Effect of hip angle on neuromuscular activation of the adductor longus and adductor magnus muscles during isometric hip flexion and extension.

Neuromuscular activation of the adductor longus (AL) and adductor magnus (AM) muscles at different hip flexion angles during hip flexion and extension has not been clarified. This study aimed to compare the relationship between hip flexion angle and the electromyogram of the AL muscle with that of the AM muscle during isometric hip flexion and extension. Fifteen healthy young men were included in this study. Participants performed maximal voluntary contractions during hip flexion and extension at six different hip flexion angles: - 20°, 0°, 20°, 40°, 60°, and 80°. The surface electromyograms of the AL and AM muscles were recorded. The root mean square (RMS) was calculated and normalized by the RMS during hip adduction for each individual muscle. The normalized RMS of the AL muscle was significantly higher than that of the AM muscle at a hip flexion angle of - 20° during hip flexion (P < 0.05). The mean normalized RMS of the AM muscle was significantly higher than that of the AL muscle during hip extension (P < 0.01). These results suggest that the AL muscle is recruited specifically at the hip-extended position during hip flexion, and that the AM muscle is recruited regardless of the hip position during hip extension. Thus, the AL and AM muscles may have different functional roles in different hip flexion angles.