Functional difference between the proximal and distal compartments of the semitendinosus muscle.

[Purpose] The tendinous inscription divides the semitendinosus muscle into the proximal and distal compartments. It was hypothesized that there are functional differences between those compartments. [Subjects and Methods] Seven adult males performed knee flexion and hip extension in the prone position. An ultrasound device measured the decrease in the length of muscle fibers in the two compartments during these movements. The knee and hip joint angles were concurrently measured using a video camera. Pearson's correlation coefficients were calculated between the decrease in muscle fiber length in each compartment and joint angle. [Results] During knee flexion, decreased muscle fiber length was significantly correlated with increased knee flexion angle. During hip extension, there were no significant correlations for either compartment. Only the decrease in muscle fiber length in the distal compartment during hip extension tended to be negative; the other decreases in muscle fiber length tended to be positive. [Conclusion] Correlations did not reveal any functional differences. However, only the distal compartment elongated during hip extension. This result might show a functional difference and could be applied in clinical contexts during hip extension.