The VMO:VL activation ratio while squatting with hip adduction is influenced by the choice of recording electrode

Concomitant hip adduction during squatting has long been advocated as a rehabilitative method to preferentially activate the VMO in persons with patellofemoral pain. This practice however has been based on research using surface electrodes which are prone to crosstalk from neighboring muscles (i.e., adductor magnus). This study sought to determine whether activation levels of the VMO relative to the VL while squatting with hip adduction would differ based on the choice of recording electrode. Ten healthy subjects performed a maneuver with hip adduction and without hip adduction. The mean VMO and VL activation levels were recorded simultaneously with surface and indwelling fine-wire electrodes. For both recording electrodes, the VMO and VL activity increased significantly with the addition of hip adduction (p < 0.05). However, the increase in VMO activation was more pronounced with surface electrodes, resulting in a significantly higher VMO:VL ratio with the incorporation of hip adduction compared to without hip adduction (p < 0.05). No difference in the VMO:VL ratio was observed between the two squat conditions for the fine-wire electrodes (p > 0.05). Our findings suggest that the VMO:VL activation ratio when squatting with hip adduction is influenced by electrode choice.