The purposes of this study were to analyze local strain of the Achilles tendon during exercise by finite element analysis with individual structural geometry and force data. Tetrahedral mesh models of Achilles tendon for finite element analysis were made from cross-sectional magnetic resonance images of eighteen subjects. The Achilles tendon deformation by maximal voluntary contraction was simulated by large deformation non-linear static analysis. Strain concentration was clearly observed at the portion from the proximal 20% to 50% length. The maximum principal strain was 13.5 ± 5.57 %. This portion was consistent with the highest risk portion of Achilles tendon rupture and /or inflammation related to exercises. Thus these results suggest that the evaluation of this portion would be important to increase the accuracy of estimation on the risk of Achilles tendon disorders. Also, the correlation analyses showed the risk is significantly correlated to the length of Achilles tendon.

The purpose of this study was to clarify the mechanical role of the springboard in the gymnastic vault from the viewpoint of mechanical energy. Ten male gymnasts performed five handspring vault trials with same apparatus set up as a gymnastics competition. The springboard was mounted on four force plates (1000Hz) embedded in the floor. The motions of the springboard and the gymnast were recorded by synchronized high-speed video cameras (500Hz) respectively. Force applied on the gymnast was calculated by subtracting the inertial force of the springboard from the ground reaction force, the leg stiffness of the gymnast was then defined as the ratio of the applied force to the leg length change during take-off motion. The take-off motion in the gymnastic vault was characterized by a large leg stiffness. The large leg stiffness induced a large deformation of the springboard and thereby enhancing energy transfer between the springboard and the gymnast’s body. The resultant returned energy from the springboard was approximately twice as large as that from the muscle-tendon complex of the gymnast. On the other hand, the energy lost from the springboard was larger than that from the muscle-tendon complex of the gymnast. It can be assumed that the main mechanical role of the springboard is to enhance the conversion of the initial kinetic energy to the potential and vertical kinetic energy of the gymnasts through take-off motion.