anatomical cadaver studies have shown that vastus medialis oblique ( vmo ) fibers originate 
 from the distal part of the adductor magnus . thus , vmo fibers provide stability during the 
 contraction that occurs in hip adduction1 . hip adduction also stretches the vmo fibers , adjusting the length and tension properties of 
 the muscle and increasing the contraction force2 . based on anatomical analyses , previous research has shown that hip 
 adductor contraction during squat exercises results in selective strengthening of the 
 vmo3 . another study reported that the 
 hip adductor muscle is connected to the internal abdominal muscle through the iliacus , psoas 
 major , and quadratus lumborum muscles4 . kim and yoo5 reported that the muscle 
 activities of the external oblique , internal oblique , and l5 paraspinal muscles increased 
 during hip adduction using a visual feedback device . hip adductor muscle contraction also 
 synergistically facilitates the pelvic floor muscle activity that occurs with the 
 contraction of the abdominal muscle6 . therefore , many clinicians have used various hip adduction exercises for low back pain , or 
 patellofemoral pain or pelvic muscle weakness patients1 , 5 , 6 . the selection of the exercise load is a very important factor in 
 the effectiveness of the exercise3 . therefore , in the present study , 
 using regression analysis , we determined the optimal and maximal loads during hip adduction 
 exercise by asymptomatic subjects . the purpose of this study was to provide data for 
 decision making regarding the optimal and maximal hip adduction loads for clinical and 
 fitness purposes , respectively . forty - eight ( 24 males , 24 females ) asymptomatic subjects with no known surgical , 
 musculoskeletal , or neurological history of any pathological condition in the lower 
 extremities participated in this study . the mean age of the participants was 24.3  
 4.4  years , their mean height was 169.5  8.4  cm , and their mean weight was 61.2  12.7  kg . this study was approved by the inje university faculty of health science human ethics 
 committee , and all subjects provided their written informed consent to participation before 
 commencing the study . subjects were instructed to bend their knees to 45 in a 
 height - adjustable chair and adduct their knees to their hip . the optimal hip adduction load was defined as sustainable load 
 holding for 20  s in isometric hip adduction isometric exercise . the maximal hip adduction 
 load was defined as sustainable load holding for 3  s with maximal effort hip adduction . the 
 hip adduction load was measured by powertrack ii ( jtech medical , salt lake city , ut , usa ) . hip adduction load measures were performed using an air cushion with the powertrack ii 
 placed between the medial joint lines of the knees . the individual optimal and maximal 
 hip adduction load data were collected from five repeated tests . a resting time of 3  min was 
 given between each test to prevent muscle fatigue . stepwise multiple regression analysis was 
 used to determine the optimal and maximal loads during the hip adduction exercise . a 
 stepwise multiple regression analysis was performed using gender , body weight and height 
 variables to identify the most informative variables for predicting the optimal and maximal 
 loads during the hip adduction exercise . the coefficients for the regression analysis and 
 the regression model for the optimal and maximal loads during the hip adduction exercise 
 were determined . to control for the gender , body weight , and height variables , stepwise multiple regression 
 was performed for the optimal and maximal hip adduction loads . the regression model for 
 optimal hip adduction load ( kg ) was : 34.3 + 0.4  weight  0.27  height ( r= 
 0.77 , p<0.05 ) ; and the regression model for maximal hip adduction load ( kg ) was : 39.5 + 
 0.5  weight  0.3  height ( r=0 0.75 , p<0.05 ) . this study measured the optimal and maximal loads during hip adduction exercise in 
 asymptomatic subjects . the most informative variables for predicting the optimal and maximal 
 loads during the hip adduction exercise were determined on the basis of statistical 
 regression . the results show that weight and height were the most informative variables for 
 both optimal and maximal hip adduction loads . using information from these models can aid in 
 deciding the optimal and maximal hip adduction loads for clinical and fitness purposes , 
 respectively . the selection of the exercise load is a very important factor for effective 
 exercise . a previous study investigated the influence of a resistive band on the muscles 
 with leg adduction performed in a variety of positions7 . core stability of the trunk can be viewed 
 as a box , with , the diaphragm as the roof and the pelvic floor and hip muscles as the 
 bottom8 . the abdominals comprise the 
 anterior part of the box and the paraspinals and gluteals the posterior part8 . this co - activation of the hip adductor , 
 pelvic floor , and internal abdominal muscles is necessary for the occurrence of 
 intra - abdominal pressure9 . thus , the optimal hip adduction load model can be used to 
 strengthen the hip adductor muscles or enhance core stability in the clinical setting . although the independent variables of this study used simple general characteristics , the 
 regression coefficients of r - squared over 0.7 indicate highly reliability in predicting the 
 dependent variables . the variables selected by regression analysis in this study were weight 
 and height , which have the advantage of being measured easily in the clinic by physical 
 therapists . therefore , our study results can help with the selection of the ideal hip 
 adduction loads in clinical situations .