The effects of cyclic stretching on tensile properties of the rabbitʹs skeletal muscle

Objective. To define the threshold of muscle injury with cyclic passive stretch. Design. The changes in the load-deformation curve of muscle-tendon unit were monitored until the failure point by an in vivo rabbit model. Background. Muscle injuries range in severity from a simple strain to complete rupture. Although strains occur more frequently than complete failures, only a few studies have investigated the phenomena of these sub-failure injuries. Monitoring of the continuum for stretch-induced injury allows us to define the threshold of stretch injury. Methods. Thirty rabbitsʹ triceps surae muscle-tendon unit preparations were used. One of the pairs (control) was stretched until failure; the other (experimental) was first cyclic stretched to either 12, 20 or 25% of the initial length of the muscle-tendon unit and then stretched to failure. Comparisons were made between the load-deformation curves of the experimental and control specimens. Results. When cyclic stretched to 12 or 20%, there were no significant changes existed in the biomechanical parameters except the deformation at the peak load. In contrast, all the biomechanical parameters except the ration of the energy absorption changed significantly after 25% strain cyclic stretch. Conclusions. A threshold for stretch-induced injury does exist. This can be reproduced at the 25% strain of the triceps surae muscle-tendon unit.