The Stretch-Shortening Cycle: Why a Quick Dip Makes You Jump Higher
Quick Intro
The stretch-shortening cycle, or SSC, is the natural pattern in which a muscle is first stretched while active and then immediately shortens. The dip before a jump, the footstrike in running and the backswing before a throw all use it. Movements that use the cycle produce more force and power than the same movement started from a dead stop.
The Idea in Plain Terms
Try jumping from a still, deep squat position, held for a few seconds, and then jumping with a quick dip beforehand. The second jump is higher. Three explanations are generally given:
- Elastic energy. Tendons and other tissues work like springs. A quick stretch stores energy, and part of it is returned when the muscle shortens.
- Stretch reflex. When a muscle is stretched quickly, sensors called muscle spindles trigger a reflex contraction, adding extra activation.
- Preactivation and force build-up. The muscle is switched on before the stretch, so it is stiff and at higher force when the push begins. The muscle also has more time to build force during the stretch phase.
The cycle has three phases: an eccentric phase in which the muscle lengthens, a very brief transition called amortization, and a concentric phase in which the muscle shortens. The shorter the transition, the more stored energy is kept. A long pause lets the stored energy dissipate as heat.
Researchers divide the cycle by duration. A fast SSC lasts less than about 250 milliseconds, as in sprinting or a drop jump, and relies heavily on tendon stiffness and reflexes. A slow SSC lasts longer, as in a countermovement jump or a squat, and depends more on muscle force and coordination.
A Worked Example
A comparison of three jumps in a training session:
| Jump | SSC type | Notes |
|---|---|---|
| Squat jump from a held position | None | Tests pure concentric power |
| Countermovement jump | Slow SSC | Dip and jump |
| Drop jump from a low box | Fast SSC | Quick ground contact and rebound |
The ability to use the cycle well is a trainable skill and a quality that plyometric exercises develop.
What the Research Shows
The Finnish researcher Paavo Komi described the mechanics in the 1980s, including a 1984 review in Exercise and Sport Sciences Reviews, and showed that stretch-shortening movements produce greater force output than shortening alone. Studies using ultrasound have shown that muscle fibers can stay nearly the same length while the tendon stretches and recoils, which lets the muscle work efficiently.
Training studies support its trainability. A 2007 meta-analysis found that plyometric training improves vertical jump height. Adaptations probably include greater tendon stiffness, better timing of muscle activity and improved use of the reflex.
The relative contributions of elastic energy and the reflex are still debated and probably differ between movements.
Who It Suits
This concept helps:
- Athletes in jumping and running sports.
- Coaches choosing plyometric drills.
- Anyone curious about why bouncing movements are efficient.
How to Use It
- Practice quick, controlled dips and jumps.
- Keep ground contacts short for fast SSC drills.
- Build strength first, because the cycle needs a base of force.
- Progress from low to high intensity.
- Allow recovery between sessions, since tendons take time to adapt.
- Do the work fresh, not tired.
Common Misunderstandings
It is not only about reflexes.
It is not available if you pause at the bottom.
It is not relevant only for athletes.
FAQ
Why is a countermovement jump higher? Stored elastic energy and a pre-built force.
Do all muscles use it? Those that stretch and then shorten, in jumping, running and throwing.
Does stiffness help? Some tendon stiffness helps in fast cycles.
Does it fade with age? It tends to decline, and training helps.
Where This Comes From
Komi PV, 1984, physiological and biomechanical correlates of muscle function: effects of muscle structure and stretch-shortening cycle on force and speed (Exercise and Sport Sciences Reviews, 12, 81 to 121). Markovic G, 2007 (British Journal of Sports Medicine, 41, 349 to 355). The fast and slow cycle division follows common usage in biomechanics.
Related to: plyometric training, post-activation potentiation, the force-velocity relationship and the length-tension relationship. Exercises include Squat Jump.