7. Frontal Plane Knee Loading during Bodyweight Squat Performance: Effects of Stance Width and Foot Rotation

Abstract

The bodyweight squat is routinely used for conditioning of the knee musculature. In the performance of this exercise, modifications in the initial standing position may result in altered frontal plane kneel loading, and hence may potentially be used for targeted exercise prescription. The purpose of this study is to quantify the frontal plane mechanical loading on the knee joint whilst performing the bodyweight squat exercise, and to examine the effects of varying stance width and foot rotation angle. Twenty-four participants (14 males) performed 4 randomized sets of 8 repetitions of the body weight resistant squat exercise in the following conditions: 1) Shoulder width (SW) stance with parallel feet; 2) SW stance with feet externally rotated 30°; 3) 140% SW stance with parallel feet, and; 4) 140% SW stance with the feet externally rotated by 30°. The adduction/abduction knee joint moment experienced across conditions was calculated using inverse dynamics procedures. Moment waveforms were subjected to Principal Component (PC) analysis, with 3 PC’s retained based on a 90% trace criteria. Following, a 1-way repeated measures ANOVA and pair wise comparisons were used to discern differences between conditions. Omnibus test results indicate significant differences across conditions for PC1 and PC2 (p<0.01), Post hoc comparisons and waveform interpretation of PC1 extreme scores showed that the magnitude of the adduction moment was higher throughout the movement in the foot rotated conditions vs. the parallel feet conditions in both stance widths (mean Z scores .69 & .65 vs. -.88 & -.45, p<0.01, respectively). For PC2, significant differences were found between the 2 parallel feet conditions and the 2 foot rotated conditions, as well as between the foot conditions in the wide stance squats. PC2 differences were interpreted as phase shift operators. We found that modification of foot rotation slightly alters the magnitude and timing of knee adduction moment component during performance of the body weight squat. The observed magnitude differences are presumably a consequence of alteration in the location of the point of application of the ground reaction force during the initial standing posture. The findings may assist clinicians in exercise prescription decision making.