Medial-lateral hamstring electromyographic activity during maximum isometric knee flexion at different angles

The purpose of this study was to investigate knee flexion torque and changes in electromyographic (EMG) activity of the medial and lateral hamstrings during isometric knee flexion at different angles. Thirty-four subjects, 17 female and 17 male, between 21 and 33 years of age, with no history of right knee pathology volunteered to participate. Subjects were positioned prone on the Cybex II with their right lower extremity secured in knee flexion. Surface electrodes were placed over the medial and lateral hamstring muscles. Each test session consisted of nine maximal isometric knee flexion contractions. Three contractions, of six seconds each, were recorded at 30, 60, and 90 degrees of knee flexion. Recordings of maximum torque and averaged EMG were made by the Cybex II and the Bioscope, respectively. The results showed statistically significant findings: (1) decreased torque as knee flexion increased (P < 0.0005); (2) men demonstrated greater torque than women (P < 0.05); and (3) EMG activity for both the medial and lateral hamstrings decreased as knee flexion increased with differences between 90 and 30 degrees, and 90 and 60 degrees (P < 0.05). We concluded that the decrease in torque output with increased knee flexion is consistent with present knowledge. The coordinated pattern of declining EMG activity with increased knee flexion for both the medial and lateral hamstring muscles requires further investigation. Copyright (C) 1996 Elsevier Science Ireland Ltd.