Medial and lateral quadriceps muscle activity during weight-bearing knee extension exercise

The purpose of this study was to determine the effect of weight-bearing terminal knee extension (WBKE) on normalized mean electromyographic (EMG) activity of the vastus medialis oblique (VMO) and vastus lateralis (VL) and the VMO/VL ratio. Sixteen subjects with no history of knee dysfunction participated. Surface EMG data were recorded from the VMO and VL of subjects' test legs as they performed the WBKE exercise under four conditions, three involving elastic resistance and one involving no elastic resistance. EMG data were normalized relative to a maximal isometric quadriceps contraction, and overall mean VMO and VL activity and the VMO/VL ratio were determined for all conditions. The three conditions utilizing elastic resistance showed higher mean VMO and VL activity than the no-resistance condition. The VMO/VL ratio was not significantly altered during any exercise condition as compared to maximal quadriceps setting exercise. WBKE against elastic resistance was superior to the same exercise without resistance for generating mean VMO and VL activity. Performance of the WBKE, regardless of the position of lower extremity rotation, does not selectively activate the VMO apart from, or to a greater degree than, the VL.