Synergy of medial and lateral hamstrings at three positions of tibial rotation during maximum isometric knee flexion

Rotation of the knee has been used to isolate the strength of the medial and lateral hamstrings during manual testing of the knee flexors. The purpose of this study was to determine if medial and lateral rotation of the knee during manual knee flexor strength testing increased the electromyographic activity of the respective hamstrings. Twenty-three women between 22 and 36 years old with no history of lower extremity injury or disease participated in the study. Indwelling fine wire electrodes were used to record EMG activity of the medial (semitendinosus and semimembranosus) and lateral (long and short heads of the biceps femoris) hamstring muscles during maximally resisted knee flexion with neutral, medial, and lateral rotation of the knee. Repeated measures analysis of variance with post hoc Bonferroni adjustments were used to compare EMG activity across the three tests. EMG activity increased significantly for the target hamstrings during ipsilateral rotation ( P