Identify wherever the step of subdivision of the performance criteria has been used. Develop a hierarchical technique model for this activity.
J. J.G. (1990) Optimum take-off techniques for high and long jumps. Alexander. (1995) Optimal javelin release. 14. J.G. England. Journal of Sports Sciences. (1981) A comprehensive model for human motion simulation and its application to the take-off phase of the long jump. Bartlett. Mechanics and Human Motion. Bartlett. MD. 58–71. and Dapena. (1986) The techniques of elite male long jumpers. p. 19. 14.. (1976) Kinematic and dynamic characteristics of the sprint start. Englewood Cliffs. 349–372. et al. 1. in Biomechanics V-B (ed. Hatze.D. J. 3–12. H. Bartlett.Komi).. D.. Hatze. Series B. NJ.M. 13–19. Bartlett. USA. (1984) The pattern of hammer speed fluctuation during a hammer throw and influence of gravity on its fluctuations. S.M.A. Hay. University Park Press. pp. P. and Cunningham.Schneider). R. Martinus Nijhoff. S. Baltimore. Proceedings of the Royal Society of London. Journal of Biomechanics. (1997a) Current issues in the mechanics of athletic activities: a position paper.D. R. 371–394.G. 3–10.G. 1–2. 855–866.McN. K. Hay. (1991) Optimal timing of muscle activation for simple models of throwing. R. 16. Müller. (1988) Anatomy. H. Journal of Applied Biomechanics. (1976) Identification of the limiting factors in the performance of a basic human movement. Journal of Applied Biomechanics.. Journal of Biomechanics. Human Movement Science. pp. Hay. and Reid. 553–559.McN. Dapena. 339–345. (1989) Sequential joint extension in jumping. (1984) The standing vertical jump. in Biomechanics V-B (ed. Best. London.McN.G. Dordrecht. R. Journal of Biomechanics.Perren and E. 30. R. 49–60. R. Bunday. Bartlett.V. England. 329. Hay. A. (1984) BASIC Optimisation Methods. 135–142. 422–425. (1996) Three-dimensional evaluation of the kinematic release parameters for javelin throwers of different skill levels. PrenticeHall.A. USA. Netherlands.198 Biomechanical optimisation of techniques Alexander. B. R. 194–199. R. Edward Arnold. 6. J. R. and Parry. (1984) Regression analysis in physiological research: some comments on the problem of repeated measurements. J. 477–486. 17. MD. (1985) Issues in sports biomechanics. E.M. 11.W. B. 8. Komi).M.7 References . and Canterna. 150. R.A. Lindinger. Journal of Sports Sciences. J.V.M. a measure of power? Communication to the Sport and Science Conference. J. Donner. 12. Miller. and Sawyer. Baumann. Journal of Theoretical Biology. P. in Biomechanics: Current Interdisciplinary Perspectives (eds. Bedford. W.. Medicine and Science in Sports and Exercise. (1983) Computerised optimisation of sports motions: an overview of possibilities. Baltimore. University Park Press. Journal of Biomechanics. R. methods and recent developments. Wilson. USA. Alexander. (1997b) The use and abuse of statistics in sport and exercise sciences.J.M.
M. in Proceedings of the Sports Biomechanics Study Group. International Journal of Sport Biomechanics. Karger. H. Journal of Biomechanics. Leeds.. 1–10. 207–221.J. Human Kinetics. (1992) Statistical Methods for Psychology. 1. 139–150. 3. and Alaways. IL. University Park Press.Wit). P. Howell. R. A.M. Komi. in Biomechanical Analysis of Movement in Sport and Exercise (ed. D. 24. M. pp.M. M. J. E. and Mero.E. Zurich. (1989) A multisegment dynamic model of ski jumping. J. 21.G. W. 81–104. I. Hubbard.R. 1043–1051. (1995) Statistics in Kinesiology. Journal of Sports Sciences. (1984) Computer simulation of human motion in sports biomechanics. 62–71. MD. Hubbard. in Biomechanics II (eds J. Milsum. (1995) Concepts of neuromuscular modelling. R. Neukomm. and Zajac. (1991) Optimal distance from the implement to the axis of rotation in hammer and discus throws. A.Stokes and J. (1991) Optimal muscular coordination strategies for jumping. K.V. Baltimore. J. Champaign. Macmillan. Raschner.Bartlett). in Exercise and Sport Sciences Reviews—Volume 12 (ed. 9. (1987) Optimal release conditions for the new rules javelin. 258–274. 24. J.M. Vol. Journal of Applied Mechanics. C. USA. B. Marónski. D.. N. USA. R. in Advances in Bioengineering. Hibbard. Vaughan. in Three-Dimensional Analysis of Human Movement (eds P. Pandy. 263–266. (1971) Control systems aspects of muscular coordination.K. R.A. Journal of Biomechanics. and Waser. 373–416.. Journal of Biomechanics.L. et al. 179–184. Champaign. 545–559. and Trinkle. ETH.. Hubbard. New York. M. (1980) Leistungsbestimmende Faktoren im Zehnkampf. and Komor. (1988) A numerical method for simulating the dynamics of human walking. England. R. International Journal of Sport Biomechanics. (1993) Use of an interactive bobsled simulator in driver training.R. 265–271.Allard. Leistungssport. 5. and Reus. Summer. L. Hubbard. M. C. Yeadon.-R.W. International Journal of Sport Biomechanics.-P.Blanchi). (1981) Technique and performance: identifying the limiting factors. American Society of Mechanical Engineers. Pandy.F. Bartlett.M.Wartenweiler). J.C. Vincent. Human Kinetics. 511–520. CA. and Berme. and Bartlett. F.. (1997) Research methods and statistics.L. British Association of Sport and Exercise Sciences. USA. Nigg.References 199 Hay. Winters. M. IL.H. 999–1005. M. (1998) Comparisons of the ski turn techniques of experienced and intermediate skiers. 52... Parry. R. Kunz. USA. and Woodworth. J. 16. (1985) Biomechanical analysis of olympic javelin throwers.Terjung). R.L. Müller.G.G. . (1984) Biomechanical optimisation of performance in the long jump. and Bartlett. pp. Mullineaux. Fidelus and A. R. New York. P. Basel. Vaughan. C.C. pp. (1973) Messungen im Weitsprung an Weltklassespringen. pp.M. Switzerland.Vredenbregt and J. pp. G. in Biomechanics VII-B (eds A.G. Belmont. K.Morecki. Switzerland. Duxbury Press.L. (1992) Clearing maximum height with constrained kinetic energy.A. Huffman. 26.
D.Bartlett). in Exercise and Sport Sciences Reviews—Volume 12 (ed. 23. Vaughan. 373–416.D. pp.M. (1984) Computer simulation of human motion in sports biomechanics. . F. J. NJ. Englewood Cliffs. British Association of Sport and Exercise Sciences. 6. New York. J. England.8 Further reading Hay. Atha. M. (1990) The simulation of aerial movement. Mullineaux. USA. R. (1997) Research methods and statistics.G.G. J. (1988) Anatomy. R.Terjung). Chapters 15 and 16. in Biomechanical Analysis of Movement in Sport and Exercise (ed.R.L. This provides a clear and non-mathematical treatment of many of the problems involved in statistical modelling in biomechanics. Macmillan.. 85–89. Mechanics and Human Motion. and Hales. These chapters provide excellent detail on the principles and process of hierarchical technique modelling and are strongly recommended. and Bartlett. this still remains one of the most readable and general (in its sports applications) accounts of the use of computer simulation models in sports biomechanics.R.M. Although now somewhat dated. 81–104. Leeds. pp. PrenticeHall. C. Part IV: a computer simulation model. R. Journal of Biomechanics.L.200 Biomechanical optimisation of techniques Yeadon. and Reid.
yet which is nonetheless very relevant to the optimisation of sports movements. After reading this chapter you should be able to: • understand the modelling. 1995). optimisation and simulation evaluation stages in several examples of computer simulations of sports movements • critically evaluate these four stages for the examples of optimal javelin release and optimisation of implement radius in the hammer and discus throws and for other examples from sport and exercise • undertake a critical evaluation of computer simulation of an aerial sports movement of your choice • interpret graphical representation of optimisation and use contour maps to identify likely ways to improve performance • outline ways in which simulation evaluation might be performed for specified simulation models • compare and contrast three models of human body segment inertia parameters • evaluate existing models of human skeletal muscle and their use in both general computer simulation models of the sports performer and establishing optimal sports techniques. we will illustrate this process by considering two examples of computer simulation and optimisation of sports techniques.1 Introduction . This will be done by close reference to published examples. In the first half of this chapter. This has been chosen as it involves a relatively simple modelling problem. which can be reasonably easily comprehended.Mathematical models of sports motions 7 This chapter will build on Chapter 6 and extend your understanding of the uses of computer simulation modelling in the biomechanical optimisation of sports techniques. The first of these involves establishing the optimal values of the release parameters for the javelin throw to maximise the distance thrown (Best et al. A less hazardous alternative to the trial and error approach when seeking to improve a sports technique is to use the dynamics of the event and optimisation.. simulation. Because 7.
this is referred to as an initial condition problem. The second example in this chapter involves the optimal solutions for hammer and discus throwing using rigid body models of the thrower (Marónski. in which optimal control theory might seek to establish the optimum time courses of the muscular torques of the thrower. the most interesting of the four throwing events.1). which are specific to a given thrower. In javelin throwing. and a performance criterion exists that is a function of the system variables and that is to be maximised or minimised (Swan. 1982). simulation. can be applied to any problem in which: the behaviour of the system can be expressed in terms of a set of differential equations. the flight path of which is beyond the control of the thrower. Finally. including the modelling of the skeletal system and the muscles that power it. The second of these is characterised by only gravitational and aerodynamic forces acting on the implement. 1984). Soong. the initial conditions needed to solve the equations of motion for the flight of the javelin include the translational and rotational . This is a static optimisation. more complex models of the sports performer will be covered. The javelin flight is. or dynamic optimisation. Optimal control theory. In the second part of the chapter. in which the implement is acted upon by the thrower. 1991). the optimisation problem is to find the optimal values of these to produce the maximum range (the performance criterion). This forms a relatively simple problem in comparison with the thrust stage. The flight phase of the throw is a classic initial condition problem in optimisation (Best et al. simulation evaluation and optimisation (Figure 6. As was seen in the previous chapter.202 Mathematical models of sports motions this example involves the optimisation of only a small set of instantaneous values of a set of variables. 1995). because the instantaneous values of these variables (the release parameters) determine the flight of the javelin.. a set of variables controls the behaviour of the system. the overall process of optimisation generally involves several stages—system modelling. The initial conditions for such an event are the set of release parameter values.2. In this case. This would apply. 1989). for example. it is a static optimisation. since only a finite set of instantaneous (parameter) values is involved. in most respects. These stages will be critically evaluated for each of the two models chosen. some optimisations of sports motions using complex body and muscle models will be considered. 7. although the flight of the discus is far more complex because of its three-dimensionality (see Frohlich. to the thrust phase of the javelin throw. 1981.1 THE JAVELIN FLIGHT MODEL Throwing events can be considered to consist of two distinct stages: the thrust and the flight (Hubbard.2 Optimal javelin release 7.
(b) translational. that is the moment tending to rotate the javelin about its short. the speed of the javelin’s mass centre.Optimal javelin release 203 position and velocity vectors. Jia. They noted in particular that the positions of the aerodynamic centre (centre of pressure) had resulted in a very wide range of functional variations of this parameter with angle of attack (e.1 Javelin release parameters: (a) rotational. The vibrational characteristics of the javelin at release are also important (Hubbard and Laporte. Additionally. 1997). and the angle of the javelin to the relative wind (the angle of attack) (Figure 1b). 1989). although these are beyond the control of the thrower. roll and yaw at release (Figure 7. They reported that they could find no consistency between investigators—all preceding simulation results had produced different predictions. the release height. horizontal axis (Figure 7. the model might need to incorporate the effects of wind speed and direction. Bartlett and Best.1). This would present a far from trivial wind tunnel experimental problem. They therefore decided to continue with the two-dimensional model. 1988. A three-dimensional model of javelin release and flight would require aerodynamic force and moment data from a spinning and vibrating javelin at various speeds and aerodynamic angles.1a). because that model had not yet given consistent enough results to justify proceeding Figure 7. the distance from the foul line. Best et al.g. These are the rates of pitch. (1995) therefore examined the literature on two-dimensional wind tunnel tests of the javelin. This position is calculated from measurements of pitching moments. . In addition to these initial conditions. the angle of the javelin’s velocity vector to the ground (the release angle). the model requires the specification of the javelin’s mass and principal moments of inertia and the aerodynamic forces and moments acting on the javelin in flight.
they noted that an optimal release for an elite thrower is hardly likely to involve javelin yaw and will probably minimise vibration. yawing and vibrating javelin within a region of the turbulent atmosphere in which the air speed varies considerably with height. There is little evidence in the literature to assess the interdependence or otherwise of . different techniques in this stage might affect the required distance to the foul line to avoid making a foul throw. and the lift and drag forces and pitching moments acting on the implement.204 Mathematical models of sports motions to a model of greater complexity. The distance to the foul line is not included as it does not affect flight and relates to the thrust stage. and the true aerodynamic characteristics of a spinning. These defects were primarily the use of single sample data and a failure to account for interactions (or crosstalk) between the force balances used to measure the component forces and moments. laminar flow wind tunnel tests on non-spinning javelins). Furthermore. The wind speed is not a release parameter and is beyond a thrower’s control. as most earlier studies have reported insufficient experimental information even to enable error sources to be identified. The equations of motion for this simplified. 7. they took great pains to avoid such errors in their results. Nevertheless. within realistic limits. pitching.2. and that defects in these measurements were a feature of many previous studies. as was pointed out by Bartlett and Best (1988). The range now depends solely upon: • • • • • • release speed—v(0) release height—z(0) release angle—γ(0) release angle of attack—a(0) release pitch rate—q(0) wind speed—Vw. and studying their effects. (1995) used a trifilar suspension method for establishing the moment of inertia. it is not known what the discrepancies are between these results (from two-dimensional. However. Best et al. This allows model simulation by varying the values of the release parameters. They noted that accurate specification of the aerodynamic forces and moments acting on the javelin was essential to simulate and optimise the flight successfully. the throw distance (the performance criterion) can be expressed in terms of the release parameters.2 SIMULATION From the above modelling considerations and the two-dimensional equations of motion. and they reported the methods for obtaining these data in considerable detail. Their identification of these as major errors was somewhat speculative. two-dimensional model include the moment of inertia of the javelin about its short (pitching) axis.
1) where the angles must be in degrees and the speed in m·s-1. Of the five remaining independent variables. equation 7.. Best et al. then an optimal set can be found at a global maximum where (with R as range): (7. an optimisable parameter.2.2. Surprisingly.2 is true for all local optima . 1988).2. the nominal release speed is non-variable as implied in subsection 7. expressed by the equation: release speed=nominal release speed (vN)—0. and release pitch rate (q(0))—are allowed to vary independently. 7. (1995) therefore discarded it from the set of parameters that they investigated. Two pairs of investigators have investigated this relationship. The nominal release speed is defined as the maximum at which a thrower is capable of throwing for a release angle of 35° and replaces release speed in the set of release parameters.13 (release angle—35) (7. and small changes beyond these limits detrimentally affect other. The numerical techniques used to perform the simulations are beyond the scope of this chapter (see Best et al.1995). one using a 1 kg ball (Red and Zogaib. after introducing the relationship of equation 7. The release height is.2) The solution involves. they obtained very similar relationships over the relevant range.3 OPTIMISATION An optimisation can now be performed. 7. (1995) carried out a sensitivity analysis—a detailed evaluation of the system’s behaviour to changes in the release parameters—using contour maps. This fulfils two roles.. in normal javelin throwing it varies only slightly for a given thrower. a mathematical procedure to find a peak on a hill of n-dimensions (where n is the number of dependent plus independent variables. If the remaining three parameters—release angle (γ(0)). at least conceptually. 1995).2. in principle. 1977) and the other using an instrumented javelin (Viitasalo and Korjus.1 and neglecting wind speed. release angle of attack (a(0)). The two for which there is a known interrelationship are release speed and angle.4 A SENSITIVITY ANALYSIS Best et al. The details of these mathematical procedures are beyond the scope of this chapter (see Best et al.Optimal javelin release 205 the five release parameters. more important parameters. Firstly. However. four in this case).
The only way to check on the number of peaks is to look at the full solution—a threedimensional surface: R=f(q(0).α(0). so that all optimisation techniques find a local optimum that may.γ(0)). 1995). was a detailed evaluation of the contour maps to establish. Figure 7.2. . This is important as it may relate to distinct identifiable throwing techniques. An example of a contour map for this problem is shown in Figure 7. The second aspect of sensitivity analysis. z(0)=1. for example. whether the optimum is a plateau or a sharp peak.2 Full contour map showing range (R) as a function of release angle and release angle of attack for N86 javelin. Vw=0 and q(0)=0.. Furthermore. helping to define positive directions for training regimes (Best et al.9). (1995). or may not. This is not usually possible as only two independent variables can be viewed at one time using contour maps (see next section) while the remaining independent variables have to be kept constant. This is not possible using optimisation alone. different local optima may be found from different starting points (as in Figure 6.206 Mathematical models of sports motions as well as the global optimum. remaining release parameters constant at: VN=30 m·s-1.8 m. This provides enormous insight into the best way to reach the peak. be global. as defined by Best et al.
This solution was verified by zooming in on the global peak. for a small (less than 3 m·s-1) range of nominal release speeds (Figure 7.3). i. For all javelins this showed a double peak to exist. (1995) reported that different optimal release conditions were found for throwers with differing nominal release speeds and for different Figure 7. Vw=0 and q(0)=0.4). z(0)=1. .3 Contour map highlighting dual peak phenomenon for range (R) as a function of release angle and release angle of attack for N86 javelin. optimum.8m. Best et al. The reality of the peaks. remaining release parameters constant at: VN=30m·s-1. This shows a discontinuity where one peak ‘overtook’ the other (Best et al. 1995). that they were not an artefact of the contour plotting algorithm.e. The peaks were so close together that the optimisation algorithm usually ‘jumped over’ the local optimum along the ridge approaching the global peak. except where the starting position for the search was at the other. such as those reported by Hubbard and Alaways (1987). local.Optimal javelin release 207 where only one optimum is apparent.. was verified by a plot of optimal release angle of attack as a function of nominal release speed (Figure 7.
α(0)=22°. throwers with different nominal release speeds can. as the nominal release speed increased from 26 m·s-1. A85—Apollo Gold Old (pre-1986) Rules. Because of the plateau near the optimal solution. for a release height of 1. γ(0)=30°. α(0)=-7°. javelins. α(0)=6°. vN=30 m·s-1. the shape of the hill was simple and tended to a plateau as the solution to equation 7. A86—Apollo Gold New Rules. They also noted that a wide range of non-optimal release conditions can produce the same range. the Nemeth javelin would travel 86 m for any of the following angle combinations: α(0)=20°. α(0)=10°. the range will be very sensitive to at least one of the release parameters. q(0)=0. in some circumstances. a thrower with near optimal values finds that the range is insensitive to small changes in release parameter values.2 and 7.8 m. and two women’s javelins: A90— Old (pre-1991) Rules Apollo Laser. for whom changes in both angles have relatively large effects on the range. Also. . γ(0)=42°. As Figures 7. γ(0)=40°. nominal release speed of 30 m·s-1 and zero pitch rate.05 rad·s-1. however. They pointed out that confusion could arise for a thrower with an optimal release angle of attack but a non-optimal release angle. only a study of the contour map could reveal that it was the release angle that was non-optimal.2 was reached. would both result in the Nemeth javelin travelling 82 m. in still air.208 Mathematical models of sports motions Figure 7. For this thrower. the optimal release angle and optimal release angle of attack increased and optimal pitch rate decreased. (1995) also noted that the shape of the hill provided a great insight into the complexity of coaching. γ(0)=24°. Away from the optimum. α(0)=-6°. γ(0)=30°.3 demonstrate. Best et al. For a given thrower and javelin. q(0)=0. γ(0)=32°. throw the same distance. A91—New Rules Apollo Gold.4 Optimal release angle of attack as a function of nominal release speed for three men’s javelins: N86—Nemeth New Rules (now illegal). For example. The following release parameter sets: vN=28 m·s-1.
(1995) because their simulations had produced different optimal release conditions from those of previous studies (see. This confirmed some important assumptions underlying the two-dimensional model of an optimal release. perhaps necessarily. specified to be capable of repeated throws with the same release conditions and able to control all relevant release parameters (speed. spin. In practice. with an average discrepancy modulus of only 1. as might be expected for model errors. (1995) because of their use of aerodynamic data from non-spinning. of the three stages of optimisation because of assumptions that have been made. (1995) considered their findings to show that the trial and error approach discussed in the previous chapter was unrealistic. An evaluation of the appropriateness of the two-dimensional model of javelin release was carried out using the best throws at the 1991 World Student Games (Best et al. was sought by Best et al. and it was small. in many cases. the sheer complexity of such an evaluation may make it. (1995) considered that only sensitivity analysis can define positive. The discrepancy was not systematic. Simulation evaluation was considered especially relevant to the study of Best et al. It would also not be known if the performer was physically capable of altering the technique.4 m (for throws over 81 m).5 SIMULATION EVALUATION Best et al.g. Furthermore. Best et al. angle of attack and pitch rate) and with vibrations being naturally induced by certain release conditions. relevant directions to improving performance. 1988. Those authors pointed out that errors or uncertainties may be introduced in any one. 1993). They recommended that simulation evaluation should always be at least considered. using a javelin gun. 1989). non-vibrating javelins. They proposed the construction of a javelin gun. Jia. unfeasible. Such an approach seeks to change a technique without knowing the performer’s current ‘position’ in the overall ‘solution’—for example.. The release parameters from the World Student Games study were also used to calculate the theoretical flight distance for three throws using javelins for which the authors had measured the inertia and aerodynamic characteristics. angle.Optimal javelin release 209 7. Bartlett and Best.2. These distances were then compared with the measured throw distances. This provided limited evidence of the accuracy of this simulation model. or more. This showed that those angles that would indicate a departure of the javelin release from the two-dimensional model had values close to zero for all throws. height. e. little is known about the interactions between independent variables and any physical or injury constraints that may be relevant. the construction of . where the thrower’s release conditions are located on the contour maps. arguing that the results of such a study should provide an accurate representation of the real world. However. An alternative approach to simulation evaluation.
1 INTRODUCTION In the previous section. Of the three standard models of the sports performer (see Bartlett. In the final. throughout the throw phases after entry into the turn. In Chapter 6. 7. some competitors reduce the radius of the hammer (Marónski.3. 1991). the hammer head speed (v) is further increased by maintaining or increasing the radius of the hammer from the axis of rotation (r) while increasing its rotational speed about this axis ( ) [v=r ]. The specific technique element addressed by Marónski (1991) was to find the optimal hammer or discus position with respect to the axis of rotation to maximise the release speed of the implement. the hammer is accelerated to about one-half of its release speed before entry into the turns (Morriss and Bartlett. delivery phase. In this section. This section will have as its focus the use of a similar. 1991). Rotation occurs in all sports techniques. quasi-rigid body model to investigate some specific optimum motions in the thrust stage of the hammer and discus throws (Marónski. During this period. 1991). preceding release. is kept large. where the radius of the implement from the axis of rotation. This shortening of the implement radius is not seen in the discus throw. we will address the more complex problem of modelling. which had important repercussions for the thrower in seeking to achieve the optimum release conditions. whose feet remain in approximately the same position at the rear of the circle. During this period. mainly because of health and safety issues. simulating and optimising the movements of the sports performer. 1982) was briefly considered.210 Mathematical models of sports motions this device proved to be both technically and economically unfeasible. A second element contained within this was to ascertain whether any benefit resulted from the shortening of the radius in the hammer throw. the point (centre of mass) model has been seen in the previous chapter to be inadequate as a representation for any movement that involves rotation. . 1997). The hammer thrower performs a series of preliminary swings or winds in which the hammer is turned around the thrower. the use of the rigid body model in optimising the movements of a high jumper (Hubbard and Trinkle. and whether a similar benefit might accrue from the use of a similar technique in the discus throw. optimisation theory was applied to a problem involving the motion of a sports implement. The three or four turns then involve the thrower and hammer rotating about a common axis while the thrower moves in an almost straight line across the circle.3 Simple models of the sports performer 7.
the magnitude of this variable and the fluctuations in it are small compared with the term mr2 for the hammer. • The thrower rotates about an axis which is vertical (Figure 7. in relation to the axis of rotation.Simple models of the sports performer 211 7. It also ignores the rotations of the thrower’s hips and shoulders with respect to each other and to the implement. The relevance of this comment to the discus throw was not mentioned by Marónski (1991). The solution for r was constrained within the maximum and minimum limits dictated by the thrower’s physical characteristics.5) and that the plane in which the implement moves is horizontal. although the thrower does not behave as a rigid body and thus the value of I is not constant. when the implement and thrower rotate together. Marónski (1991) argued that. it is not constant as the hammer throw involves single and double support phases and the discus throw also has a short airborne phase.5).3. This is a problem of dynamic optimisation. 1991. • • • • • The modelling problem was then formulated by Marónski (1991) as being to find a continuous function r( ) that will maximise the tangential velocity component (v) of the implement at the moment of release. or moment (M). which is constant. therefore. The transverse component alone was chosen as the performance criterion. . Morriss and Bartlett. can be represented by a radius (r) which is a function of the rotation angle ( ) of the thrower-implement system. not a parameter that can be optimised. 1991). 1991). The thrower is a quasi-rigid body having a constant and known moment of inertia (I).2 THE THROWER MODEL The main assumptions in the model were as follows (Marónski. The implement can be treated as a point mass (m) whose position. This ignores the fact that the implement (particularly the hammer) moves in a plane with a gradually changing angle to the horizontal. As Marónski (1991) noted. this ignores the forward movement of the thrower across the circle to add his or her speed to that of the hammer. This torque is to be understood as an average value for the throw. The angular coordinates ( ) of the thrower’s body and the implement are the same (Figure 7. The thrower is powered by a torque. ff) are known. allowing f to be regarded as the independent variable. He failed to point out that the same statement is far from true for the much lighter discus. at the feet about the vertical axis. no other limits within that range were imposed on the initial and final values of the implement radius. which are notable features of both throwing techniques (Lindsay. because the other component—the time rate of change of r—is unlimited and. Only the turns of the hammer throw are considered. The initial and final rotation angles (fi.
1 is the initial rotation angle and vthe hammer velocity (after Marónski. the implement mass (m).f). The values for m are well known. and the initial minus the final rotation angle ( i. m the point mass of the hammer head. 1991). Marónski (1991) provided no details of the sources from which the values of the other parameters were obtained.212 Mathematical models of sports motions Figure 7. but the release value followed from the solution of the problem. the ground contact torque (M). The angular velocity of the implement at entry to the turns was fixed by the preliminary movements. The solution required given values of the thrower’s moment of inertia (I). however. which is an unknown function of the rotation angle ( ) of the thrower-implement system. r( ) is the hammer head distance from the axis of rotation. . r is within the maximum (rmax) and minimum (rmin) limits dictated by the thrower’s physical characteristics.5 The hammer thrower: (a) side and (b) plan views of the model with: M the constant moment derived from the thrower’s feet.
For these ‘optimal control’ subarcs. These are the contour lines of the performance criterion. the dashed lines are hyperbolas of R=constant (where = 2). the angular impulse-momentum equation: the integral of the torque acting equals the change of angular momentum. To facilitate understanding of this important solution. As in section 7. the nature of the assumptions. he proposed a suboptimal solution for the hammer throw. either the implement radius (and R=r2) was a constant or the angular momentum (K= r) and. their use as the axes of Figures 7.6 and 7. remained constant during a rapid displacement of the implement.6b. R.6a. the analogy can be drawn of ascending a mountain. The optimal throw is constrained to the zone between Rmin and Rmax. the constraints of the minimum and maximum hammer radius (or Rmin and Rmax) have been added as shaded vertical bars.6 and 7. The manipulation of this into an equation and suitable control functions for use of the methods of optimal control theory was detailed by Marónski (1991).7). particularly for the discus throw. . The angular velocity of the hammer at the start of the turns ( 1) is also shown as a horizontal line. from a constant radius by rapid displacement of the implement. OPTIMISATION AND SENSITIVITY ANALYSIS The basic equation for this problem is simply Newton’s second law for rotational motion. suggests a requirement for simulation evaluation. but required the use of R (=r2) and (= 2) as the variables in the control equations (hence.6. at the end of the turns.6d. this figure has been built up in four stages. The latter solution followed from consideration of the angular impulse-momentum equation. Further details of the simulation and optimisation are beyond the scope of this chapter. Consideration of the optimal control equations showed the optimal solution to consist of a series of subarcs (Figures 7. The performance criterion in Figures 7.2. In Figure 7. However.6 and 7. 7. In this. striving to reach the greatest value of the performance criterion—as represented by the arrow in Figure 7. which the thrower should try to maximise.3 SIMULATION. only one switch was made. The optimal solution involved maximising the tangential release speed of the hammer under certain constraints. The solution for the hammer throw is represented by Figure 7.Simple models of the sports performer 213 You should seek to evaluate the above set of assumptions further (see exercise 5). In Figure 7. As Marónski (1991) could provide no evidence to establish any patterns of ‘switching’ between these optimal controls.7 is the square of this tangential speed. The model sufficiently fulfils the ‘keep it simple’ requirement.3.7). hence.
Note that the axes are = 2 and R=r2. cannot pass beyond this line of limiting 2 (= ). cC. .6b Figure 7.6a Figure 7. along with the square of the angular velocity at entry to the turns ( 1). Lines of constant R.6 The suboptimal solution for the hammer throw. of which three are shown.214 Mathematical models of sports motions Figure 7. (b) The maximum and minimum hammer radius constraints have been added to (a). bB. (c) The curved dotted line ABC denotes the square of the angular velocity of the thrower-implement system ( 2= ) obtained from integration of the equation of motion for different constant values of R. aA. (a) The hyperbolas R= 2r2=constant (dashed lines) are the counter lines of the performance criterion. the thrower should seek to maximise this (to maximise the tangential velocity of the hammer).
6d (d) The curved solid lines with arrows. 1991). maximal radius (from c to C) and a rapid shortening (from C to F) just before release (after Marónski.6c Figure 7.5 decreases so that = 0. They show how the performance criterion ( R) can vary as the radius changes with constant angular momentum: note that moving to the left along one of these arcs. r=R0. The attainment of point F along the curve CF is possible by a rapid decrease of the radius of the implement from the axis of rotation just before release: at point F the performance criterion (dashed lines) has a greater value than at point C. Therefore.5 must increase. . are lines of constant angular momentum. the suboptimal solution consists of rotation with a constant. such as CF.Simple models of the sports performer 215 Figure 7.
An increasing radius strategy would move from B to E. representing the solution that the hammer radius is a constant (R=constant). aA or bB. constant values of the hammer radius. For discus throwing (Figure 7. Use of an arbitrary constant radius (R=0.5 decreases so that = 0. An optimal solution for these constant radius subarcs should be immediately apparent from Figure 7. where the performance criterion is still much less than at F. Thus cCF is the suboptimal (single switch) throwing strategy.4m2) from B’ until just before release resulted in the achievement of the limiting angular momentum at B. These subarcs show how the performance criterion ( R) can vary as the radius changes with constant angular momentum: note that moving to the left along one of these arcs. The ‘optimal’ solution constant radius strategy that we identified from Figure 7. decreased (to D) or increased (to E) while . bB and cC. the radius of the hammer should be kept at its maximum value to follow the subarc cC—the value of R will increase throughout the turns because of the ground reaction torque.6c.6d has three more subarcs added. constant radius strategy is represented by bB. The suboptimal solution proposed by Marónski (1991) should be evident from this figure.g. An increasing radius strategy would move towards D. This change is possible by a rapid decrease of the radius of the implement to its lowest possible value (Rmin) in the delivery phase just before release. maximal radius (from c to C) and a rapid shortening (from C to F) just before release. these are the vertical lines with arrowheads aA.6c can be improved upon. Therefore. This change of radius should be made only after full effect has been taken of the ground reaction torque to increase while R remains constant. This exceeds the performance criterion that can be achieved with any alternative constant radius strategy (e. the performance criterion would decrease. For a given torque impulse. these are the curved solid lines with arrows which are the optimal solutions for constant angular momentum.7). the suboptimal solution consists in rotation with a constant. reducing the performance criterion. r=R0. one set of three subarcs has been shown. This represents the square of the angular velocity of the thrower-hammer system obtained from integration of the equation of motion for different. the limiting value of R for the latter is only 400 m2·s2). It should be noted that point F cannot be reached in any other way. the radius of the hammer could then be increased or decreased.216 Mathematical models of sports motions In Figure 7. Using this throwing strategy. if the radius was then increased along a constant momentum subarc. This can be done by following the constant angular momentum subarc CF to the limiting radius point F: at point F the performance criterion (dashed lines) has a greater value (over 800 m2·s2) than at point C.6c. From B. That is. The radius could now be maintained. an R value of well over 500m2·s2 can be achieved at release. A minimal radius strategy throughout would reach only point A (from a along subarc aA). Figure 7. a different conclusion was reached. Also added to this figure is the dotted line ABC. An intermediate. the subarcs of constant R cannot pass beyond this limiting line.5 must increase.
a greater value of the performance criterion could be achieved at point at C. The optimisation performed here identified suboptimal strategies for the two events. Marónski (1991) noted that this has further benefits. maximal distance to the axis of rotation (from C’ to C). the suboptimal solution consists of rotation with a constant. 1991). However. for example) resulted in a deterioration in the performance criterion to below 200m2·s2 at F. therefore. He did not. maintaining constant angular momentum. as the lower angular velocities allow the leg muscles of the thrower to exert stronger forces and permit a greater driving moment from the ground. The symbols are similar to those in Figure 7. Both events. however. but the solution is different. The last of these resulted in the greatest value of the performance criterion (about 350 m2·s2) for this value of angular momentum (K). a path of constant. have a suboptimal strategy that involves keeping the implement at a large radius from the axis of rotation at least until the delivery phase. Thus C’C was the best throwing strategy for the discus. but this required the thrower to follow path C’C. this causes a decrease in the performance criterion (dashed lines).7 The suboptimal solution for the discus throw. Shortening of this distance is not an optimal strategy in the discus throw (after Marónski. incorporate this into his models.Simple models of the sports performer 217 Figure 7. No increased radius option was then open and the decreased radius option (to F. maximum radius. The attainment of point F along the curve CF is possible by a rapid decrease of the distance of the implement from the axis of rotation just before release: however. Whether these are also .6. Therefore.
because the ratio of the implement mass to the thrower’s mass is small. The former author had. 1991). had not specified his assumptions and had not applied the methods of optimal control.8 Another model of the thrower-hammer system. there was no fundamental change to the results. .3. remote component into the equation for the thrower’s moment of inertia equal to . This required changes to the parameters in the model above but. not considered the possibility of increasing the implement’s speed by shortening its radius. A second vertical axis passes through the centre of mass of the thrower. shoulder axis and throwing arm in the discus throw made the model Figure 7.8). where rt=m r/mt (m being the implement mass and mt the mass of the thrower). performed. 7. rt( ) is the distance between the two vertical axes (after Marónski. only minor changes to the values obtained. Townend (1984) considered the possibility of radius reduction for the hammer but not for the discus throw. This introduced a second.218 Mathematical models of sports motions optimal strategies cannot be established in the absence of evidence about how many switchings between the set of optimal subarcs should be. This model assumes that the vertical axis of rotation passes through the centre of mass of the thrower-hammer system. Marónski (1991) also commented that the sequential actions of the hip axis. Marónski (1991) also considered a second variant of his model in which the (vertical) axis of rotation of the thrower–implement system passed not through the centre of mass of the thrower but through the common centre of mass (Figure 7.4 SIMULATION EVALUATION As Marónski pointed out. however. and can be. some previous consideration of this problem had been made by both Tutjowitsch (1969) and Townend (1984).
possibly. the angular displacement of subsystem 1 relative to subsystem 2 (after Marónski. 1991). several of the model assumptions appear. It is not obvious why Marónski (1991) did not apply appropriate constraints and then perform an optimisation of this model. to the extent of proposing and testing an alternative model for the hammer throw. Symbol denotes the rotation angle of subsystem 2. Furthermore. . he made no systematic attempt to outline a process of simulation evaluation.Simple models of the sports performer 219 Figure 7.9 Another model of the thrower-discus system that allows for the angular displacement of the implement-arm-shoulder-trunk subsystem (1) with respect to the rest of the thrower’s body (the pelvis-legs subsystem. He presented no experimental evidence to this effect. what occur in the best hammer and discus throws. indeed. to obtain linear velocities for the discus that approach infinity. Such velocities require the angular velocity of element (2) to approach minus infinity—a value never found in studies of human movement. to be oversimplistic and only a thorough simulation evaluation would reveal this. This could have addressed the issue of the suboptimal no switching and single switching conditions and whether these are.9). He therefore proposed an alternative model for the discus throw (Figure 7. 2). in which two rigid bodies represented the shoulder and trunk (1) and the remainder of the thrower’s body (2) respectively. Marónski (1991) gave careful consideration to some aspects of his model assumptions. As should be apparent from the previous paragraphs. in the lack of constraints on the angular velocities of element (2) and that of element (1) relative to (2). he showed that it was possible. less realistic for this event than for the hammer throw. Using the principle of conservation of angular momentum. However.
It is now necessary to consider those sports motions for which a more complex model is needed. they failed to carry out this relatively straightforward simulation evaluation. However. As this height was closer to that achieved by high jumpers with the same take-off kinetic energy. The increase in modelling complexity. not at.1 INTRODUCTION In the previous section. This simple model (developed for the Eastern roll and applicable also to the straddle technique) demonstrated that. the process of adding model complexity only when needed is a sound one and was also reported by Hubbard and Trinkle (1982) for their high jump model. at some stage in the modelling. so that the jumper was 6 cm above the bar when horizontal. using the quasi-rigid body model to investigate some specific optimum motions in the thrust stage of the hammer and discus throws (Marónski. simulation and optimisation process. 1992). and consequent increases in the complexity of the simulation and optimisation stages.4. results inevitably in a clouding of insight into the meaning of the results. It is not therefore clear what led them to the development of the more complex three-segment model—torso. thighs. the brush with the bar occurred before and after. for optimal partitioning. 7. the model . In Chapter 6. Although the authors mentioned that the results of their optimisations could have been compared with real jumps. However.3. a more complex model often becomes necessary. shanks (Hubbard and Trinkle. The insights that such simple rigid body models provide into the mechanics of sports movements more than justify their use. However. This showed the insights that such simple rigid body models can provide into the mechanics of sports movements. 1991). The lack of simulation evaluation prevents any systematic analysis of the changes to the model. the new model allowed clearance of a height 12 cm greater than the old for the same total take-off kinetic energy. the zenith of the jump.220 Mathematical models of sports motions 7. the rigid body model used by Hubbard and Trinkle (1982) to investigate the optimal partitioning of take-off kinetic energy in the high jump was mentioned.4 More complex models of the sports performer 7.5 CONCLUDING COMMENTS The simplicity of the quasi-rigid body model of the human performer used by Marónski (1991) allowed an insight into an important element of discus and hammer throwing technique and offered a possible improved model for better evaluation of the discus throw. optimal control theory was applied to a problem involving the motion of a sports performer. It is therefore justifiable only if the results are both necessarily and demonstrably a better approximation to reality.
high and triple jumping.2 LINKED SEGMENT MODELS OF AERIAL MOVEMENT It is perhaps not surprising that. It is also to be noted that in some of the models in the following section. Yeadon (1993) used a single rigid body model for simulation. the tilt angle (in the frontal plane) oscillated.g. the simulations did not include a systematic search for an optimum solution. although it was also more difficult to interpret the results. 1987). but not optimisation. The aerial phase of ski jumping (Hubbard et al. which include many routines in diving. in many cases because of the difficulty or impossibility of specifying a performance criterion. the author did not perform the simulation evaluations needed. data derived from film were used as a check on the accuracy of the simulations. Yeadon. In both modes. which suggests that twisting may be stopped simply by piking to change the body’s moment of inertia. discrepancies were reported for total twist and total somersault angles of 10% and 5%. the twist angle increased continuously. which Yeadon (1993) considered to be an indication that benefit might be derived from delaying arm adduction until the attainment of the quarter twist position. . and in many other models..More complex models of the sports performer 221 was more realistic. The general point here is that adding complexity can provide more realistic simulation and optimisation results. of the flight phase of twisting somersaults to obtain an analytical description of the possible free motions of such a body. gymnastics and trampolining and the flight phase of long. This showed there to be a theoretical possibility that a full twist could be produced during a plain dive simply by the use of asymmetrical arm movements.4. However. In the former. but inevitably makes their interpretation more difficult. Van Gheluwe (1981) also concluded from his simulations that the twist arose from arm movements during the aerial phase rather than being generated during trampoline contact. This showed there to be two such motions: the twisting mode and the wobbling mode. Angular momentum is therefore conserved. 1989) cannot be included in this assumption because of the vital importance of aerodynamic forces. so that the performer’s movements are regulated only by gravitational force. respectively. In the six-segment model proposed by Van Gheluwe (1981). are the most commonly modelled (e. with the exception of gait. They allow the simplification that the aerodynamic forces on the performer are negligible. whereas in the latter it oscillated. aerial movements. 7. An early model of aerial movements was the five-segment model of Pike (1980). for trampoline back somersaults with full twist.
11 Whole body angles: somersault ( . 1990a. Figure 7. .10 Eleven-segment model (after Yeadon. with permission). (reproduced from Yeadon. tilt (θ) and twist ( ). 1987).222 Mathematical models of sports motions Figure 7.
10. 1990b) will form the basis of the remainder of this section. However. wrists and ankles to the articulations of Figure 7. The same was true when the body was subjected to external forces causing tissue displacement. 7. The model has 11 rigid body segments. How the three-dimensional geometry of body segments is to be treated. The configurations between the segments are specified by 14 orientation angles.3 HANAVAN’S HUMAN BODY MODEL Hanavan’s (1964) work was a part of the USA space programme designed to improve the performance of self-manoeuvring spacecraft by establishing a mathematical model to predict the inertial properties (mass centre location and moments of inertia of body segments) of the human in several quasistatic postures. The asymmetrical location of internal organs was not . If. In general. 1987). 1964: Hatze. These models have been used in various simulations. and have been applied to technique coaching (see Yeadon. The model was based on experimentally determined mass distributions and the anthropometry of the person concerned. The non-inclusion of extra segments. and how. • • • • • • The number of segments required to model the particular sports motion being considered. 1987). which would have been possible by the addition of neck.More complex models of the sports performer 223 Further refinements of this model have been reported in a series of papers by Yeadon and his co-workers (for example Yeadon. like models of non-airborne sports motions.10. 1980. these aerial models do not require sophisticated muscle models as the movements are relatively slow. No account was taken of changes in inertial properties during a change in body position. The problems that such models have to address include the following.11).4. These mathematical models represent the body segments as geometric solids to estimate values for the inertia parameters of all segments. such as those of twisting somersaults. they do need to consider how the segments are modelled. variable densities within segments are to be accommodated. Consideration of three models (Hanavan. tilt and twist angles (Figure 7. Yeadon. while the whole body orientation is defined in terms of the somersault. How the degrees of freedom at each joint are to be represented or simplified. as shown in Figure 7. How personalised the model will be. was justified by the author on the basis that movements at such joints cannot be determined accurately from film data (Yeadon. Whether the rigid body representation of a segment is adequate. 1987).
The latter two points apply to all the models considered in this section. 1964). The model incorporated the following assumptions.224 Mathematical models of sports motions included. • • Figure 7. In reality. The rigid body assumption is necessary to reduce the indeterminacy of the resulting equations in a motion simulation. The regression equations for segment weights were valid for the Air Force population considered.12 Hanavan’s (1964) model (after Hanavan. this was a fit male population only. segments do not have uniform density or shapes as simple as those of Hanavan’s (1964) model. which are not necessarily coincident with the cardinal axes. but requires the accurate location of the axes of rotation. • The segments can be represented by rigid bodies of simple geometric shape and uniform density. Movements of the segments occurred about fixed joint axes. which probably accounts for most of the errors in the model. . This may well be true.
1 Comparisons of Hanavan’s model with cadaver results of Dempster (from Hanavan. the two trunk segments were elliptical cylinders. symmetrical body positions for which experimental results were available from 66 subjects for the whole body inertial parameters. For the vertical axis. while discrepancies in the latter were as high as 10% with an even greater number of errors for the foot (Table 7. Comparisons were also made between the mass centre locations and relative segment densities for model segments and the cadaver data of Dempster (1955).8 cm respectively of the experimental data. 1 964) . Twenty-five anthropometric measurements were needed to dimension the model. arising largely from oversimplified segment geometry and the constant density assumption. even ignoring the two worst positions.More complex models of the sports performer 225 The model consisted of 15 segments (Figure 7. the hand was a sphere and the other segments were all frusta of circular cones. where the experimental controls appeared to be poor. The errors in the moment of inertia values were greater. with only half of the values about the two horizontal principal axes being within 10% of experimental values. However. a discrepancy of less than 20% occurred for only half of the data.12) of simple geometry—the head was a circular ellipsoid of revolution.3 cm and 1. The errors in the average values of the former were quite low. The model was validated in a series of relatively simple. With the exception of one of the positions studied. The model had the simplicity and the small number of measurements needed to specify its parameters that the ‘keep it simple’ modelling principle requires. the values of whole body mass centre location were such that only 50% of the predicted model horizontal and vertical locations were within 1.1). except for the head–torso and upper arm. its weaknesses were the substantial errors in segment volumes and moments of inertia. It also did not permit movements Table 7.
1980).13 Hatze’s anthropometric model (after Hatze. it was dimensioned through 242 anthropometric measurements. Figure 7. its modelling of the dynamically separate shoulder girdle segments. . and the fact that segments had neither simple shapes nor assumptions about symmetry. The model had the same segments as that of Hanavan (1964) plus the two shoulder girdle segments. and made no attempt to model the dynamically distinct shoulder girdle segments. which Hatze (1980) estimated to result in a maximum error of 6%.226 Mathematical models of sports motions between the head and trunk segments. The major assumption is the necessary one of segmental rigidity. a limitation for sports motions. These included its allowance for sex differences through the use of different density functions and mass distributions.13) had several advantages over others then available.4. 7.4 HATZE’S ANTHROPOMETRIC MODEL Hatze (1980) claimed that his model (Figure 7.
The latter was used in preference to the ellipsoidal model of the head. In the buttocks.2. 1980).2 presents a summary of the comparisons carried out between model predictions and experimental measurements from the four subjects and from elsewhere in the literature. two trunk segments and buttocks were geometrically very complicated (see Hatze. 1980) . Lower legs and forearms were composed of 10 elliptical cylinders of equal heights and different densities. the density difference between males and females was taken into account. the thighs and upper arms were similar. These were attributed by Hatze (1980). swimming trunks trapping air in immersion measurements. The models of the shoulder girdle. Removal of these systematic errors (the author did not say how) resulted in the lower maximum errors shown in column (b) of Table 7. different definitions of the thigh segment between the author and Dempster (1955). at least in part. The maximum discrepancies obtained are shown in column (a) of Table 7. one female tennis player and one 12-year-old boy. each having a specified density. Validation data were reported from two young male athletes. The feet consisted of 103 unequal trapezoidal plates. Table 7. each having non-linearly varying density.More complex models of the sports performer 227 The segments in the model were subdivided into subsections of known geometric structure. The head-neck segment consisted of an elliptical cylinder to represent the neck and a general body of revolution for the head. Table 7.2 Summary of model errors (from Hatze. The hands were modelled in the grip position. 1964) resulted in a 31% error in the predicted principal moments of inertia. and consisted of a prism and a hollow half-cylinder to which an arched rectangular cuboid was added to represent the thumb. which Hatze (1980) claimed underestimated the mass of that segment by 23%. Hatze (1980) noted that the elliptical cylinder model of the lower trunk (Hanavan. to: the validating data. by this means the model incorporated density distributions along and across segments. but with modifications to represent the moving parts of the buttocks and the head of the humerus respectively.2. and the inability of the subjects to relax fully during oscillation experiments. thighs and calves.
Except for the cranium. the inertia parameters of which are standard. subdivided into subsegments (40 in total). • • 7. • It is overparameterised—the requirement for 242 anthropometric measurements. These limit the model’s versatility. Formulae for the inertia parameters and a full specification of a stadium solid were provided in Yeadon (1990b).15b) more closely resembles that of the thorax (Figure 7. for the other limb and the head subsegments. The author reported no comparison of the errors in the whole body moment of inertia about the vertical axis in which the largest errors might have been expected. The inertia values for the segments that these non-existent articulations connect are available from the model although they were not used in Yeadon’s simulations.15a) than does the elliptical section (Figure 7. like the model of Hatze (1980) but unlike that of Hanavan (1964).5 YEADON’S MATHEMATICAL INERTIA MODEL OF THE HUMAN BODY This model was developed for use in the 11-segment simulation model (see section 7. although Yeadon (1990) claimed that they can be regarded as adequate in the light of the good agreement between simulations and performance. .228 Mathematical models of sports motions The strengths of the model are clearly the very small errors reported between predicted and measured parameter values.4. The geometry of the body segments was represented as stadium solids.15c) used by Hanavan (1964) and others. wrists or ankles.16) in the case of the five trunk and the hand and foot subsegments or. taking 80 minutes to collect. the cross-section of which (Figure 7. the incorporation of the dynamically distinct shoulder girdle segments. The body segments were. The model seems to have been developed with no consideration of the ‘keep it simple’ principle. as truncated circular cross-section cones— effectively stadium solids with rectangles of zero half-width (t). as is evident from Figure 7.2) with the assumption of no movement at the neck. Full details of the segmentation are given in Yeadon (1990b). the body subsegments in the model of Yeadon (1990b) were represented as stadium solids (Figure 7. and the model does have some limitations. must also limit its practical use.14.4. it is debatable whether four subjects are sufficient to constitute a full model evaluation. However. the allowances for varying segment density and the degree of personalisation the model offered. There is no evidence that the author calculated the moment of inertia about the anatomical vertical axis for the shoulder girdle segments. The cranium was represented by a semi-ellipsoid of revolution. yet there is no clear evidence that such a level of complexity is necessary for the model’s purpose.
hand and foot. Figure 7. For the other stadium solids of the trunk. 1990b). The dimensioning of the model was provided by a series of simple measurements at the various boundaries of the subsegments (Figure 7. measured with a tape.14 Model subsegments (after Yeadon. (b) stadium. 1990b). were used to define most of the truncated cone subsegments of the head. which Yeadon . The boundary positions were measured using anthropometric calipers.More complex models of the sports performer 229 Figure 7. At the shoulder level of the torso. The model required 95 measurements to define it. It should be noted that the error in obtaining cross-sectional areas for these solids was reduced if the perimeter and width were used to define the geometry rather than the depth and width (Yeadon.16) (Yeadon. 1990b). (c) an ellipse (after Yeadon. arm and leg. 1990b).15 Cross-sections of: (a) thorax. so that the subsegment heights could be calculated. depth (h) was measured as the perimeter could not be. Further details of the measurements and geometry of the feet were given in Yeadon (1990b). The boundary perimeters. the boundary widths were measured.
1955). The evaluation of the model reported by Yeadon (1990b) involved three trampolinists—two male. Yeadon’s (1990b) statement that only total body mass is directly measurable ignores the fact that many segmental volumes and centres of volume can be easily measured and that Hanavan (1964) and Hatze (1980) used measurements of whole body moment . which is worse than the value obtained by Hatze (see previous subsection). were derived from cadaver studies (in this case Dempster. 1990b). Each of the major limb segments in Yeadon’s (1990b) model had a constant density as did the head-neck segment and the three trunk segments. The total body masses from the model were compared with those obtained by weighing.230 Mathematical models of sports motions Figure 7.16 Stadium solid (after Yeadon. The error was attributed to the effect of breathing on torso measurements. No attempt was made by Yeadon (1990b) to carry out any evaluation of the accuracy of the segment inertia parameters. The variable segmental densities in Hatze’s (1980) model are probably a closer approximation to reality. This is considerably more measurements than the 24 needed for Hanavan’s (1964) model but far fewer than the 242 required by Hatze (1980). one female. like those in both of the other models discussed in this section. claimed could be completed in 20 to 30 minutes. The density values in Yeadon’s (1990b) model. and resulted in errors close to 2% for all three trampolinists. This is a limitation of all of these models.
and the overparameterised model of Hatze (1980). simulating and optimising sports motions. This reduces both their complexity (an advantage) and their scope (a disadvantage).4. In this section. slightly sidesteps the issue. The models of Yeadon (1987). 7. In all other respects this model seems an excellent compromise between that of Hanavan (1964). 7. However.6 CONCLUSIONS Mathematical models of the linked segment representation of the sports performer are a necessary part of the overall process of modelling. used to investigate the nature and origin of airborne rotational sports motions. the use of linked segment models of the sports performer was considered. Later developments of these models will probably tackle this problem. that is.2 THE COMPUTED TORQUE APPROACH In some models. for example.5. These torques were those required . They should be adequately evaluated before incorporation into complete mathematical models of the sports performer. the torques have been specified relatively simply. Yeadon’s (1990b) argument. the associated problem of specifying the controls on the movements of those models will be considered. 7. the internal joint torques were calculated from inverse dynamics. and the related topic of modelling the body segments was addressed. that the evaluation of his model is effectively performed in the motion simulations he carried out. a topic that will form the subject matter of the next section. These models also require the modelling of how muscles move the body segments. the model has not had sufficient evaluation of its accuracy to allow its unreserved recommendation for general sports motion modelling.Models of skeletal muscle 231 of inertia in their evaluations. In the ski jump model of Hubbard et al. Such models should only be as complex as necessary for the motions for which they are intended.5.5 Models of skeletal muscle 7. how the driving torques at the model’s articulations are represented. the errors of which are too large and which is oversimplified for modelling and simulating sports motions.1 INTRODUCTION In the previous section. did not require muscle torques— instead the movements of the various segments were obtained from film of performances. It should be noted that this is not a problem that has been addressed by all simulation models. (1989).
While their argument that this is not sufficient as a simulation validation is acceptable. is to obtain these torques from models of skeletal muscle. This allows the . An alternative approach. especially in the early stages of flight as the jumpers sought to achieve stable flight configurations. which includes the aerodynamics of the jumper’s flight. The authors’ comment that a complete simulation evaluation requires a knowledge of joint torques as inputs and that these cannot be directly measured is correct..3 MUSCLE MODELS The airborne motions discussed above are. therefore. The inertial data and joint torques are used as input for a simulation. the authors presented a rationale through which complete validation would be possible. discussed below. Jumper joint torques. generally. lengths and moments of inertia are measured.232 Mathematical models of sports motions only to retain the jumper in a rigid body configuration. Turning to the problem of simulation validation. special cases. Unfortunately the authors did not report full details of this optimisation in Hubbard et al. and a 6% increase in jump distance.5. were possible for the Olympic champion. where only the rigid body maintenance torques had to be computed. The authors’ measurements of jumps at the 1988 Calgary Winter Olympics showed important relative movements of body segments. The torques required to change the jumper’s configuration and control his trajectory were treated as perturbations on the rigid body maintenance torques (Hubbard et al. it would nonetheless appear to have the virtue of being necessary and worthwhile. Commenting that the joint torques cannot be measured but only inferred from the method of inverse dynamics. such as the whole body angular and translational velocities. This showed that a 38% increase in flight time. Their simulations firstly investigated the effects of initial conditions. The closeness of agreement of the simulated and measured data can then be a measure of the model’s validity (Hubbard et al. on rigid body flights. 1989). necessitate the making of fast changes in segmental configurations. 1989). body configuration and trajectory are measured as functions of time throughout an entire flight. • • • Jumper body segment masses. as the forces acting on the performer are not large and do not. 7. the authors rejected the use of an evaluation exercise—in which computed joint torques would be used as inputs to the simulation model—as simply ‘playing back’ the torques through the model. The resulting simulated configurations and trajectory are compared with the experimentally measured ones. (1989).. This was followed by the use of an optimisation procedure to generate joint torques to maximise jump distance.
Essentially. The series elastic element lies in series with the contractile component and transmits the tension produced by the contractile component to the attachment points of the muscle. without the need to model the dynamics of skeletal muscle.17). • • The contractile element is made up of the myofibril protein filaments of actin and myosin and their associated cross-bridge coupling mechanism. The elastic elements will store elastic energy when they are stretched and will release this energy when the muscle recoils. with elastic structures within the crossbridges and the Z-line of the sarcomere contributing the remainder (Hatze. perimysium. The parallel elastic element comprises the epimysium. Muscle models range from the deceptively simple to the incredibly complicated. when the forces produced by the performer need to be considered.Models of skeletal muscle 233 segment motions to be represented by simple geometric formulae. . however. Such a schematic model of skeletal muscle generally has contractile. 1981). • Figure 7. this is not true when the performer is in contact with the ground.17 Schematic model of muscle based on Hill (1938). series elastic and parallel elastic elements (Figure 7. therefore requiring the modelling of muscles. almost all of them are derived from the model of Hill (1938). endomysium and sarcolemma. The series elastic elements are more important than the parallel ones in the production of tension. However. The tendons account for by far the major part of this series elasticity.
such that the muscles are either active or inactive—essentially this is a feature not of skeletal muscle but of a single muscle fibre. 1989). This viscous property enables them to absorb energy at a rate proportional to that at which force is applied and to dissipate energy at a rate that is time-dependent (see also Chapter 1).18) to make them reflect viscoelastic reality. more subtle. muscle models. The muscle models used in sports motion simulation vary in the number of elements they contain. The two-muscle models of throwing (Alexander. In all these. in a simplified but valuable model of jumping. the force output of which depended on the length and velocity of the muscle. The elastic elements in Hatze’s models did not depart radically from those of Figure 7. although none of them exactly reflects the physiological and biomechanical behaviour of skeletal muscle. They also ensure the return of the contractile elements to their resting position after contraction. this also applied to the parallel elastic element but with length as the dependent variable. Alexander (1990). used a single knee extensor muscle model. This consisted of only contractile and series elastic components. in which the contractile component force depended only on the speed of contraction. 1991) incorporated the influence of the length of the contractile component.4 A MORE COMPREHENSIVE MODEL OF SKELETAL MUSCLE The models of skeletal muscle developed by Hatze are widely reported in the biomechanical literature and their main points are summarised in Hatze (1981). other than in the introduction of damping (as in Figure 7. Essentially therefore. Their major restriction. The mathematics of these models is somewhat beyond the scope of this chapter. All of these models are relatively simple. 7. the elastic elements are important as they keep the muscle ready for contraction and ensure the smooth production and transmission of tension during contraction. the control is discontinuous (‘bang-bang’).5. The behaviour of a whole muscle is.17.234 Mathematical models of sports motions Biomechanically and physiologically. therefore reducing the risk of injury (Nordin and Frankel. and many more. The greatest departure from earlier models lay in Hatze’s treatment of the contractile component. lies in the modelling of their control. each had only a contractile component. however. . The seven muscle groups in the five-segment model used by Yoshihuku and Herzog (1990) to investigate cycling. The series and parallel elements are viscoelastic rather than simply elastic. They may also help to prevent the passive overstretching of the contractile elements when relaxed. fortunately. the series elastic elements were characterised by an exponential load-extension relationship.
Models of skeletal muscle 235
Figure 7.18 Muscle model of Hatze; symbols as in previous figure except: BE represents the cross-bridge series elastic element and PS the sarcolemma parallel elasticity. The parallel elastic element, PE, is represented by a viscoelastic springdashpot (after Hatze, 1981).
Instead of seeking simply to incorporate the length-tension and forcevelocity relationships, Hatze developed a mathematical model of a muscle fibre in which the force was a product of the state of the muscle before and during contraction (its ‘active state’), the degree of actin-myosin filamentary overlap and the velocity of movement between the actin and myosin filaments. This model was based on a hypothesis that incorporated both the sliding filament theory and an assumption that the energy transformations in the muscle proceeded in a chain from chemical to electrical to heat and work (Hatze, 1981). The active state model also incorporated the decrease in the relative concentration of calcium ions as the muscle fibre diameter changed, and accounted for the occurrence of non-linearities, such as myosin filament and Z-line collisions at short fibre lengths. The response of this model to various nerve impulse trains was presented in, for example, Hatze (1981) and was claimed by the author to be confirmed by previous experimental results. This could be considered to be a form of simulation evaluation. The remainder of the fibre contractile element model was simple in comparison. The length-tension relationship followed an exponentialsinusoidal relationship. Hatze (1981) also noted the need for a statistical (Gaussian) spread of fibre lengths to be incorporated in the whole muscle model. The velocity relationship is non-linear, and the model also has to account for the internal resistance caused by sarcolemmar deformation. The whole muscle model was considerably more complex. It allowed for a varying average stimulation rate and treated a varying number of stimulated motor units which are recruited sequentially according to their size. Further details of this model are beyond the scope of this chapter. Interestingly, the
Mathematical models of sports motions model’s behaviour was controlled by variations in the motor unit recruitment rate and the stimulation rate, as happens physiologically. However, in reality these variables are discontinuous, although they generate a smooth muscle response. This discontinuity was represented in the model by continuous normalised values for simplicity.
7.5.5 EVALUATION AND USES OF HATZE’S MODEL OF SKELETAL MUSCLE In an attempt to investigate and validate his model of skeletal muscle, incorporating those features of the previous subsection, Hatze (1981) reported a series of experiments carried out in relation to a model of the triceps brachii (Figure 7.19). The author noted that the model needed the values of a set of parameters to be estimated. This required a series of observations of constant maximum isometric torques at various muscle lengths, of quasi-stationary torque outputs at various activation levels and of linearly increasing torque outputs. On the basis of such experiments, with known moment arm and muscle length functions and assuming tendon resting lengths and minimum and maximum fibre inclinations, several important parameters could be estimated. These included the maximum isometric force, the ‘spreads’ (widths)
Figure 7.19 Triceps brachii model; symbols as in previous two figures except: is the muscle fibre pennation angle, maximum max, mean av, minimum min; subscripts 1–3 denote the three heads of the muscle (after Hatze, 1981).
Models of skeletal muscle 237 of the length–tension curves, and the optimal muscle lengths. The experimental details are faithfully reproduced in Hatze (1981) and considerable trouble was obviously taken to obtain these parameter values. However, it is arguable whether this constitutes a model or simulation evaluation and it is difficult to dispute the criticism often made of this model that it is overparameterised. The use of such muscle models in optimisations of sports motions is very limited. The study reported by Hatze (1976) contains many features of interest not only to the sports biomechanist but also to researchers in motor control. The study used earlier, but similar, models of the five relevant muscle groups. In it, the subject had to perform a kick with a weighted boot, used to slow the movement time and to represent an unfamiliar task. The movements were restricted to the sagittal plane, the pelvis was fixed and no movement was permitted at the ankle (see Figure 7.20). These and features of the target position served as constraints on the optimisation. This involved the search for the optimal muscle model control functions (of time) that could achieve the constrained task in minimal time. The times for the optimal and achieved motions were compared. The discrepancy between the two is shown as a function of the number of trials in Figure 7.21. This error, or discrepancy, decreased to a plateau. Beyond these trials, feedback was provided that involved the performer watching the film of his kick with the optimum motion superimposed (knowledge of performance). A further improvement then followed, as shown in Figure 7.21.
Figure 7.20 Kicking study with weighted boot and constrained knee and hip joint angles (after Hatze, 1976).
Mathematical models of sports motions
Figure 7.21 Results of kicking study, showing error function (actual minus optimal model performance) reaching an initial plateau through natural adaptation with increasing trials, then tending to a second, close-to-zero plateau with training using knowledge of performance (after Hatze, 1976).
Figure 7.22 Long jump simulation (after Hatze, 1983).
Another interesting finding was that the trajectories of the subject’s best (near optimal) and optimal (model) motions were almost identical, but the muscle activation patterns to control these motions were not. This was interpreted as unsurprising given that kinematically identical optimisations were found with substantially different controls; in other words, a range of optimal controls probably exists (see also Best et al., 1995). Hatze (1976) also claimed the model to predict the stretch reflex, as the knee flexors showed control activity before the knee reached its hyperextended position. This example, although interesting, is not a sports motion. The widely cited (e.g. Hatze, 1983) long jump example (Figure 7.22) also contained features of
Summary 239 interest. However, the optimal muscle torques in that simulation were not obtained through the use of Hatze’s muscle models but were estimated.
7.5.6 CONCLUDING COMMENTS The above subsections show clearly several aspects of modelling skeletal muscle and, indeed, of modelling in general. • First, the models used should be as simple as possible for the problem to be investigated, with a stepwise addition of complexity where required. This is evident in the approach of Alexander (1990, 1991) but not in that of Hatze (1981). Secondly, the parameters required to describe the model should be as few as possible and should be capable of being measured reasonably easily. Thirdly, the rationale behind the model must be carefully assessed before developing the model. Hatze’s muscle model gives a fascinating, at times inspired, insight into the process of mathematical modelling of physiological structures and their behaviour, which none of the other studies discussed in this section approaches. Likewise, the optimisation of a kicking boot motion provides valuable insights for the sports scientist. Such models have their place in the sports sciences. They are, however, far too complex to be widely used in practice to provide a means of technique improvement by the simulation and optimisation of sports motions. They show that the development of a model that is both sufficiently detailed to be an accurate representation of a sports motion and sufficiently simple to be comprehensible is a very difficult task indeed.
In this chapter, further consideration was given to the uses of computer simulation modelling in the biomechanical optimisation of sports techniques. This was done by close reference to two published examples, particularly their modelling, simulation, optimisation and simulation evaluation stages; these were optimal javelin release and optimisation of implement radius in the hammer and discus throws. The interpretation and explanation of graphical representations of optimisation and the use of contour maps to identify likely ways to improve performance were emphasised. Some aspects of simulation modelling of aerial sports movements were also covered. Three models of human body segment inertia parameters were compared and contrasted. The chapter concluded by evaluating existing models of human skeletal muscle and their use both in general computer simulation models of the sports performer and in establishing optimal sports techniques.
3. that is over 91. 6. 7.6 m) is obtained when the angle is about -8°. Specify which of these strategies you would recommend to such a thrower.8 m. using Figures 7.3. optimisation and simulation evaluation stages of the optimal javelin release of Best et al. to increase the range. Repeat exercise 1 for the hammer and discus models of Marónski (1991). and give the reasons for your choice. How might you perform a simulation evaluation for the example you chose in the previous exercise? 9. through the use of a table.3. This should include consideration of the assumptions of the model.7 Exercises . 7. and other release parameters as in Figures 7. 88. why the strategies to maximise the performance criteria that were outlined in section 7.6 and 7. You should bear in mind how easy the changes might be to implement and any likely effects on other release parameters. You should pay particular attention to the issue of simulation evaluation. You should show that other permissible strategies.2). the release angle of attack must be made more positive. and any optimisation performed. You should pay particular attention to the assumptions of the model and how these were evaluated. using Figures 7. the range of simulations studied. Specify. specify which angle should be changed. the three models of human body segment inertia parameters covered in section 7. 5.2 and 7.1 and 7. following alternative permissible arcs of constant radius and angular momentum.g. Compare and contrast.2 and 7.4.7.g. After reading one or more of the appropriate references (see subsections 7.5° release angle of attack (the minimum) and the corresponding release angle of 36°).3 are correct. Clearly explain. (1995). also what would be the maximum range that could be achieved simply by changing that angle? For the example of exercise 2. and the greatest range (just over contour line 78. your set of values should include the maximum and minimum values of both angles (e. pay particular attention to their suitability for use in the simulation of sports movements. Outline and evaluate the modelling. four different pairs of release angle and release angle of attack that would produce the same range (e.4. undertake a critical evaluation of a computer simulation of an aerial sports movement of your choice. for 88. 3. 2. Outline three possible strategies to optimise the release conditions for a thrower currently throwing with a release angle of 20° and release angle of attack of 36°. simulation. For each of the four angle pairs from exercise 2. 4. contour line 66).240 Mathematical models of sports motions 1. and in which direction.8 m.4. 8. from Figure 7. 20. result in a decrement in the performance criterion for the two throws.
England. 58–71. Journal of Biomechanics. methods and recent developments.J. (1989) The throwing events in track and field. Damping of javelin vibrations in flight. American Journal of Physics. Best. C. 136–195. 11. Journal of Sports Sciences. and Alaways. R. Hubbard. 6. International Journal of Sport Biomechanics.8 References Alexander.M.V (1938) The heat of shortening and the dynamic constants of muscle. Series B. Philosophical Transactions of the Royal Society of London. Boca Raton. A three-dimensional analysis of javelin throwing technique at the 1991 World Student Games. J. and Trinkle. Mathematical Biosciences.. C.. London. in Biomechanics: Principles and Applications (ed. Journal of Theoretical Biology. 7. R. WADC Technical Report. R. R. (1990) Optimum take-off techniques for high and long jumps.. (1992) Clearing maximum height with constrained kinetic energy. A. (1989) A multisegment dynamic model of ski jumping.N. and Komor. 169–174. Pretoria. R. 52. R. in Biomechanics of Sport (ed.McN. (1991) Optimum timing of muscle activation from simple models of throwing. Dayton. A. 3. Best. (1988) The biomechanics of javelin throwing: a review. and Laporte.J. USA. 1125–1132. 833–843. R. Journal of Sports Sciences. 269–286. USA.J. 150.T. Hubbard. 315–328.L. R. 207–221. Outline the main conclusions that you would draw from this chapter on the use of muscle models in a general simulation model of the sports performer. Wright Peterson Air Force Base. 258–274. & F. AMRL Technical Report. pp. M. Yeadon. H..C. M. 329. Journal of Applied Biomechanics. 99–135. (1980) A mathematical model for the computational determination of parameter values of anthropometric segments. FL. Bartlett. Dempster. Bartlett. L. R. R. (1981) Myocybernetic Control Models of Skeletal Muscle: Characteristics and Applications. Martinus Nijhoff. 3–10. C. 13.. Hatze. W. H. (1976) The complete optimisation of a human motion. 12. 1. Hatze. Spon. Dayton. H. Alexander. 64–102. The Hague. Bartlett. Proceedings of the Royal Society of London.M. H. and Morriss.R. University of South Africa Press. (1983) Computerised optimisation of sports motions: an overview of possibilities. M. (1987) Optimal release conditions for the new rules javelin. 28. 49. (1964) A mathematical model of the human body.P. (1997). (1993). M. (1982) Optimal initial conditions for the eastern roll high jump.W. R. Hill. International Journal of Sport Biomechanics. 13. . Hibbard. pp.Vaughan). Hatze. 76.J.Huiskes). 349–372. M. M. (1981) Aerodynamic effects on discus flight. and Best. E.C. and Trinkle. Bartlett. Wright Peterson Air Force Base. Hatze. 179–184. E. Series B. (1997) Introduction to Sports Biomechanics. OH. S. J. R. 1–38. (1955) Space requirements of the seated operator.M. 213–238. CRC Press. Journal of Sports Sciences. OH. M. Hubbard. 5. Journal of Applied Biomechanics.McN. Hubbard.L. Journal of Applied Mechanics. Frohlich. (1995) Optimal javelin release. 3–12. 55–159. Hanavan.A.References 241 10. Hubbard. USA. Hubbard.M. and Sawyer.
Journal of Applied Biomechanics. T. 58–71. Birmingham. in Report on the 1991 AAA/WAAA National Championships Volume 1—The Throws (ed. 462–497. Occupational and Athletic Aspects (ed. (1990b) The simulation of aerial movement—II. Soong. in Report on the 1991 AAA/WAAA National Championships Volume 1—The Throws (ed. Pike.Van Gheluwe and J. (1991) Optimal distance from the implement to the axis of rotation in hammer and discus throws. Dekker. C. Ellis Horwood.Hollander. R. Morriss.L. (1984) Applications of Optimal Control Theory in Biomedicine. R.M.. Journal of Biomechanics. (1990a) The simulation of aerial movement—I. R. Cited in Marónski.242 Mathematical models of sports motions Jia. 496–497. 67–74. (1987) Theoretical models and their application to aerial movement. pp. Journal of Biomechanics. (1991) The biomechanics of the hammer throw. (1991) The biomechanics of the discus throw. 24. New York. Swan. Lea & Febiger.W.M. B. Viitasalo. W. (1988) On-line measurement of kinematic characteristics in javelin throwing. 23.Bartlett).J. Netherlands. 59–66. PA. (1989) Aerodynamics and throwing analysis of javelin. M. V. Clarendon Press. Unpublished doctoral dissertation. Yeadon M. 3.A. A. (1993) The biomechanics of twisting somersaults: Part I rigid body motions. British Athletic Federation. and Bartlett.N. Yeadon. A mathematical inertia model of the human body. G. This provides a simple example of the application of static optimisation in sports biomechanics. 1069–1079.E. 187–198. Bartlett.J. Journal of Biomechanics. (1977) Javelin dynamics including body interaction. and Zogaib. Hong Kong. Pennsylvania State University. and Sawyer. 24. . Journal of Biomechanics.R. Red. Fizkultura i Sport. USA. (1991) Optimal distance from the implement to the axis of rotation in hammer and discus throws. Chichester. R. A. Journal of Human Movement Studies.Huijing and G. Amsterdam. (1989) Basic Biomechanics of the Musculoskeletal System. pp. Journal of Applied Mechanics. and Korjus. P.M. Karger. M. England. Van Gheluwe. R. T. Switzerland.de Groot. R. D. M. M. Yoshihuku. in Human Body Dynamics: Impact. J. Free University Press. Tutjowitsch.P.J. Philadelphia. (1981) A biomechanical simulation model for airborne twist in backward somersaults. England.Ghista). (1969) Theory of Sports Throws. R. Q. Oxford. Basle. England. Journal of Sports Sciences. in Biomechanics XI-B (eds G. USA. (1984) Mathematics in Sport. M. Yeadon. 7. in Current Research in Sports Biomechanics (eds B. 11.M. Communication to the Fourth Asian Congress of Fluid Mechanics.T. 23. (1990) Optimal design parameters of the bicycle-rider system for maximal power output. Y. R. 999–1005.R.-C. W. Yeadon. The determination of orientation angles from film data. British Athletic Federation. Journal of Biomechanics. and Frankel. W. Nordin. 5–20. (1982) Biomechanical analyses and applications of shot put and discus and javelin throws.N. Moscow (in Russian). N. Marónski. Townend. (1980) Computer simulation of a forward. 12. 44. PA. Lindsay. (1995) Optimal javelin release. and Herzog. pp.A. full twisting dive in a layout position. 23. 583–587. 999–1005. Birmingham.R.9 Further reading Best.Atha).van Ingen Schenau). Bartlett).H. 86–106.R.S. M.J.
R.Atha). in Current Research in Sports Biomechanics (eds B. Yeadon. pp. Karger. Basle. Pretoria. . University of South Africa Press. H.Van Gheluwe and J. A bit out of date. This provides a good overview of simulation modelling of aerial movements. although it is a little out of date. (1981) Myocybernetic Control Models of Skeletal Muscle: Characteristics and Applications. M. but an extremely useful summary of much of that author’s work on skeletal muscle modelling and the underlying process of modelling biological structures. (1987) Theoretical models and their application to aerial movement. 86–106. Switzerland.Further reading 243 Hatze.
and how it might be corrected. why it is a fault. sports biomechanists have not generally had the same difficulties in having the relevance of their research recognised by coaches as other biomechanists have had in convincing clinical practitioners of the value of gait analysis (e. However. Brand.1 The importance of feedback If. by using the methods described in Chapters 5 to 7. This will require feeding back our results to show what the fault is. 8. Cappozzo. then we must communicate that information to the athlete and coach. some of the comments of Brand (1992) are also relevant to sports biomechanists. 1983). we have systematically identified a flaw in an athlete’s technique that is preventing optimal performance. . After reading this chapter you should be able to: • outline the fundamental points that must be satisfied for biomechanical feedback to the coach and athlete to be relevant • describe the strengths and weaknesses of the various ‘technique assessment models’ and their limitations in feedback • appreciate the important roles played by technique training and skill acquisition in the process of modifying a sports technique • define the three stages of learning a sports technique and assess the relevance of each to technique improvement • understand some of the issues that must be addressed in seeking to optimise the provision of biomechanical information to the coach and athlete • give examples of the use of computer-based feedback and outline likely developments in this mode of information provision. 1992. Fortunately.8 Feedback of results to improve performance This chapter will provide you with an understanding of how the results of biomechanical studies of sports techniques can be communicated (or fed back) to the athlete and coach to improve performance.g.
if any. and this may be especially true for kinetic variables (Gregor et al. Despite this. The frequent calls for rapid feedback and more feedback from both coaches and scientists (e. to fulfil an educational role. It should be self-evident that the feedback used should involve the right information at the right time and in an easily understood format: the speed of feedback and its presentation and interpretation are all important. of feedback nor of how and when it should best be presented. and the view that information feedback is the single most important variable (excluding practice) for learning (e. . which have been addressed in the last three chapters. of course. point to some future research directions in which sports biomechanists should be involved within interdisciplinary teams. for example using detailed quantitative video analysis. but also about the feedback of results to coaches and athletes from well-designed experiments (Chapter 6) or simulation modelling (Chapters 6 and 7). Feedback may be provided.g.. Some aspects of technique modification may require longer term (months or years) research studies to provide the necessary scientific basis for a correct technique model. 1989).. There are. there is often a great deal of information available. 1991). Providing more information does not always improve performance and may cause confusion.g. Medium-term feedback (days or weeks) is likely to be more appropriate when seeking to change a technique. in turn. very few studies have directly addressed the issue of feedback to athletes and coaches of information from biomechanics research into technique in sport. Dillman. These points clearly raise issues not only about fundamental research. However. such as sport. Although many of these theories have been developed for discrete laboratory tasks and have not been adequately tested on real world tasks. The use of such feedback needs to address relevant motor learning theories. they do provide some evidence to which sports biomechanists should attend.The importance of feedback 245 These include: • • • the need for accurate and reproducible results for the results to provide information that is not directly observable by a skilled coach for the results to relate clearly to differences between good and poorer performance. 1992). These. but it is not clear what should be provided. especially if the information presented offers no clear solution to the problem identified. Some forms of feedback may be immediate (seconds or minutes). 1989) often do not pay heed to the effects. other reasons for providing biomechanical feedback to coaches and athletes other than to remedy technique deficiencies to improve performance. for example measurements of running speed from photocells or simply replaying a video recording of a performance. for example. on which this chapter focuses. Schmidt. nor how (Gregor et al.
Schleihauf. the S-shaped path of the fingertip and the path of the fingertip relative to the rotating trunk (after Liu et al. One example relates to how propulsive forces are generated in swimming. This incorrect view was transformed by research that showed that swimmers’ hands made an S-shaped pattern of an inward scull followed by an outward scull (Figure 8. Armed with this information.246 Feedback of results to improve performance There are many examples in which erroneous information feedback has been provided to athletes and coaches.1). swimmers should pull their hands backwards in a straight line below the mid-line of the body using drag as the propulsive force (as in the straight line of Figure 8. in the front crawl. Schleihauf and others (e.. to optimise the pitch angle. making use of lift and drag forces. The pitch of the hand (its orientation to the relative velocity vector with the water) plays an important role in this respect. showing a hypothetical straight line pull.1). these sideways hand movements were shown to maximise force production by using the hand as a hydrofoil. 1979). the view of coaches had been that the hand acted as a paddle and that. Before the research of Counsilman.1 Hand paths relative to the swimmer. coaches switched to teaching a ‘feel for the water’. 1993). emphasising the sideways sculling movements of the arm.g. More recent studies using simple models of the Figure 8. . From fluid dynamics testing.
Technique assessment models and feedback 247 swimmer (Hay et al. 8. but also on identifying the ‘target performance’. The ways in which this can be done. The mediallateral motion of the hand relative to the rotating trunk involves the swimmer sweeping the hand away from the trunk in the first part of the pull and towards it in the second (Figure 8. experimentally.2 Technique assessment models and their limitations in feedback To make meaningful statements about the technique of an athlete and how to improve it. . we noted in Chapters 5 and 6 that a model is needed against which we can compare that technique and which will help in improving it. video or cine) parallel recordings (e. 1997) have shown that much of the sideways movement of the hand in the front crawl is attributable to body roll. in the context of feedback to improve performance through changes in technique. that body roll had a substantial influence on medial-lateral hand movements.3. An important requirement for sport scientists is. to improve technique..g. We need models to allow us to compare techniques. This section will address these requirements from the perspective of the use of technique assessment models in the context of performance feedback. This contradicted the previous research that had led to erroneous coaching beliefs about the relative motion of the hand. are the topics of technique training—vital for a new technique to be refined—and skill acquisition—necessary for the relearning of a technique. to be able to construct and use such ‘technique assessment models’ of the events they study and to be able to devise the most appropriate model for their purposes. Payton et al. hierarchical models) computer simulation models coaching analysis charts. These topics will be considered in section 8..g. The effectiveness of any feedback will depend not only on presenting the current performance of the technique. Also related to the fundamental issue addressed in this chapter. computer stick figure displays) ‘textbook’ technique (sometimes known as ‘natural language’ models) graphical models (e. therefore. to develop training methods. include the use of: • • • • • • • live demonstrations of performance serial recordings (e.1). Liu et al. (1993) showed. and to aid communication.g. 1993.
they require far deeper information about the technique to be known by the coach if this approach is not to degenerate into simply copying the technique of a more successful performer. to show an athlete how to perform or modify a technique.2 SERIAL RECORDINGS These include video tapes and cine films (see Bartlett. They require some interpretation. they can be subjective. i.3b).e. Again. 1997). For example. 1997) or. method for feeding back the results of our analyses to athletes and coaches.4a) even if it was filmed using two horizontal cameras. there is a need for the athlete or coach to be able to identify technique errors and how to correct them in the context of a deeper technique model. from computer-generated images such as stick figures (Figure 8. they presuppose a deeper technique model. they also require interpretation.248 Feedback of results to improve performance 8.3a) or solid body models (Figure 8. 8.2 Serial (frame by frame) solid body model display of a javelin throw.2. For example. they allow repeated study and they add the very useful concurrent representation of the movement. They do permit repeated study. Furthermore. if most timeconsuming. As with serial representations. By concentrating only on parts of the body.2).5 and Chapters 6 and 7). more commonly. so that simulated and actual performances could be compared (as in Figure 6. this would involve a computer simulation model (section 8. Only one picture is viewed at a time. However.2. ideally. Figure 8. in which the technique can be viewed from any chosen viewing direction. . javelin coaches can concentrate on the important alignment of hip and shoulder axes (Figure 8. frame by frame or field by field (Figure 8.4b) and hammer coaches can focus on foot placements with respect to centre of mass and hammer head positions. Many sports biomechanists have found this to be probably the most useful.2. hammer throwers and their coaches can see the throw viewed from above (Figure 8. Particularly useful in technique feedback is the use of computerised three-dimensional image-based motion analysis (see Bartlett. in other words. 1997). this approach still relies on the existence of a technical model of the event. depending very much on the coach. 8. but have to be studied serially.1 LIVE DEMONSTRATIONS These have their use in the field.3 PARALLEL REPRESENTATIONS These can be obtained from multiple-exposure single-plate photography (see Bartlett.8). Clearly. the computer software can show aspects of the technique that would not have been revealed even by an appropriately placed camera.
These models have little practical use in the process of identifying and eradicating technique faults. (b) solid body model of a javelin thrower. Examples can be found in almost all coaching texts in which a sports technique is described in detail.2. and often contain too much information. Such models are often hard to digest.3 ‘Parallel displays’ of: (a) a javelin thrower—stick figures. particularly where complex movements are involved.4 TEXTBOOK TECHNIQUE Historically.Technique assessment models and feedback 249 Figure 8.2 has been displayed together on this computer display. Each of the frames from Figure 8. 8. the ‘textbook’ technique served as the model technique against which others were evaluated. .
2.5 GRAPHICAL (DIAGRAMMATIC) MODELS These break the movement down into simpler elements. (b) hip (thick black line) and shoulder (thick dashed dark grey line) axes alignments from above for four key events in a javelin throw.250 Feedback of results to improve performance Figure 8. possibly hiding information until it is needed while still . the hammer head trajectory is also shown. The long light grey lines are the javelin and the light grey circles and connected lines are the feet. By doing so. with the thrower and hammer shown only for selected frames for clarity. they reduce complexity. 8.4 Selected displays of: (a) a hammer throw from above.
Technique assessment models and feedback 251 maintaining the overall structure of the movement. however. The two main types are described below. It can often provide a strong theory-based technique model to underpin other more field-based or computerised approaches. Hierarchical technique models These were discussed in detail in Chapter 6. they are. The menus would ensure that only an ‘easily digested’ amount of information was presented. The links between the layers of the model (the lines joining the boxes) may not be apparent. to date. . They do allow hierarchical organisation with different levels on separate pages or sheets. particularly for those not familiar with the movement represented or the use of such models (see. for example. this difficulty can be minimised if the rules summarised in Figure 6.4). A schematic representation of part of a hypothetical menudriven system is shown in Figure 8.3 are used.2). in which information would be organised to enforce the use of a hierarchical structure and to hide information. However. Menu-based systems These would be a logical and fully computerised extension of hierarchical models. largely non-existent (see also section 8. with the user dropping down to further levels of the model as required. Figure 6. The usefulness of this approach in conjunction with statistical modelling was considered in Chapter 6.5. They can produce far too much information on one diagram.
many of the issues associated with computer simulation modelling and optimisation (Chapters 6 and 7) are relevant here. this time with ‘show previous level’ allowed. However. Here. etc.8). Some evidence supports the idea that the best feedback involves the presentation of the target and current techniques in the same form.e.g. the user can choose to ‘go to model links:’ to access a submenu which.5. The structure of the model should be carefully considered. joystick.2. computer simulation models offer a powerful tool for technique improvement. controlled by a mouse.2. The model should seek to manage detail and establish clarity. 1989). and re-displays the menu. They contain some— but not much—justification of the points highlighted (see Figure 8.. We will return to this topic briefly in section 8. Choosing from the submenu reveals the next level and hides the previous level. Hierarchically structured graphical models have the potential for easy Figure 8. for example both as computer graphic displays (Daugs et al. 8. They are relatively easy to use for quick field or video analysis. (i. Other levels of the model are hidden from the user who interacts with the model through the pointer. would explain why ball release speed=run-up speed+speed added during delivery. Selection of the latter would reveal the next level of the model for ‘work done’. (a) The top level of a hierarchical technique model for generating ball release speed in cricket. Selection of the former would do likewise for ‘type of action’. Figure 6. 8. The most appropriate technique assessment models should be used (natural language is the least useful).6). .8 CONCLUDING COMMENTS All useful feedback to improve the performance of a technique requires a target performance against which an athlete’s current performance can be compared.5 (Previous page) Schematic representation of a menu-based system for a technique assessment model.6 COMPUTER SIMULATION MODELS By providing a direct comparison of the current performance against what it could be if the technique was changed (see e. in this case. the links between the boxes are justified). (b) The menu for user-interaction: the ‘show previous level’ function is not available for the top level of the model. etc.7 ANALYSIS CHARTS These have been claimed by their originators to be of great use to coaches in the evaluation and improvement of technical performance.2.252 Feedback of results to improve performance 8. They require lots of knowledge (hence other technique models) to develop. the user has chosen to ‘show next level for:’ in this case either ‘type of action’ or ‘work done’.
with permission). 1989.Technique assessment models and feedback 253 Figure 8. .6 Coaching analysis chart for the long jump (reproduced from Tidow.
i. All intelligent coaches must be aware that the optimal motor pattern for their athletes will evolve within these physical limits and may not. for example javelin or hammer throwing. 8. if based on a deeper model of the technique. • The essential features of a particular technique necessary for achieving a high standard of performance—this requires a theory-based technique model. conform in every detail to an athlete of different morphology but similar performance standard. Computer simulation and optimisation theoretically allow direct comparison of current and target techniques. usually assisted by slow motion video replays and increasingly supplemented by computerised biomechanical analysis and modelling. strength. or for the growing athlete temporarily. racket sports. Coaching analysis charts. therefore. let alone to athletes of different standards of performance. we require not only the presentation of the current performance but also instruction on the target that the training is seeking to achieve (Daugs et al. An important role of the coach is to guide the athlete in skill acquisition or technique modification to eliminate faults. the coach needs at least to be aware of the following. How to recognise these features in performance. Such morphological limitations as lever lengths or height are permanently. that much of the training required to learn or to modify such techniques will involve the acquisition of these skills. It is possible to define the goal of technique training as being to develop the optimal movement pattern to achieve the performance goal within the existing. therefore. This is the function of much of the training for the technique-dominated sports. such as gymnastics and the field events in athletics. for the feedback provided to be useful in improving technique in training. unalterable morphological limitations of the athlete. 1989). body weight and power.254 Feedback of results to improve performance management and informative display of such complex information. can offer a very useful field method for coaching feedback purposes.e. gymnastics routines. pole vault. and physiological ones such as speed and endurance can.3 The role of technique training Many sport techniques involve very complex motor skills. be eliminated or reduced so as to facilitate better technical performance. To do so correctly.. Other morphological limitations such as flexibility. learning of the required movement patterns to perform the event. As noted in the previous section. and must. How to discriminate between a desirable technique and the highly individualised stylistic variations that are seen in performances of athletes • • . and constant attempts to improve them. It follows. unalterable.
For example.3.1 LEARNING OR RELEARNING A TECHNIQUE Sports techniques can seriously break down under the stress of competition. even under the stress of competition. What is vital here is to ensure that the athlete is capable of manipulating his or her arousal level. The athlete will naturally want to test the newly acquired technique in competition and the coach can help prevent overarousal by ensuring that a correct goal is set and worked towards. so as to perform at or near to his or her technical optimum. Also vital is the willingness to update the model in the light of valid and completed biomechanical research. Careful attention to the general detail in the preceding three points can avoid gross errors and time wasting. it is generally true (e. Although ‘negative transfer’ can take place between very closely related skills. but lacks mobility (especially in the lumbar-sacral region). The pronounced stylistic variations in their throwing (using the same basic technique) follow quite logically from these structural differences. massed or distributed practice. These stylistic variations may be due to morphological adaptations or poor skill acquisition. or may have bowled in cricket (a similar crossover step). A sound biomechanical model of the technique used to achieve good performance is absolutely necessary for the technique coach at any level.g. although the evolution of a new and potentially superior technique will obviously need to be seriously studied (e.g. The issues of whole or part learning. Positive transfer can be helped by valid and comprehended . Rarick. the pole vaulter some gymnastic background. The current morphological and other limitations of the athlete and what adaptations might need to be made to the ‘standard technique’ to achieve an optimal movement pattern for the athlete. Few sports performers will approach a new skill with no relevant prior movement experiences. while the other is very flexible but possibly lacks some strength or speed. The need for flexibility in administering the learning of this model is equally crucial. and fault recognition or correction will then be briefly discussed. The three phases of learning a complex motor skill are well established and only a summary of these will be considered here. but not to be sidetracked by the stylistic variations of a new champion.The role of technique training 255 in that event. comparison of the techniques of two top female throwers might suggest that one is very powerful. As an example. the novice hurdler may have running or jumping experience. and an anxious athlete may not be able to perform at an appropriate technical level. the Fosbury flop high jump). 1980) that related movement experiences facilitate the learning of a new technique. • • 8. the budding javelin thrower will usually have thrown a ball with an ‘overarm pattern’.
In diving. with appropriate . negative transfer. Errors that are stabilised into the athlete’s movement pattern now will be much more difficult to remove later. faults may be due to such factors as poor motor ability. First (verbal-cognitive) stage of learning In this stage athletes will rely greatly on their coaches for verbal instruction. for example. poor environment. This is the stage of learning when errors are easiest to correct. When correcting faults at this stage. misunderstanding the movement. It is generally agreed that feedback is most useful at this stage of learning and that some visual form of feedback will have the best effect owing to the nature of the learning stage. as the neurophysiological ‘grooving’ of the movement pattern is not yet established. may have caused the diver to acquire excessive forward angular momentum. At this stage of learning. 1989). proprioceptive cues and be given while the ‘feel’ of the performance is still fresh in the mind of the athlete. although the coach. can still help to correct faults. or poor timing of technique training relative to the athlete’s age (Dick. poor demonstrations. Video replays should now be used in careful combination with useful. coaches will need to know why they arise. by careful observation. from positive and negative transfer respectively. a poor entry position may have its cause in the take-off. The correction is made to the take-off and the rest may then follow. where a forward lean of the trunk. Second (motor) stage of learning In this stage the athlete now relies on kinaesthetic cues (proprioceptive feedback) as the number of errors made is reduced and the technique begins to be integrated. for valid models to imitate and for feedback that will allow the correction of any gross errors in technique that will be presented at this stage. fear of injury. but a high level of good. The feedback is now intrinsic. The knowledge of performance (KP) or knowledge of results (KR) discussion will not concern us here. Generally. The easy availability of video equipment makes this no longer a major problem. The correct ‘feel’ can then be sought in the next rehearsal. there are times when the elimination of a technique fault may require the performer to relearn the correct movement patterns from the start.256 Feedback of results to improve performance analogies. Obviously. They can then set out to eliminate or remedy the cause of the fault rather than reduce its perceived effects. this stage of learning is not applicable to highly skilled performers seeking to improve their established technique. athletes seeking to modify or relearn a skill to eliminate defects in technique will also benefit. Obviously. and suffer. intelligent feedback (verbal cues) will facilitate learning of a reasonable movement pattern.
If no errors are present. inability to reproduce training technique in competition (wrong arousal level perhaps owing to incorrect goals or a failure to learn stress reduction techniques). whereas distributed practice allows the rest period to be as long as. 1991). he or she now obtains the maximum of information from the minimum of cues—such as a skilled shot-putter whose movements up to the end of the glide will follow from ‘looking at the rear of the circle’. Proprioceptive information from the stretch receptors of the appropriate muscles will provide such feedback and the further advice to ‘look at the rear of the circle’ will keep a simple cue in mind that will serve to integrate the whole technique. outside the context of the overall pattern.e. Schmidt. you should refer to a text on motor learning (e. For further details. or adaptations to some injury. which is an important point when seeking to remove faults from deeply ingrained techniques. so that greater speed or range of movement can lead to improvements in current technique. Singer (1980) . if necessary. For example.g. no ‘torque’ in the trunk).3. they will be due to faults in the learning process (bad coach or poor athlete). a shot-putter is perceived as performing badly owing to landing at the end of the ‘glide’ with both hips and shoulders pointing sideways (i. As a skilled performer. Errors perceived now are extremely difficult to correct. If they are errors. any improvement can be sought only from reducing the morphological limitations of the athlete. or longer than. each trial. Final (autonomous) stage of learning In this stage the athlete has a stable movement pattern.The role of technique training 257 changes. The link between appropriate cues and the athlete’s kinaesthetic awareness is of particular value in eliminating faults from a well-learned technique. Some of the issues most pertinent to training to improve technique are briefly addressed below. Massed versus distributed practice Massed practice provides little rest between trials in a training session. once the final learning stage is reached. 8. If the athlete is flexible. this is perhaps best corrected by maintaining the hip position and having the shoulders lag by 90°. with or without errors.2 HOW TO PLAN TECHNIQUE TRAINING Several issues need to be addressed when planning a technique training programme. Results as to which is better are inconclusive and are usually based on fairly simple tasks where practice is difficult and tiring. not only for initial learning of a technique but also in refining it to remove perceived flaws.
particularly for highly skilled athletes. If this also applied to sports movements at high skills levels. in the autonomous stage of learning. javelin release speed and angle and what these would have been for an optimal throw (Hubbard and Alaways. 1993). mental practice—with appropriate guidance and analogies—can help an athlete to rehearse the effects of changing a technique. automate stereotyped parts of an overall movement (Schmidt. and kinetic data from force pedals (e. In the context of correcting faults in a technique. The components here are such things as running. Broker et al.. however. learning time is reduced’ (Dick. 1991) provides evidence that summary feedback of results (after several practice trials) provides better results in the retention phase of learning than does immediate feedback provided after each trial (Figure 8. Mental practice Mental practice (also known as mental rehearsal) is increasingly recognised as effective. Although no consensus exists on how mental practice works.258 Feedback of results to improve performance suggested that distributed is better than massed practice. 8. Part practice can. flight.g.g. Again. In this form of practice. 1991).g. Dick (1989) suggested massing at early stages of learning. Schmidt. The need to relate the part to the whole is. There is probably a need to use both whole and part practice in most sports. Research has shown that when learning parts of a technique. Schmidt. it is now possible to feed back rapidly information relating to. the athlete mentally rehearses the skills to be learned or relearned with no obvious physical movements. crucial and Sage (1977) remarked that the ‘most important characteristic of a motor skill is its wholeness’. considerable evidence supports its effectiveness in the autonomous stage of learning at least (e. then sports biomechanists . which was supported by Sage (1977) and by Fitts and Posner (1967). the skill is often divided into several meaningful units for part practice. 1989). it is necessary to relate each to the whole technique: ‘If the first component learned is one that unites as many parts as possible of the final technique. The motor learning literature (e. Generally this is not proved. Massed practice is also good for high skill level peaking. 1989). for example. 1991). jumping. Whole versus part practice Because of the complexity of most sports skills. For optimum effectiveness.4 Information feedback and motor learning In a training context.7). landing: e. this suggests the usefulness of part practice. a mixture of mental and physical practice should be used. the four ‘phases’ of the long jump.g.
Research of this nature would be valuable in helping athletes to learn and incorporate modifications to a movement pattern. filled circles. Also. therefore. that feedback must be provided within minutes (e. at present.7 Comparison of immediate and summary feedback (as knowledge of results. there is insufficient evidence. KR) for a discrete task. what the implications of this are for technique training (and other training). Daugs et al. Hubbard. Many studies of feedback during technique training relate to early learning of skills. about whether this is general for sports tasks. and whether the effects are beneficial to performance or Figure 8.8). (1993) for the learning of modifications to pedalling technique by inexperienced cyclists (Figure 8. both (after Schmidt.g.g. immediate feedback. this has not yet been demonstrated. 1989) may not apply to more skilled performers. There are clearly many unresolved issues relating to optimal feedback to performers and coaches of sports biomechanics information. summary feedback. Collaborative research between the sports science disciplines might also seek to identify if changes to the technique of a highly skilled performer can be made successfully. Although no difference between summary and immediate feedback was reported by Broker et al. filled squares.Information feedback and motor learning 259 might need to amend their provision of feedback during training sessions. however. there is little empirical research to support this. Biomechanists and motor skill experts can beneficially combine to research such topics and to establish whether motor learning paradigms for simple tasks do generalise to more complex ones. 1993). . Published results relating to video feedback and the sequence in which current and target performances are presented (e. 1991). although it has been hypothesised that the usefulness of feedback decays rapidly with time and. Open circles..
while the latter would favour much more realistic solid body presentations. 1989).. while others have indicated the superiority of real representations (Daugs et al. injury prevention. 1993). For example. immediate feedback (after Broker et al. computerised stick figure displays.8 Comparison of immediate and summary feedback for a sports task.5 Use of compu ter-based feedback 8. The former would support the use of.. for example. filled diamonds.2. Although it remains difficult to separate the direct effect of biomechanics feedback on the performance of a sports technique from other effects. this is an issue worth revisiting for more thorough investigation by researchers in sports biomechanics and motor learning. there has been little research to establish the most effective ways in which information should be presented to achieve the required outcome of improved performance even. some researchers have found an increase in performance retention with increased abstraction.260 Feedback of results to improve performance Figure 8. the use of three-dimensional computer graphics has now become widespread in biomechanical feedback to sports practitioners.5.1 OVERVIEW As discussed in section 8. There has been far too little research into these areas (e. . summary feedback. 1985). Again. Petray and Krahenbuhl. 8. in terms of the best degree of abstraction of the graphic image. Open squares. for example.g.
Neither group of investigators reported any evaluation of whether the feedback of such information to athletes and coaches had any benefit in improving technique or performance.g. Lapham and Bartlett. 1976). however. the feedback was immediate. However. 1987) have been used to teach and correct technique in several aerial sports. 8. no evaluation of the usefulness of the feedback given to coaches and performers has yet been reported. Lapham and Bartlett (1995) surprisingly found no reports of the development of an expert system to provide biomechanical advice to athletes and coaches on problems of technique. The use of real-time computer simulators in skills training is .2 THE USES OF COMPUTER SIMULATION AND OPTIMISATION IN FEEDBACK The uses of computer simulation and optimisation of sports movements was discussed in Chapters 6 and 7 (see also Hubbard. no evaluations of the information fed back to sports practitioners have been reported for the long jump study of Hatze (e. 1983). Hatze. The second group has found that the top British javelin throwers find the feedback of information derived from quantitative analysis of film to be more valuable than the results of the researchers’ computer simulations. (1990). Similarly. An expert system in this context would involve a database of available quantitative information on a technique and on body characteristics and qualitative information on the technique. a way of matching that data to the expertise (an ‘inference engine’) and a user-friendly interface (Lapham and Bartlett.Use of compu ter-based feedback 261 An ‘expert system’ is a computer program that simulates the actions of a human expert. Yeadon. In this context. 1993). 1995). it is noteworthy that the US Olympic team no longer routinely uses in training the javelin feedback system reported by the first group. It consists of a great deal of specific knowledge (data and representations of the rules used by the expert). The development of such systems requires fundamental research.g. Hay (1989) considered there to be little reason to doubt the value of such systems in providing biomechanical advice to coaches and athletes. in the latter medium-term. 1989. The simulation models of Yeadon (e. In the former case. in which sports biomechanists should be involved. The provision of information relating to javelin release speed and angle and what these would have been for an optimal throw has been reported by Hubbard and Alaways (1989) and Best et al. 1995). and that they could have a profound effect in sport.5. although evaluation of the provision of knowledge of performance was implicit in his kicking boot study (Hatze. The system’s inference engine would match these data with expertise—the rules and probabilities that emerge from analysis of how experts in that technique detect faults in performance (Hay. where the practical limitations of some simulation models were also addressed.
Produce a schematic diagram of a menu-based analysis system for all the stages of the hierarchical technique model of Figure 6. With reference to the example of propulsive force generation in swimming (Figure 8. Even there.262 Feedback of results to improve performance not widely reported: indeed that developed by Huffman et al. Repeat exercise 4 for a technique model of a sporting activity of your choice that has a simple performance criterion. 8. 2.6 Summary In this chapter. Construct an analysis chart (similar to Figure 8. no attempt was made to ascertain whether the feedback provided by such a simulator resulted in improvements in performance. 7. 8.2. The strengths and weaknesses of the various technique assessment models and their limitations in feedback were described. for example a low take-off angle in long jump or overrotation in a high-board dive. assess which of the above three points were violated in providing information to swimming coaches about the S-shaped pull pattern based on cinematography. for example by comparing the results from a group of athletes trained on the simulator with a control group. 4.6) for the activity that you chose for exercise 3. 5.1). (1993) for the bob-sled is a rare example. The three stages of learning a sports technique were defined and the relevance of each to technique improvement was addressed. 6. consideration was given to how the results of biomechanical studies of sports techniques can be communicated and fed back to the athlete and coach to improve performance.7 Exercises 1. 3. However. Illustrate the usefulness of each of these various approaches in the context of identifying and correcting a specific technique fault in a sporting activity of your choice. The concluded with a brief coverage of the use of computer-based feed back and outlined likely developments in this mode of provision. List and briefly discuss the three points that must be satisfied for biomechanical feedback to be relevant to the sports practitioner. Which of the three phases of skill learning is most important to the . such simulators do have great potential for providing relevant feedback of sports biomechanics information. The fundamental points that must be satisfied for biomechanical fee coach and athlete to be relevant were covered. The issues that must be addressed in seeking to optimise the provision of information to the coach and athlete were considered. particularly when combined with the techniques of virtual reality.1 and section 8. List and briefly explain the various forms of technique assessment ‘model’ that can be used in conjunction with biomechanical feedback. An appreciation was provided of the important roles played by technique training and skill acquisition in the process of modifying a sports technique.
279–86.. P. Conex. 9.). pp. R. 8.J. pp. Belmont. R. 111–123. in Exercise and Sport Sciences Reviews—Volume 19 (ed. Black.B. Illustrate these points by reference to the technique fault that you used in exercise 3. England. Journal of Biomechanics..Cappozzo. Dick. Cappozzo. compare and contrast the results of Schmidt (1991) and Broker et al.A. Brooks/Cole. in Biomechanics in Sports: Proceedings of the VIIIth International Symposium of the Society of Biomechanics in Sports (eds M. K. and Marschall.J. (1989) Improving elite performance through precise biomechanical analysis. (1967) Human Performance.M.Morrison and P. Prague. London.P. Skinner. F. Broker. in future Directions in Exercise and Sport Science Research (eds J.Susanka).&C. Czech Republic.O. Schorndorf.Marchetti and V.S. CA. 227–242.A.N. Outline the points to which a coach should attend when seeking to eliminate faults in the technique of an athlete.E. M. and Sawyer.M. R. Blischke. D. After consulting the appropriate further reading..M. After consulting the appropriate further reading. and Posner. C. (b) whole or part practice? Please provide full justifications for your answers. Williams & Wilkins. Tosi). M. IL. J. and Ryan. Fitts. Rome. Champaign. (1992) Assessment of musculoskeletal disorders by locomotion analysis: a critical and epistemological historical review. in Biolocomotion: a Century of Research Using Moving Pictures (eds A.A. (1989) Beiträge zum visuomotorische Lernen im Sport (Contributions to Visual-motor Learning in Sport). (1993) Extrinsic feedback and the learning of kinetic patterns in cycling. J. Broker..Sojka. 127–169. (1989) Sports Training Principles. R.J. M.J.W. Daugs. 10. Brand. 302. Bartlett. F. Human Kinetics. (1997) Introduction to Sports Biomechanics.Holloszy). which one of each of the following pairs would you recommend in technique training: (a) massed or distributed practice.P. MD. Bartlett. (1983) Considerations on clinical gait evaluation. Dillman. Olivier. 16. 8.Landers et al. and Schmidt. Baltimore. USA. W. (1990) Javelin flight simulation—interactive software for research and coaches. R. C.M.. J. pp. E. & F. N. A. R. pp. USA.M.Nosek. London.Corbin. R. Best. R. Journal of Applied Biomechanics. USA. outline the major developments in the computerised feedback of information from sports biomechanics that you think are most likely in the next five years. A. D. 9.References 263 sports biomechanist when interacting with a coach and high standard athlete to correct a technique fault? For the specific fault that you identified in exercise 3. Promograph. 91–95. (1993) on the value of immediate and summary feedback. Gregor. R. (1991) The biomechanics of cycling.8 References . Spon. Hofmann. Gregor.
). 3– 12. 13. Sage. Rarick. 583–595. (1979) A hydrodynamic analysis of swimming propulsion. Hay.Landers et al. Addison-Wesley. (1989) Mechanical descriptors of movement and microcomputer applications: a commentary. IL. IL. Schleihauf. 223–227. Journal of Biomechanics. Q. Hatze. in Swimming III (eds J. (1993) Use of an interactive bobsled simulator in driver training. in future Directions in Exercise and Sport Science Research (eds J. and Bartlett..Bedingfield).S. 1. University Park Press. Hubbard.A. USA. Hubbard. (1993) Body roll and handpath in free style swimming: a computer simulation. Champaign. USA. J. Lapham. USA. in Enhancing Human Performance in Sport: New Concepts and Developments (eds R. 251–255. pp. A.M. 70–109. IL.G. Human Kinetics.M.R. H. 28. J.P. Huffman. and Mullineaux. Hay. 395–410. 19–32. and Andrews. (1992) Performance feedback and new advances. 9.Landers et al. 51.S. L. pp. 263–266.S. J. USA. (1980) Cognitive-motor relationships in the growing years. 238–253. G. Human Kinetics. Champaign. and Reus.Corbin. Research Quarterly. J. (1989) Rapid and accurate estimation of release conditions in the javelin throw. C.G. Baltimore. C.H. J. (1991) Motor Learning and Performance: from Principles to Practice. .). R.J.K. (1985) Running training.C. 229–237. Liu. J. M. Journal of Applied Biomechanics.A. Hay. Reading. R. 1).B. American Society of Mechanical Engineers. Journal of Applied Biomechanics. in Advances in Bio engineer ing. and Ryan.Skinner. 9. R. Schmidt. Research Quarterly for Exercise and Sport. methods and recent developments. Liu. D.W. MA. D. Journal of Biomechanics. (1993) Body roll and handpath in free style swimming: an experimental study. pp. (1977) Introduction to Motor Behaviour: a Neurophysiological Approach. H. Mathematical Biosciences. L.Corbin. Payton. Hay.G. Hatze.Christina and H. Vol. 227–237.M. M. Schmidt.. instruction on running technique.264 Feedback of results to improve performance Gregor. Journal of Sports Sciences. J.Skinner.G. MD. R. Journal of Sports Sciences. (1989) Towards a better understanding of the acquisition of skill: theoretical and practical contributions of the task approach. Human Kinetics.J.M.K.M. Petray. R. G. (1997) The effect of body roll on hand speed and hand path in front crawl swimming: a simulation study.W. and running economy in 10-year-old males.G. IL. 13. 300–315. 56. (1983) Computerised optimisation of sports motions: an overview of possibilities. USA. 53–61. USA. Q. M. New York. pp. Champaign. 26. in Future Directions in Exercise and Sport Science Research (eds J. Broker. Journal of Applied Biomechanics. 99–135. (1976) The complete optimisation of a human motion. 22. J. pp.. Champaign. and Andrews.G. R.. and Krahenbuhl. D. (1995) The use of artificial intelligence in the analysis of sports performance: a review of applications in human gait analysis and future directions for sports biomechanists. 26(suppl. M. and Alaways.W. (1993) Computer simulation in sport and industry.Terauds and E.B. Hubbard. 174–92..Eckert). Human Kinetics. C. C.
R. (1993) Extrinsic feedback and the learning of kinetic patterns in cycling. Human Kinetics. Broker. 53–61. Human Kinetics. R. New York. Journal of Applied Biomechanics. This is a rare review of the potential uses of artificial intelligence in sports biomechanics. It also presents the second example considered in this chapter comparing immediate and summary feedback. 8. 47–62. USA. Gregor. pp. Basle. Schmidt. (1989) Model technique analysis sheet for the horizontal jumps: part 1— the long jump. R. of motor skills. G. 9. 1). New Studies in Athletics. Lapham.Atha). (1987) Theoretical models and their application to aerial movement. (1980) The Learning of Motor Skills. USA. pp. 86–106. (1995) The use of artificial intelligence in the analysis of sports performance: a review of applications in human gait analysis and future directions for sports biomechanists. Yeadon. (1992) Performance feedback and new advances. 111–123. in Enhancing Human Performance in Sport: New Concepts and Developments (eds R.C. in Current Research in Sports Biomechanics (eds B.A. Hubbard.A.Van Gheluwe and J. Journal of Sports Sciences. This contains clear expositions of all issues relating to learning. IL. R. (1991) Motor Learning and Performance: from Principles to Practice. R. Champaign. This provides a good overview of the state of computer simulation modelling. Macmillan. M. 229–237. M. A. IL.Christina and H.Eckert). 13.J. and Schmidt.Further reading 265 Singer.. 3. This presents one of the two examples considered in this chapter comparing immediate and summary feedback.J. and Bartlett. J. Karger. 26(suppl.M. Gregor.N. Switzerland. J.M. Champaign. and it touches on feedback issues. This provides a good overview of the use of biomechanical feedback in improving performance. (1993) Computer simulation in sport and industry.P. M..W. Journal of Biomechanics. R.P.M. Broker.9 Further reading . and relearning. Tidow. 19–32. R. and Ryan.
93 Enoka. 49 Fitts. 26. 50. 122.M. K.L. 125 Challis.K. 80 Easterling. 6. 58.D. R. 182. 131 Cuin.V. R.Y.J. 259. J.M.P. 133 Chow. 68. S. 230 Denoth. 131 Cook. 133 Evans.P. 36 Atwater. A.E. P. J.W. 70. 78 Craton. 25 Caine.A. 129 Beaupré. J. 19 Booth.M. 108 Cunningham. S. 261 Best. 85 Connolly. T. 190. 127. D. 248. 180. 228.L. G. 183. 256.T. 126. B. 82 Bell. 43. A. 235. T. 27. D. L. B.J. D. 42. 258 Dillman. 70. N. A. 127. 5.A. 79. 127.N. 49 Alaways. 258.C. I. R. 122 Alexander. 90 Biewener.E. 28. 203. W.W. 124. 59. 134 Cavanagh. 189 Curwin. 154 Bojanic. 90 Crowninshield. T. G.R. D. R.G. 126. 261 Basmajian. 245 Donner.B. 42 Butler. 19. 31. N. J. 258 Fortney. 77. 55. 184. 89.C. 110. 124 Chan.J. 81. 88 Bober. 95 Bartlett. 124. 60 Chapman. F. 226. 181 Contini. 132 Clarke.D. 129. 161. 156.A.W. W. 28 Edington. 153. 70. 167. 36. 96 Dapena. 163.Author index Abelew. D.C. 129. 71 Berme. 15.J. 122 Foster. A. 56. 153. 51 Adams. D. 130 Bishop. K. C. 44. 193. 210. 82. V. R. 23. 211. 119. 196. 21. 239 An.D. 29.E. 189. 59 Beynnon.E. V. 260 De Luca. 150. 93 . J. N. 127. 181. T. 180 Daugs. 47 Dempster. 96 Chandler. J. A. J. 24. 161. P. 83.R. S. T. C. 163 Burr. 182 Bean. 85 Cole.H. 258. 261 Aleshinsky. 51. K.S. 133 Cappozzo.D. D. G.McN. F. D. 128.-N. M. 196 Bernstein. B. 80 Edgerton. 86. 47. R. 128. 78. 82. 93. 129 Dunning. 259 Brubaker.W. 54 Faxén. 168 Dehaven. M. D. 133 Adams. 58. 42. 111. 149–50 Berson.D. 126.R. 131.E.M. 30. 190. D. 130. 252. 159 Bunday. 122 Andriacchi. 44. K. I. R. 168 Baumann. 201–9. R. 129 Anderson. 204. 47. 113. 87. 244 Broker. G. 29 Brand.E. 53. 192 Burke. 127 Andrews. 207.D. B. 8 Binding. 244 Carter. E.A. 28 Elliott. 30.R.E. 189 Dul. 43.K.J. T.B. C.M. 89. 128. C.J. 82 Bonfield. 84 Chaffin. 209. 134 Dick. 56 Elliott. P.B. N. R. 22. 59 Best. W. 15. 134 Becker. D.-L. 45 Caldwell.H.J. J. B. B.
S.W. 181. 56. W. 28. 181. E. S.J. 207. 4. P. G.M.N. K.J. 89. A. 47. 29 Gowitzke. 30. 124. 133 HØlmich. M. 235 Higgins. D.C. 30.Y. S. 235–9. 152 Kent.A.J.H. E. 74. 196. 135–8 Jensen. 57–8. 59 Loitz. C. 29. 23.R.B.K. 24. 44.R. 37. 247 Lloyd-Smith. 133 Fukunaga. 59 Jacobson. 190. 205 Kraemer. 41 Grabiner.E. B.A. 172. 28. W. 133. P. 44 Kibler. 96–7.L. Q. 47. 23. 154 Hill. A. 223. 42.Y. R. D. J.J. I. 77. 120. R. M. 15.C.J. 245 Griffin. 210. H. 126 McDermott. 154. A.268 Author index Fowler. H.R. 97 Kunz. M.V 233–4 Hof. 99 Frank. 202–3. 126.C. 44.A. 76. 184–8. 42. 90 Incavo. 224–6 Happee. 89. 119 Lewis. 23 Gould.P. E. 28 Hanavan.K.L. 203 Leadbetter. 49 Kaufman. 150. 211 Lintner. 22 Garrett. K. 71 Komi. C. 232–3. 59. 133 Maclntyre. 92 Hay. C. D. 96. C. 19. 56. 188 Hsu. W.A.B. V.E. S. C. 159 Jelen. 21. 81 Hardt. G. T. 81 J rgensen. 132 Levinson. 30. B. 82 Frohlich. T. 75. 19. 89. 91 MacConaill. 132. W. R.B. D. 91 Jacobs. S. 258. S. 43.E. S.E. P. 23. 31. 131 Hardiker. 27. J.C. 51.N. R. K. 122 Jia. 83. 51 Harrison. 107 Gregor. H. D. 47 Liu. P. 126 Harrington. 261 Henning. S. 43 Hawkins. 156. 96 Hubbard.A. 182 Lapham. J. 130–1. 132 James. 129. 28. A. 43.J. 131 Kawakami. 131.A. 134 Kolitzus. 195. R.J. 234. 179. 96 Howell. 246. 4. A. R.K. 26. D. 27 Hunter. 27. 203. 60 Leonard. 98 Macera. 57–8. A.J. M.A. M. 124 Hatze. 150. D. 53. 227–9. 56–7 Grimston.R. 128. W. G. 181 Lindsay. 126. E. B. 195. R.I. 89.S. 162 Kane. 127 Grana. S. 129 Gracovetsky. 29 Kelso. R. 222.J. 58. D. 76. M. 234 Frazer. 157. P. 261 Laporte. 96 Kanatani-Fujimoto. S. J. R. 29 Krahenbuhl. 202 Fuglevand. Q. 128. 24.M. 27 Loitz.M. 28.D. 261 Huffman. 221. 95. 15. 192–3. 57 Karlsson. 59 Gollhofer. 125.G. 82. 119 Kannus. M. 259. 81 Frankel. 74 McGill. 81. 183. 262 Huijing. 181 Korjus. M.E. P.C.V. 173 Gottlieb. 90. T. 97 Herzog. 68 Gordon. 68.B. 121. U. 40. 209 Johnson. 74. P. L.R. T. 119.J. 42. 50. 47. 23 Lutz. 86 Luhtanen. W. 261–2 Hauser. 27. 27. 29. 127. 59 . 58. 124.S.R. 131 King. 182. 49 Greene.R. 260 Kuland.J. 77 Hawkings.L.H.J. 27. 19. 129. 193. 158 Gozna. S. 124. 60 Kim. 133 Frederick. J. 91 Jones. 223. 27 Luethi. Y. 19. 25. W.
19. H.Author index 269 McKenzie.-C. 28 Siemienski.E. M. 77. 130. 53 Marónski. 258 Sobel. M.J. 26. T. 83. 90. 246 Schmidt. R. 219 Trinkle.S. 52 Tipp. H. 77 Schleihauf. 87 Shrive. W.S. 77 Pierrynowski. 153 Stacoff. 184 Nigg. 202 SØrensen.M.N. 42. M.J.L. 81 Morrison. T. 53. S. G. M. 84. A. 99 Tutjowitsch. P. 88. M. J. 19 van den Bogert. T.T. D.L. L. 53. 49 Menard. J. 135 van Audekercke. P. 105. 92 Marone.E. 76. 107 McVicar. 115.G. 190. 222 Pinkowski. M. 134 Rarick. 54. 21. 92. A. 161. 73. 60 Miller. 95 Soong. 50.P. K. 82. 88 Vaughan. C. 181 Meyers.A. 70. 8. R. J. 122. Y.C.H. 182 Mullineaux 183.H. 87. 134 Morriss.F. T. B. C. 85. 134 Puddu.M.G. 255 Rasch.E. B. 202. 22. 51 Moffroid.T. 19. 196 Parry.M. L. 55. 246 Pecina. 86. 86 Prilutsky. 131 Pike. P. 57 Mero.K. 79. R. 191–2. 6. 71.R. 90 Payton. 195 Viitasalo. M. W. C. D. 131 O’Neill. 36. 74. 115. G.E.M. 85. A. K.F. S. W.W. N. 90 Schaff. J.H. W.N.H. J. M. 84 Mitchell. 245. 234 Norman. 74 Stüssi. 181 Paulos.G. 4 Moore. 90 Polich. 219 Ulbrichová. 107 Torg. 19 Martin. N. 53. L. 51 Sage.I. 205 . R.F. 257. 131.D. 87. C. A. 82. J.A. 28. 71. 50 Marzo. 163 Red. 86. R. 258 Sanderson. N. 258 Pratt. 181 Nirschl. 91. C. 56. J. 55 Tucker. 95. 59 Mallon. M. 130 Milner. 205 Reid.N. 37.J. 106.J. J. 82 Pedotti. G. R. J. A J. B. J. T. 96 Steindler. 78. 67. 95 Nordin. M.A. J.G. 90. 4. A. 152. 68. 126 Singer. J. 47. 210–21 Martens. 90 Pope. 82. G.H. 81 Swan. 90 McLaughlin. H. 124. 126 Petray. 184 Reilly. 60 Thompson. 69. 81. 192–3. 57. 90 Posner. 87. 75 Orava.J. 44. 221 Troup.A. 76–7. 29. C. 44 Özkaya. 47. 89 Townend. 222 van Ingen Schenau. 153 Ranu. 211 Müller. 86 Stanish. 130 McLellan. 47. A. 59. 92. D.W. 76. 84 McMahon.B. 133 Nubar. 79. G. A. 196. 127 Segesser. 125 Van Gheluwe. J. 24 van Mechelen. 96. P. E. J. 19. 156. R. 8.F. N. 59. 98 Renström. 21. 55. K. F. M. 82. 89. B. 258 Schultz. 15 Pandy. 70. 49 Putnam. 23.J. W. 19.C.D. 190.B.W 202 Taunton. 54. 83. 20 Stucke. 158 Milsum.G.S.L. W.R. 194 Misevich. 260 Pförringer. 42. 21.W. J. 3. 210. 45 Rimmer. 84. D. 74. C.A. 15.
L. 86 Winters. A. 229–32. 37. B. 81 Williams.J. 74.G. A. 191. 49 Wilkinson. 196 Zatsiorsky. 121.R. 29. T. V. 122. 130. R. 261 Yeo. 122 Zernicke.-Y. 107 Wickiewicz. W. 56 Watson. 126 Yoshihuku. 73. 70.R.G. J.H. R. 28.P. 71.M.M. 75. 188 Watkins.270 Author index Vincent. 152 Williams. K. 37 Zogaib.L. 134 Woo. V. 205 . 222–3. 71. F. 120. W. Y. M. 119. C. 172. 29.J. 106. J. 47. 138 Zetterberg. 235 Zajac.F. 26 Yeadon. S. 69. 23.E. 193 Wismans. 124.J. 173. 105.
protector 49. 18 ankle:braces 90. 86 compliance: surfaces 69. 159 acute injuries 36. 42. 104 condition problem 202 connective tissue. atrophy 27. 43 collateral ligaments 97 combination-lasted shoes 80 comminuted fractures 41 compact bone 19 compartment syndromes 43–4. 17. injuries 37–42. 86 action phase 157. 56–7 American football 53. age and sex variations 27–8. 12. tendonitis 82. spinal injuries 54 bicipital tenosynovitis 96 biomechanical optimisation 178–200 board-lasted shoes 80 bone 15–20. 104. 19. non-homogeneity 15. 10. injuries 42 cast in situ elastomers 105 central nervous system (CNS) 150–2 cervical spine injuries 54–5 chondroitin 20 closed kinetic chains 173–4 closed-cell polymeric foam 78 closed-loop control 150–1 collagen 25. fractures 37–8. 74–5. 41. knee injuries 47. 19. 70–1. 28. injuries 49–50. 27 collagen fibres 20. bone 17. 107. 89 analysis charts 251–2. damage 75. mineral content 29. 251. 76. 42 Artificial Athlete Berlin 71 Artificial Athlete Stuttgart 71. 75. 53. 80. bone 19. bone 19. tendon 27 compression 6–8. 17. exercise effects 29 .Subject index α-γ coactivation 151–2 acceleration path maximisation 156 Achilles tendon 76. 72 artificial surfaces 68. 29. 83 carbon fibre-reinforced composites 5 cartilage 20–1. 222 anisotropy 15. 172 ballistic stretching 59 basketball 49 bending 8. 167. training effects 28–9 bony alignment 57–8 bound-crumb polymeric surfaces 106 boxing 54 breaststroker’s knee 98–9 brittle materials 13 brittleness. 43 aerial movement 222–4 age 27–8. 254 angular impulse-momentum equation 213 angular momentum 153 angular momentum conservation 219–20. 261–2 computer-based feedback 260–2 computerised three-dimensional image-based motion analysis 248 concrete 70. 81 back injuries 53–6 back-arching activities 55 badminton 88. 76 asphalt 70. exercise effects 29. 75. immobilisation 27. 28. density 28. 248. 70. 89–90 ballistic movement 157–9. 74. 75. 106. 253. 28 bulk mechanical properties 6 bursitis 49 butterfly fractures 40 cancellous bone 15–16. forces 134. 81 area moment of inertia 10 arthritis 28 articular cartilage 20–1. cartilage 20. 75. 98. 104 autonomous learning stage 257 avulsion fractures 28. 40. injuries 49. 254. 69. stresses 10. 26. spinal injuries 54 compression set 78 compression test 14 computed torque 232–3 computer modelling see mathematical models computer simulation 191–2.
15. 128–9 crack prevention 13 crack propagation 17. hand and wrist 51. 85 energy-to-failure 29 equality constraint 125 equipment 5. 28 cost functions 125. 29. stretchshortening cycle 23. 88. 53 contractility. 108 cricket 56. 126. 183 cortical bone 15. 73 ductile materials 13 ductility 12 dynamic balance movement 167 dynamic loading 19 dynamic optimisation 193. 82 distributed practice 257–8 disuse 27 diving 256 downhill running 76 drop tests 71. microfractures 75. 17. knee 47. 67–108 expert systems 261 falling techniques 93 fatigue failure 14 fatigue limit 14 feedback 150. 244–65 fibre-reinforced composites 5 fibre-reinforced polymers 5 fitness 4. bone 19. ligaments 24. age and sex variations 28. 58–60 flight phase 202 follow-through 160 foot: descent 160. 211 elastic energy 27. types 37–40 free-body diagrams 110.272 Subject index constrained optimisation 193 contact sports 3. 92–3. 196. 108 friction syndrome 47 . strike 159. 67–8. ankle 49. 159 correlation method 181. cartilage 20. 168 élite performer template 180–1 EMG see electromyographs endurance training 29 energy conservation 85 energy loss: assessment 73–4. plastic deformation 12 energy minimisation 154 energy return 79. 28. 74. 83–4 force–velocity curve 23. shoulder 53. surfaces 68–9. 94 cross-sectional analysis 181–2 cruciate ligament 47. 127. 51. 259 cylinders 10–11 deflection-time methods 71 delayed-onset muscle soreness (DOMS) 43 deltoid ligament 98 demonstrations 248 deterministic modelling see mathematical models diagrammatic models 250–1 diaphyseal impaction fractures 37 discus throwing 210–21 distance running 60. 19. 95 electrogoniometric records 163 electromyographs (EMG) 133–4. 161–2 footwear 49. 205 elbow injuries 51–2. injuries 49–50. 118 force locking 68 force reduction 70 force-deformation curve 73 force-extension curve 12 force-time curves 29. tendon 26 elastic strain energy 12–13 elasticity: cartilage 20. 115. 24 force/vector polygon 111. elbow injuries 51. 19. 38 creep 14. 16. 81. 163. 111. storage 158. tendon 27 elastomers 106. muscles 21–2 contrast method 182 cool-down 28 coordinated movement 149–56. 97 cyclic bending strain 29 cyclic loading 36–7 cycling 235. 21. muscles 21–2. 202. 18–19. 112 forefoot running 83 forward dynamics 131–2 forward optimisation 192 forward swing 160 Fosbury flop 98 fracture toughness 13 fractures 17. 117 friction: footwear 82. 167. 76–87 footwear-surface interface 67. 90 force enhancement 24 force equilibrium 110. 99. 91. 76. 112. 24 elastic modulus 11–12.
252 high jump 190. knee injuries 47. 13 global optima 193–4 golfer’s elbow 52 Golgitendon organ: facilitation 158. 96 length–tension relationship 158 ligaments 24–6. 47–9 knee braces 90 knee injuries: breaststroker’s knee 98–9. 248. body behaviour 36–66. team sports 97. 75 . 248 hamstring strains 59. age variations 28. 89–90. 221 hip joint 45. 56. forces 134. 15. 258. 69–70 head injuries 53–6. 98. variations 27–8 genetic factors 4. bone 18–20. 124–5 individual sports 3 inequality constraint 126 inertia model 229–32 inertial coupling 121 inference engine 261 inserts 81 insole 80 insole board 80 International Amateur Athletics Federation 70 inverse dynamic optimisation 130 inverse dynamics 109–10. exercise effects 29. computer simulation 261.Subject index 273 gender: injury effects 56–7. 45–56 joint reaction forces and moments 116–18. 232. 119–24 jumper’s knee 49 jumping 97–8 junction strength 29 Kane’s method 119 kinesiological analysis 162–8 kinetic chain 154 knee 20. cartilage 20–1. skiing injuries 91 limitation of excitation of muscles principle 154 linked segment models 222–32 live demonstrations 248 load: assessment 71–3. 97 hammer throwing 210–21. 233 inverse optimisation 125–32 inverse static optimisation 130 javelin 95. 82 haemarthrosis 42. 88–9. 27 hysteresis loop 12 iliotibial band syndrome 59. injury effects 56–7 guided movement 167 gum shields 88 gymnastics 55. 82. definition 6. 97 hamstrings 45 hand injuries 50–1 hardness 14. models 227. injuries 42–3. shoulder injuries 53. footwear 81. magnitude 40. weight-lifting 99 knee lift 92 lacrosse 88 Lagrange Formalism 119 landing techniques 97–8 lateral epicondylitis (tennis elbow) 51. 86 immobilisation 27 impact attenuation 70. 228. 210. 192–3. ankle injuries 49. 86 heel–toe running 83–4 hierarchical models 184–9. 92–3 headgear 88 heel counter 80. immobilisation 27. material response 6–15. 251. 97 horizontal load assessment 73 hurdling 98 hyaline cartilage 20 hypertrophy 29 hysteresis 13. 45. rate 40–1. characteristics 4. 56–8 glass fibre-reinforced composites 5 glass transition temperature 5. 201–10. throw 160–1 javelin thrower’s elbow 52 joint injuries 42–4. inhibition 159 graphical models 250–1 grass surfaces 70 growth. 12. skiing 91. calculation 109–48. 46 hockey 87. 82–5 impact shock 80 impact tests 13 impingement syndrome 96 impulse generation-absorption 155 impulse–momentum equation 155 impulse-momentum relationship 186 indeterminacy problem 115–16. ligaments 25–6. 86 impact force 75.
92–3 massed practice 257–8 mathematical models 189–96. shoulder 53. strength imbalances 59 muscle-tendon unit 43–4. hammer throwing 213–18. 87 pes planus 58 phase analysis 154. 58. 155–6 particular principles 153 passive movement 167 patellar tendinitis 49 patellofemoral joint 45 patellofemoral pain syndrome 47. 118 moment of inertia 10. 105 porosity. 45 myositis ossificans 43 natural surfaces 70 neck injuries 53–6. 182 low-back pain 55. 89–90. 156–62 phasic discharge 158 planar joint reaction forces and moments 116–18. impact 82. 88–9 negative transfer 255–6 net reaction forces and moments 116 neutral axis 8 Newton’s second law for rotational motion 213 non-contact sports 3 non-homogeneity 15. throwing 95. fatigue failure 14. 58 pedicle sclerosis 93 pelvis 45 performance criterion 179. shin splints 44. 86 minimisation of inertia 155 minimum energy principle 194 minimum task complexity 154–5 moment equilibrium 116. stress fractures 37. 192–5. 90 oscillating movement 167 osteitis pubis 45 osteoarthritis 42 osteoclasts 82 osteons 15. 119–24 plantar fasciitis 50. 99 open kinetic chains 173 open-loop control 150–1 optimal control theory 193. 185 performance enhancement 147–265 peripheral nervous system (PNS) 150–2 peritendinitis 49 peritendon 80 peroneal retinaculum 91 pes cavus 58. tennis elbow 51. 43. 232–3. 28 outsoles 80 overarm throwing 40 overtraining 59 overuse injuries 14. 83. elastic modulus 12 polyurethane foam 78–9 polyurethane rubbers 80. 13 plastic strain energy 12 plasticity 12–13 pole vault 98 polymers 5. 85. models 232–40. soft tissue 42. foot 50. javelin throwing 205 orthotic devices 81. computer-based feedback 261–2. 82–3. 96. 58 plastic deformation 12. 253 longitudinal analysis 181. pes planus 58. activation 22. 18 non-support phase 160 objective function 125 oblique fractures 40 oblique transverse fractures 40 Olympic lift 92. 133 mechanical stiffness 22–3 medial epicondylitis (golfer’s elbow) 52 medial tibial syndrome 44 meniscus tears 47 mental practice 258 menu-based systems 251 mid-support 159 midsoles 78–9. 201–43 maximum force 22 maximum voluntary contraction (MVC) 30. 202 optimisation 189. knee injuries 47. surfaces 108 . exercise effects 29. age differences 57. 41 motor learning 258–60 motor learning stage 256–7 motor unit recruitment 22 motor unit stimulation rate 22 muscle 21–4.274 Subject index local optima 193–4 long distance runners 28–9 long jump 238. 17. 201–2. 36–7. 30. 57. tendons 60. upper extremity 89 parallel representations 248 part practice 258 partial generality principles 153.
footwear 76–87. knee injuries 47. 76 slip-lasted shoes 80 soccer 49. spondylolysis 56. knee injuries 47. 209–10. 219–20. tendon 26 strain 6–11 strain energy 12–13 strength training 60 strength-to-weight ratio. 106. tackling 97 soft tissue: injuries 42–4. tendons soft-saturation 126 sorbothane 81 specific tension 22 spikes 68. gum shields 88. 81. shoulder injuries 53. 29. 222. 51. tendon 27 resistance strength training 59–60 rigid body model 190. stretching 59. validation 233 skeletal muscle. 232 rolling resistance 108 rotation-causing activities 55 rugby 47. 77. javelin throwing 204–5. sex differences 57. gender differences 56. 41.Subject index 275 positive transfer 256 posterior tibial tendinitis 86 pre-stretch 154 preparation phase 157. 159 reduction method 124 redundancy problem see indeterminacy problem reflex potentiation. hammer throwing 213–18. 89. 213–18 sequential action of muscles 155. spinal injuries 54 shin splints 44. see also cartilage. 201. ligaments. surfaces 76. 89–90 stability 156 static force 116 static optimisation 193. 12. 202–3 static stretching 59 statistical modelling 181–9 stiffness 11. 95. 261–2. 84–5 shoes see footwear shot-put 95 shoulder injuries 53. 158 principal stresses 8. 58. 190–2. 82–3 shock absorbency 70. evaluation 190. 75–6. 49 stress fractures 37. bone 16 stress 6–11 stress concentration 15. modelling 232–40 ski jumps 222. muscle 22–3. 248. 254. 10. traction force 68 segmentation 157 semi-quantitative analysis 157 sensitivity analysis 205–8. 29. surfaces 69. stretch-shortening cycle 23 relearning techniques 255–7 release bindings 91 release parameters 202 resilience 13. 159 serial recordings 248 servomechanism 151 shear 6–8. 26 stretch-induced injuries 44 . foot 50. 97 running 37. 30 stress resistance 16 stress-strain curve 12. boots 81. 83. throwing 95 simulation 189. 91 sliding 74. 158. 92–3 sprung wood floors 105 squash 88. impact 82. tackling 93. 30. phase analysis 159–60. 10 pronation 85–7 proprioceptive feedback 256 proprioceptive stretching 59 protective equipment 87–9 PVC 106 qualitative analysis 156 quantitative analysis 156–7 quasi-rigid body model 210–21 racket sports 95–6 rackets 89 rate-coding 22 rearfoot control 85–7. 107. team sports 97 stress relaxation 15. 221. bony alignment 58. 232–3 skiing 40. 69. swimming 96–7. 69 spinal injury. 70. muscle. surfaces 104. technique 98. 60. bone 19. 41–2. ligaments 25. ankle injuries 49. head injuries 54. weight training 92 spiral fractures 38–9 spondylolisthesis 93 spondylolysis 56. 90 rearfoot stability 80 rearfoot strikers 83 rebound resilience 69 recovery phase 157. 59. 30.
194 stretching 30. cartilage 20. spiral fractures 38 toughness 13 trabeculae 16–17 traction. bone 19. 10. 95. injury effects 58 weight-lifting 92. 88 whole practice 258 wobbling mass model 115 wobbling mode 222 wood floors 105 work–energy relationship 156.276 Subject index stretch-shortening cycle 23–4. age effects 28. 26. 76 tennis elbow 51. status 4. players 29. spinal injuries 55. injuries 44. spinal injuries 54. assessment models 247–54. injury effects 67–108. hysteresis 13. 97 technique 4. 97 take-off 160 team sports 3. see also discus throwing. technique effects 92–3 tuned tracks 107–8 twisting see torsion twisting mode 222 ultimate compressive stress 21 ultimate strength 19. training 254–8 temporal analysis 156–62 tendinitis 49. 98–9. 51. 104 training 28–30. 40. 186 wrist extensor injuries 96 wrist injuries 50–1 . errors 60. 60 wedges 78–9 weight. hammer throwing. 12. 154–5 unweighting 97 uphill running 76. 29 ultimate stress 27 ultimate tensile strain. 24. 92. musculoskeletal injury 91–9. bone 19. bones 28. 96. 158. models 235 volleyball spike 160 warm-up 28. 28 unconstrained optimisation 193 universal principles 153. 95–6. 245–7 synovial membrane 42 synthetic fibre textile surfaces 106 synthetic turf 107 tackling 93. 53. 209 triceps brachii 236–7 triple jump 98 tropocollagen 25 trunk injuries. 58. 89–90. 96 tension 6–8. bone 28 ultimate tensile strength 12 ultimate tensile stress 12. overuse injuries 60. bone 18. 15. energy loss assessment 73. 154. 105. ballistic movements 157–9. 55 textbook technique 249 theory-based statistical modelling 184–6 three-dimensional stresses 8 thrower’s elbow 52 throwing sports 82. 67–76 sustained force movement 167 swimmer’s shoulder 96 swimming 59. creep 13. 93–4. 58–60 transverse fractures 37–8 traumatic fractures 37 traumatic injuries 36. javelin thrust phase 202 tibia decelerations 84 tibial stress injury 47 tibiofemoral joint 45 tissue characteristics 4 tonic response 158 torsion 8. 30–1. exercise effects 29. 99 tendon force 124 tendonitis 82 tendons 26–7. 82 uppers 77 vaulting pole 5 verbal–cognitive learning stage 256 vertical load assessment 71–3 viscoelasticity 15. stress-strain behaviour 12 tennis 58–9. injuries 51. 95. 59. 15. 59 structural analysis 152–4 studs 81 support phase 159–60 supracondylar fracture 51 surfaces 5. surfaces 68–9. 10. 41. 99 weight-loading 55 whiplash 53. 53. surfaces 74. 135–8 trial and error approach 179–81. 75. 96–7.