Relationship Between Achilles Tendon Stiffness and The Eccentric Phase Duration of the Stretch-Shortening Cycle During Shock Plyometric jumps

Introduction: The Purpose of the present research is to investigate the relationship between Achilles tendon stiffness (ATS) and time of the eccentric phase (EP) of SSC during shock plyometric exercises.Tendon stiffness “describes the relation between the force exerted on the tendon and its change in the length” (Kubo et al., 1999). Shock Plyometric exercises are one of the most popular methods of developing power specially for the lower body. Therefore, a stiff tendon might be advantageous due to the quick force transmission from the muscle to the bone. We can hypothesis that a stiff tendon relates to shorter eccentric phase (EP) and greater ground reaction force (GRF) during the concentric phase of the SSC during shock jumps. Methods: Nineteen physically active healthy males (mean ± SD: 26.7 ± 3.9 years, 1.77 ± 0.07 m, 76.5 ± 6.7 kg) participated in this study. Subjects were asked to perform depth jumps on a force plate to determine GCT. We then simultaneously measured isometric maximum voluntary contraction (MVIC) of the plantar flexors with a dynamometer and recorded the elongation of Achilles tendon with ultrasound; hence, we could calculate tendon stiffness. Results: show a correlation between the time of the eccentric phase (EP) and Achilles tendon stiffness (ATS) (r = −0.546) and ground reaction force (GRF) (r = −0.464) during the concentric phase of SSC, respectively. Conclusion: According to the results, we can confirm the main hypothesis that a stiff Achilles tendon tends to result in a shorter EP during depth jumps.