Influence of the force applied and its period of application on the outcome of the flexion test of the distal forelimb of the horse
The influence of the force applied and its period of application on the outcome of the flexion test of the distal forelimb was investigated in a group of eight sound horses. The degree of lameness after the flexion test was scored by a standard clinical classification, and by measuring the angle of maximum fetlock extension by means of the infrared light-based MacReflex gait analysis system. There was a good correlation between the clinical score and this electronically recorded kinematic parameter (r = 0.96). Both the force applied and the period of application affected the outcome of the test. Increasing the force applied by 25 per cent led to three horses being judged positive, instead of two when the normal force was applied. Doubling the time to 120 seconds resulted in four horses rather than two being classified as lame after the test. Reducing the force to 75 per cent or the time to 30 seconds resulted in all the horses being classified as sound. A flexion test lasting five minutes, either at 100 per cent force or at 75 per cent, classified six of the eight horses as lame. It is concluded that the flexion test should be defined more precisely in terms of these two factors in order to make its results more consistent and hence more useful.
Proximal hindlimb flexion in the horse: effect on movement symmetry and implications for defining soundness.
REASONS FOR PERFORMING THE STUDY
Flexion tests are a common tool during the prepurchase and clinical lameness examination, yet studies quantifying the effect of flexion, apart from distal forelimb flexion in sound horses, are sparse.


OBJECTIVES
To investigate the effect of proximal hindlimb flexion on perceivable and measurable changes in movement symmetry in horses with objective movement symmetry falling within the margins of 'sound'.


METHODS
Thirteen horses, selected based on objective movement symmetry, were instrumented with inertial sensors on left and right tuber coxae and over the os sacrum. Vertical movement symmetry was quantified at trot before and after proximal hindlimb flexion, with a repeat of flexion after 5 min. Video recordings of the horses were assessed visually.


RESULTS
Proximal hindlimb flexion introduced additive changes in movement symmetry to the individual baseline movement, with a tendency towards smaller effects with increasing stride number. The main systematic effect was a decrease in upward movement of the os sacrum following mid-stance of the flexed limb and an increase in upward movement following mid-stance of the nonflexed limb, also manifesting in a 'hip hike' of the flexed limb; these findings reflected increased movement asymmetry following flexion. Depending on individual baseline asymmetry, flexion can also increase movement symmetry.


CONCLUSIONS
Proximal hindlimb flexion can exacerbate subtle asymmetry when performed carefully. Variation in measured symmetry following flexion within and between horses showed that the individual response to flexion is highly variable.


POTENTIAL RELEVANCE
Proximal hindlimb flexion may elevate the asymmetry of a slightly lame limb above the threshold for visibility, thus assisting in the clinical gait examination. Further work is needed to examine the causes for a positive response to flexion and possible differences between sound and lame horses as well as horses of different athletic disciplines.
Representation of systems disturbed by wide band noise
In this paper, a method of handling and working with wide band noise is developed. We represent wide band noise as a distributed delay of white noise and use it to reduce a nonlinear system disturbed by wide band noise to a nonlinear system disturbed by white noise. An application of this reduction to a nonlinear filtering problem under a wide band noise disturbance is discussed.