O3 Optimal Use of Elasticity

Topic

This stretch-shortening cycle—the very same cycle described in another model within this set—utilizes the elastic energy stored by the athlete's tissue during the eccentric stretching phase to subsequently boost both the force and the final power output of that tissue during the ensuing concentric shortening phase.

The tendon serves as the primary elastic reservoir for this cycle: the heel tendon stores a significant amount of elastic energy during each of a runner's strides—matching the substantial quantity of energy defined in another model regarding this tendon—and an even greater amount during a jumper's leap.

Optimal utilization of this elasticity requires a sufficiently rapid stretching speed, a quick preload of the tissue, and a minimal transition time between the eccentric and concentric phases of the cycle; this is essential to prevent the stored elastic energy from dissipating as heat before it can be harnessed.

Furthermore, this optimal condition requires adequate tendon stiffness to allow for sufficient deformation without excessive loss of elastic energy: this optimal stiffness balances the tendon's storage capacity—which is greater in a more compliant tendon—against the speed of force transmission through the tendon—which is higher in a stiffer tendon—representing the same trade-off between stiffness and storage capacity established in another model within this set. Therefore, in this model—which was initiated by utilizing stored elastic energy—the runner's final leg stiffness (a parameter also established elsewhere in this framework) determines both the final amount of elastic energy stored during each stride and the natural frequency of the leg's rebound against the ground. As the runner's leg stiffness approaches the optimal value used to initiate the model, the final elastic energy stored during each stride consequently increases.

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