What is the stretch-shortening cycle?
The stretch-shortening cycle is the rapid sequence of an eccentric stretch, a very brief transition, and a powerful concentric contraction. Stored elastic energy and reflexive muscle activity make the resulting movement more forceful than a purely concentric effort.
The three phases
- Eccentric: The muscle-tendon unit lengthens under load, storing elastic energy in the tendon, as in the dip before a jump.
- Amortisation: The transition between lengthening and shortening. This is the critical phase, and it must be brief.
- Concentric: The muscle shortens, adding the stored elastic energy to the active force being produced.
Why the transition time decides everything
Elastic energy stored in a tendon dissipates as heat within a fraction of a second. If the amortisation phase is too long, that energy is lost and the movement becomes a purely concentric effort. This is why a countermovement jump beats a paused squat jump, and why the goal in reactive training is minimising ground contact time rather than jumping as high as possible.
Fast and slow versions
Contacts under roughly 250 milliseconds are considered fast: Sprinting, pogo hops, and depth jumps. Longer contacts are slow: A countermovement jump or a change of direction. Both are trainable, and they respond to different exercises, which is why programmes progress from slow to fast rather than treating all jumping as one quality.
How to train it
Start with pogo hops and ankle hops for stiffness and short contacts. Progress to countermovement jumps and broad jumps, then to depth jumps once landing control is solid. Cue "quick off the ground" rather than "jump high" when the goal is the reactive quality.
What limits it
Tendon stiffness, the ability to tolerate high eccentric loads, and coordination all matter. Strength provides the foundation, since the eccentric phase involves absorbing large forces. Detail is in The Stretch-Shortening Cycle and Reactive Strength and Elastic Qualities.
