stretchshortening

The stretch-shortening cycle (SSC) describes the sequence by which a muscle-tendon unit experiences an initial eccentric (lengthening) action followed immediately by a concentric (shortening) action, producing greater force and power than a purely concentric contraction. The SSC relies on three interacting processes: storage of elastic energy in tendons and other series elastic elements during the eccentric phase; a short amortization (transient) phase; and a rapid concentric contraction that uses both the stored energy and reflexive neural activation.

During the eccentric phase, the muscle-tendon unit is actively stretched, which stretches cross-bridges and stretches the elastic elements of the tendon. If the stretch is rapid, muscle spindles are activated, triggering stretch reflexes that increase neural drive to the muscle. The amortization phase is the transition; its duration determines how much stored energy is retained for the subsequent contraction. A short amortization maximizes energy transfer; a long phase leads to energy dissipation as heat. In the concentric phase, the stored elastic energy is released, and neural activation augments force output, often resulting in higher jump height or sprint speed than a purely concentric action.

SSC performance increases with appropriate tendon stiffness, favorable muscle architecture, warm-up, and training that improves rapid activation and strength. It is fundamental to many movements, including running, jumping, hopping, and throwing. Training approaches such as plyometrics and reactive strength work target improvements in the timing and efficiency of the SSC by enhancing neuromuscular coordination and tendon properties.