Plyometric training effects on Achilles tendon stiffness and dissipative properties.

The aim of this study was to determine the effects of 14 wk of plyometric training on mechanical properties of the Achilles tendon. Nineteen subjects were randomly assigned to trained or control group. Cross-sectional area (CSA), stiffness, and dissipation coefficient of the Achilles tendon were measured before and after the training period. In the trained group, a decrease in dissipation coefficient (-35.0%; P<0.05) and an upward trend in stiffness (+24.1%) of the Achilles tendon was found, without any changes in Achilles tendon CSA (P>0.05). Plyometric training enhances the muscular tension transmission mainly through a reduction in energy dissipated by the tendon. The lack of changes in the Achilles tendon CSA indicates that changes in mechanical properties would mainly result from a qualitative change in tendinous tissues rather than from changes in the geometry of the Achilles tendon.