Effects of muscle architectures on the hamstring musculotendon dynamics in high-speed running.

Hamstring strain injuries are the most common injuries in soccer. The biceps femoris long head muscle (BFLH) is injured most frequently among the bilateral hamstring muscles. Some previous studies reported that the relationships between hamstring strain injuries and the hamstring muscle architectures. In particular, the optimal fiber length and the pennation angle of hamstring muscles have the large individual differences. However, the reason why the muscle architectures lead to the hamstring strain injuries is not clear. The purpose of this study was to investigate the effects of the muscle architectures, which we focused on the optimal fiber length and the pennation angle of BFLH, on the hamstring musculotendon dynamics in high-speed running. The results of this study showed increasing the optimal fiber length and decreasing the pennation angle lead to increasing the peak muscle force of BFLH during the late swing phase of high-speed running.