O3 Optimal Use of Elasticity

Title

The stretch-shortening cycle (SSC) takes advantage of the elastic energy stored in tendons and elastic components of the muscle during the eccentric phase (stretching) to increase strength and power in the subsequent concentric phase (shortening). Tendons are the main elastic stores: the Achilles tendon stores ~35 J per stride in runners and up to 100 J in jumpers. The optimal condition for the use of elasticity requires: (1) a sufficient stretching speed (fast preload), (2) a minimum transition time (t_trans) between the eccentric and concentric phases to prevent energy from being dissipated as heat, and (3) adequate tendon stiffness that allows sufficient deformation without excessive losses. Optimal stiffness balances storage capacity (higher with soft tendon) with speed of force transmission (higher with stiff tendon). In ground-running contact, the leg stiffness k_leg determines the amount of elastic energy stored and the natural frequency of rebound.

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