FAILURE SITES AND PEAK TENSILE FORCES OF THE COMPOSITE TRICEPS SURAE MUSCLE BY PASSIVE EXTENSION IN THE RABBIT

The triceps surae muscle-tendon unit of rabbit was tested by a passive extension technique. The effects of different stretch rates were eval uated. Functioning as a composite muscle-tendon unit, the triceps sura e responded viscoelastically to the tensile loads. The sites of failur e were consistent at the muscular portion near the musculotendinous ju nction. Failure occurred within 0.1-1.0 mm of the distal musculotendin ous junction for the soleus muscle and within 5-10 mm proximal to the distal musculotendinous junction in the lateral head of gastrocnemius muscle. In the medial head of gastrocnemius muscle failure occurred wi thin 15-30 mm proximal to the distal musculotendinous junction. There was a greater peak tensile force requirement and a greater energy abso rption when tested with faster stretch rates. These results furnish ev idence that the biomechanical property of composite musculotendinous u nit is strain-rate dependent and behaves viscoelastically. Relevance T riceps surae muscle is one of the most commonly injured muscles in cli nical medicine. However, information about the failure mechanism is st iff scanty. This study was aimed at making a contribution to the under standing of failure mechanism of the composite (as opposed to single) muscle-tendon unit, which may be useful in elucidation of the pathophy siology of triceps surae muscle injury in clinical medicine.