Electromyographic analysis of exercises proposed for differential activation of medial and lateral quadriceps femoris muscle components

Background and Purpose. The purpose of this study was to determine whether active exercises combining hip adduction with knee extension activate medial components of the quadriceps femoris muscle (QF) more than does knee extension alone. Subjects. Twelve healthy adults (6 men, 6 women), aged 20 to 36 years (X̄=24. 8, SD=5.8), participated in the study. Methods. The subjects performed quadriceps femoris setting (QS), straight leg raising (SLR), straight leg raising with the hip laterally rotated (SLR/LR), and straight leg raising combined with isometric hip adduction (SLR/ADD). Electromyographic (EMG) activity was recorded from the oblique (VMO) and longitudinal (VML) portions of the vastus medialis, vastus lateralis (VL), and rectus femoris muscles. Results. Comparison of normalized mean EMG magnitudes revealed that the single-joint QF components (VMO, VML, and VL) demonstrated significantly greater activity during QS than during any of the three SLR variations and that SLR/LR and SLR/ADD did not elicit greater relative activity of medial QF components than did QS or SLR. Conclusion and Discussion. These findings do not support the notion that concurrent use of the hip adductors during knee extensor exercises results in preferential strengthening of the VMO.