Fifteen female 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 23.67±3.48 years, their mean height was 162.33±4.85 cm, and their mean
weight was 52.93±5.20 kg. The electrical activity of the VMO and VL was recorded using surface EMG electrodes(Biopac System Inc. Santa Barbara, CA. USA). Prior to data analysis, all results were normalized by calculating them as a percentage of their maximal voluntary contraction (%MVC). Subjects were instructed to bend their knees to 45° and hip adduct their knees together. Subjects performed conventional squats and squat with various hip adduction loads (maximum, 80% load, and 40% load). Squat exercises were executed in the following sequence. The conventional
squat exercise was performed by descending to 45° knee flexion, holding for 6 s, and ascending to the initial position. Squat exercises with various hip adduction loads were performed by compressing a biofeedback air cushion placed between the medial joint lines of the knees. Subjects inserted the air cushion between their knees and squeezed it at maximum effort for 6 seconds, and this sustainable status was defined as the maximal hip adduction. Maximal,80%, and 40% hip adduction load squat exercises were performed by descending to 45° knee flexion and holding for 6 seconds. The data were analyzed using SPSS version 18.0 (Chicago, IL, USA) to examine the significance of differences in activation of the VMO and VL muscles among the
squat exercises. A one-way repeated measures ANOVA was initially performed to determine significant differences in the activity of each muscle during the exercises. Bonferroni’s correction was performed post hoc to assess differences among various hip adductions loads. A value of p