Velocity-Dependent Stress Changes in the Hamstring Muscle-Tendon Complex: A Study Using Human Cadavers.

Hamstring strain injuries frequently occur during high-speed running, when muscle tension is markedly increased. Given the viscoelastic properties of muscle, stress during elongation is expected to be velocity-dependent. Therefore, this study investigated the effect of elongation velocity on the stress in individual hamstring muscles. Seven Thiel-embalmed cadaveric lower limbs were used to isolate the biceps femoris long head, semimembranosus, and semitendinosus muscles. Specimens were fixed to a testing apparatus and passively elongated to 10% strain at five elongation velocities (20-300 mm/min), while tensile load and displacement were recorded. Muscle cross-sectional area was measured using ultrasound to calculate stress. A two-way repeated-measures analysis of variance examined the effects of muscle and velocity on stress at 10% strain. The results revealed no significant interaction between muscle and velocity (p > 0.05); however, both velocity and muscle had significant main effects on stress (p < 0.001). Post hoc analysis indicated that stress increased significantly with velocity (20 mm/min: 44.6 kPa, 50 mm/min: 47.4 kPa, 100 mm/min: 50.8 kPa, 200 mm/min: 56.4 kPa, 300 mm/min: 61.1 kPa). These findings suggest that stress in the hamstring muscles increases with elongation velocity, which may contribute to the risk of strain injuries during high-speed running. However, the results should be interpreted in the context of cadaveric testing and elongation velocities that are substantially lower than those observed in vivo.