The Stretch-Shorten Cycle and Vertical Jump

A stretch-shorten cycle (SSC) is defined as an eccentric contraction followed by an immediate concentric contraction.  The shortening (concentric) phase of a SSC is more powerful, does more work, than the shortening (concentric) phase of a concentric only contraction.  The extra work performed during the shortening (concentric) phase of a stretch-shorten cycle is attributed to the following:

  1. Stored elastic energy, during the stretch phase of the motion elastic structures in the muscle store elastic energy which is returned during the concentric phase of the motion.  The transition between eccentric and concentric must be immediate for the elastic energy to be returned.  If the transition between eccentric and concentric is not immediate the energy is dissipated within the muscle.
  2. The eccentric phase of the motion elicits a stretch reflex which then increases the activation of the muscle that was stretched resulting in a more forceful contraction.
  3. Since the eccentric phase of the stretch-shorten cycle preloads the muscle – tendon complex it causes the concentric phase of the SSC to start at a higher force level than does a concentric only contraction.
  4. Two joint muscles contribute to additional work performed during a SSC.  For example, during the extension phase of a vertical jump the knee is extended, which shortens the rectus femoris while the hip is simultaneously extending which lengthens the rectus femoris.  The net effect of shortening the rectus femoris at the knee while lengthening it at the hip results in the muscle length remaining relatively constant.  As a result the muscle performs work at a more optimal length on the muscles force – length curve and it contracts at a slower velocity which yields a higher force level on the concentric side of the force – velocity curve.

KINE 4300 Vertical Jump Projects

Anu Shrestha, Effects of velocity of stretch on countermovement jump. Applied Exercise Physiology KINE 4300 research project. Advisor: Dr. Mark Ricard.

[Currently waiting for IRB approval] Contact Anu to be a subject