Biomechanical studies of triceps surae muscle injury

The triceps surae muscle of rabbit was dissected out and then stretched to failure by MTS BionixTM 858 machine. The results showed that the load-deformation curve of triceps surae muscle-tendon unit can be separated into four different portions: the first viscoelastic portion corresponds to the physiological range of motion; the second portion has micro failure; the third portion has macro failure; and the forth portion has rupture and separation of muscle parenchyma. Failure usually occurs at the muscular portion near the Musculotendinous (MT) junction for the soleus muscle and the distal MT junction in the lateral head of the gastrocnemius muscle. In distraction, faster stretch rate results peak tension force requirement and energy absorption greater. This suggested that the triceps surae muscle viscoelastically responds to the tensile loads. In denervated muscle, we found the function of nerve might have a protective mechanism that worked on the muscle-tendon unit by increasing the peak force and the energy requirement for failure.