Objective: We measured the surface electromyographic activities of vastus medialis obliquus and vastus lateralis in 16 subjects with patellofemoral joint pain syndrome.
Design: Each subject performed bilateral static knee extension exercises at 60% of his or her maximal voluntary effort under different combinations of hip rotation (30 degrees of medial rotation, neutral, 45 degrees of lateral rotation) and knee flexion (20 and 40 degrees) in a standing position. The ratio of surface-integrated electromyographic signals of vastus medialis obliquus over vastus lateralis was calculated for each of the six conditions. Because of significant interaction of hip rotation and knee flexion in the two-way analysis of variance, data were analyzed separately with paired t tests for the effect of knee positions and one-way repeated measures analysis of variance for hip positions.
Results: At 20 degrees of knee flexion, there was no significant difference among the three hip positions, whereas at 40 degrees of knee flexion, medial rotation of the hip resulted in significantly higher vastus medialis obliquus over vastus lateralis activity ratio than lateral rotation (P < 0.05).
Conclusions: There was relatively more activation of vastus medialis obliquus than vastus lateralis at 40 degrees of semisquat with the hip medially rotated by 30 degrees. This finding has clinical implications for training the vastus medialis obliquus in patients with patellofemoral joint pain syndrome.