The purpose of the study is to investigate the influence of contraction and relaxation times on the mechanical properties of human tendon. Ten healthy males participated in this study. They exerted ramp isometric plantar flexion torque with four conditions (1 s, 3 s, 5 s, 10 s) as each time of contraction (from rest to maximum) and relaxation (from maximum to rest) (exp. 1). In addition, eight of the subjects performed contractions and relaxations with 5 s and quick (contraction and relaxation as fast as possible) conditions (exp. 2). During the tasks, the elongation (L) of the tendon of medial gastrocnemius muscle (MG) was directly measured by ultrasonography. The mechanical properties of tendon (maximal L, stiffness, and hysteresis) were calculated from the relationship between the estimated muscle force (Fm) of MG and L. There were no differences in the L values at all the force production levels among the four conditions in exp. 1. On the other hand, the L values of quick condition were lower than 5 s condition at force development above 108 N. However, the mechanical properties of tendon (maximal L, stiffness, and hysteresis) did not differ among the five conditions. The present result indicated that the mechanical properties of human tendon were not influenced by the contraction and relaxation times.
