The Stretch-Shortening Cycle Explained: Why Some Athletes Are Just Built Differently
Summary
The stretch-shortening cycle is the mechanism that makes elite jumpers and sprinters seem almost effortless. Understanding how it works—and how to test and train it—explains a lot about athlete potential.
Some athletes produce power that their strength numbers cannot explain. They jump higher than their squat suggests they should. Their sprints look easier than the times on the clock. This is not a mystery — it is the stretch-shortening cycle (SSC) at work.
What the SSC Is
The SSC is a sequence of three muscular actions: an eccentric pre-stretch, a brief amortisation phase, and a concentric contraction. When a muscle is rapidly stretched under load before it contracts, it stores elastic energy in the series elastic component — tendons and other connective tissue — and the muscle spindles fire a myotatic reflex that potentiates the subsequent contraction. The result is a concentric force output significantly greater than could be achieved by a concentric-only effort.
Komi (1984) described this mechanism in detail, establishing that the SSC enhancement is real and substantial — not a training artefact. The magnitude of the benefit depends on the speed of the eccentric phase (faster stretch = greater recoil), the load, and the timing of the amortisation phase (shorter = better energy return).
Slow and Fast SSC
The SSC operates differently depending on the ground contact duration involved:
Slow SSC (contact time > 250ms) is what you see in squats, broad jumps, and countermovement jumps. There is time for deliberate pre-loading. Training the slow SSC involves loaded plyometrics, Olympic lifting derivatives, and heavy squats performed with a controlled eccentric.
Fast SSC (contact time < 250ms) is what happens in sprinting, drop jumps, and bounding. The contact time is too brief for voluntary control of the amortisation — the system has to be pre-stiffened, and the reflex response must be highly trained. This is why elite sprinters have high leg stiffness and short ground contact times that cannot be consciously coached into existence — they must be developed through years of appropriate training.
Why Some Athletes Seem Built Differently
Genetic factors in tendon stiffness, fibre type distribution, and reflex sensitivity mean that some athletes utilise the SSC more efficiently than others. An athlete with naturally stiff Achilles tendons stores and returns elastic energy more effectively with every stride. This accounts for a component of elite sprinting and jumping performance that is genuinely difficult to close through training alone.
This is not defeatism. SSC utilisation is trainable — significantly so. But it helps coaches and athletes set realistic expectations. An athlete who tests poorly on fast SSC tasks (low RSI, high ground contact times) but well on slow SSC tasks (good CMJ, good squat) has an identifiable training gap, not a permanent ceiling.
Testing SSC Utilisation
The most practical tests are:
- CMJ vs Squat Jump comparison: The difference in jump height between these two tests (sometimes called the pre-load benefit or reactive strength ratio) reflects the slow SSC contribution.
- Drop Jump RSI: Ground contact time and jump height combined into a ratio. Fast SSC efficiency in a nutshell.
- Rebound jump protocols: Consecutive jumps with minimal ground contact time, measuring height and contact time continuously.
Bosco et al. (1982) established the early framework for using these comparisons diagnostically. The CMJ–SJ difference is among the most robust and easily obtained indicators of SSC function in a field setting.
Training Implications
Improve SSC function through progressive plyometric loading, with particular attention to the rate of stretch (not just the magnitude), the landing mechanics preceding reactive efforts, and adequate strength as a foundation. An athlete who cannot control the eccentric phase will not benefit from SSC training — they will simply accumulate joint stress.
Build the base, then build the bounce.
References
Mark Fisher
More from Sports Science
