Electromyographic analysis of the squat performed in self-selected lower extremity neutral rotation and 30 degrees of lower extremity turn-out from the self-selected neutral position

Little research is available on the muscle activity patterns of the lower extremity muscles during dynamic closed chain squatting activities. The purpose of this study was to examine the effect of lower extremity position during an Olympic squat on the muscle activity patterns of the vastus medialis, vastus lateralis, semimembranosus/semitendinosus, and biceps femoris. Twenty-five healthy, untrained subjects, 18-35 years old, were randomly assigned initial squatting positions of either self-selected neutral or 30 degrees of lower extremity turn-out from the self-selected neutral position. Surface electromyography and motion analysis data were collected simultaneously in 10 degrees intervals and analyzed from 10-60 degrees of knee flexion in both the ascending and descending phases of the squat. A four-way analysis of variance indicated that the main effects of lower extremity position and the interaction of extremity position and knee joint angles were not found to cause significant changes in muscle activity patterns. Significant changes in muscle activity did occur with changes in knee flexion angles in the vastus medialis and vastus lateralis but not in the semimembranosus/semitendinosus or biceps femoris.