Influence of altered knee angle and muscular contraction type on electromyographic activity of hamstring muscles during 45° hip extension exercise

In this study, we investigated differences in electromyographic activity in the biceps femoris long head (BFl), semitendinosus, and semimembranosus muscles during 45° hip extension with different knee angles during eccentric, concentric, and isometric hip 0°, and isometric hip 45° conditions with non-external resistance and 5-kg load. Twenty-two male volunteers performed 45° hip extension with knee flexion angles of 0°, 45° and 90° with non-external resistance and 5-kg load eccentric, concentric, isometric hip 0°, and isometric hip 45° conditions. The electromyographic data obtained during each condition were normalized with the values collected during maximal voluntary isometric contraction of each muscle. A multivariate analysis of variance with repeated measures using syntax was used to compare the normalized elec-tromyography of each muscle across different knee joint angles in each weight condition. Electromyographic activities of the BFl, semitendinosus, and semimembranosus at 45° and 90° knee flexion angles were significantly greater than at 0° in the eccentric, concentric, isometric hip 0°, and in isometric hip 45° conditions with both non-external resistance and 5-kg load (p<0.05), except for that of the BFl and semitendinosus in isometric hip 45° with 5-kg load. The electromyographic activity of the BFl was significantly higher than that of the semimembranosus at 90° knee flexion in all conditions (p < 0.05), except during eccentric with non-external resistance. There was no significant difference in electromyographic activity in the hamstring muscles among different knee angles and muscular contraction conditions. This study showed that 45° hip extension with 45° and 90° knee flexion might be better in terms of the recruiting hamstring activity com-pared to 0° knee flexion, regardless of the training intensity. We recommend 45° hip extension exercises with knee flexion angles of 45° and 90° to activate the BFl, in preventing hamstring strain.