Breaking points of human hamstring muscle-tendon complex: A cadaveric study

Hamstring strain injuries frequently occur during the late swing phase of running; however, the breaking strength of the human hamstring muscle-tendon complexes remains unclear. This study aimed to determine the breaking strength of human hamstring muscle-tendon complexes. To this end, seven cadaveric specimens preserved using the Thiel's method were examined. The biceps femoris long head (BFlh), semimembranosus (SM), and semitendinosus (ST) muscles were isolated and secured to a testing apparatus. Using a material testing machine, tensile load (P) was applied to the distal end of each muscle. The initial muscle length was defined as slack length (L) and displacement (ΔL) was recorded during elongation. Cross-sectional area (A) was measured at the muscle belly using ultrasonography. Muscles were passively elongated until failure, and strain (%, ΔL/L), stress (kPa, P/A), and Young's modulus (kPa, stress/strain) were calculated. The breaking point was defined as the yield point where stress plateaued while strain continued to increase. Breaking strain was significantly lower in BFlh (12.7 ± 0.9 %) and SM (12.1 ± 0.8 %) than in ST (14.1 ± 1.1 %). Breaking stress was significantly higher in BFlh (106.5 ± 32.2 kPa) and SM (121.5 ± 23.4 kPa) than in ST (57.3 ± 15.9 kPa) (P < 0.001). Young's modulus at the breaking point was significantly higher in BFlh (830.1 ± 216.2 kPa) and SM (992.9 ± 147.9 kPa) than in ST (402.4 ± 92.5 kPa). BFlh and SM displayed lower breaking strain and higher breaking stress compared to ST, demonstrating stiffer mechanical properties. These mechanical characteristics could partially explain why these muscles are more vulnerable to strain under conditions of high tensile loading.