Microfailure of peroneus longus muscle during passive extension.

To study the material properties of the skeletal muscle-tendion unit, the peroneus longus muscle of a rabbit, rubber and plastic materials were tested with on MTS machine. After anesthesia, the peroneus longus muscle of a rabbit was dissected out and then stretched to failure by an MTS Bionix 858 machine. The load-deformation curves of the muscle and non-biological materials were analyzed and compared. The results showed that the load-deformation curve of a muscle-tendon unit can be separated into 4 different portions: first, the viscoelastic portion, which corresponds to the physiological range of motion; second, the portion of microfailure; third, the portion of macrofailure; and fourth, the portion of rupture and separation of a muscle-tendon unit. The cause of these behaviors are explained by the presence of actinmyosin cross bridges. Elucidation of the existence of microfailure of skeletal muscle gives a good reference point to determine the functional capabilities and limitation of muscular tissue. This will be useful in determining the beneficial effect of stretch programs in sports and rehabilitation and preventing the potential impact of tissue injury.