Differences in activation patterns of knee flexor muscles during concentric and eccentric exercises

The purpose of this study was to clarify the activation patterns among knee flexor muscles during knee flexion exercises by electromyography (EMG) and muscle functional magnetic resonance imaging (mfMRI). Seven male volunteers performed knee flexion exercises with each unilateral limb at 120% of 1 repetition of maximum (1RM) and 50% of 1RM. EMG activity was recorded for the biceps femoris long head, semitendinosus (ST), semimembranosus (SM), and gracilis (G) muscles; mfMRI T2 values in the same muscles were measured at rest and immediately after exercise. The study found that EMG of the ST and G was significantly higher than that of the ST during the exercises at 120% 1RM. T2 value changes in the ST and G were significantly higher than in the biceps femoris long head (BFsh) and ST in both exercises. It was concluded that the activation patterns among knee flexor muscles during knee flexion were nonuniform for the respective muscles.