Hip Adduction Does not Affect VMO EMG Amplitude or VMO:VL Ratios during a Dynamic Squat Exercise

Context: Clinicians commonly attempt to facilitate vastus medialis oblique (VMO) activity by instructing patients to squeeze a ball between their knees during squatting exercises. Objective: To determine whether VMO activation amplitude and the VMO to vastus lateralis (VL) activation ratio (VMO:VL) were altered when performing active hip adduction during a dynamic squat exercise. Design: Single test session. Participants: Fifteen healthy subjects, with no history of knee pain, volunteered for this study. Intervention: Surface EMG of the VMO, VL, and hip adductor (ADD) muscles were recorded while subjects performed 10 consecutive squats against their body weight through a range of 0° to 90° of knee flexion. Subjects performed the squat exercises during two different conditions: (1) active hip adduction and (2) no hip adduction. Main Outcome Measures: Average VMO EMG amplitude and VMO:VL ratio were determined during the knee flexion (0° to 90°) and knee extension (90° to 0°) phases of the squat exercise. Results: Active hip adduction did not significantly change VMO amplitude or VMO:VL ratio during the knee flexion or knee extension phases of the dynamic squat exercise. Conclusions: Based on these results, we conclude that VMO amplitude and the VMO: VL ratio are not influenced by performing active hip adduction during a dynamic squat exercise in healthy subjects.