Question

Describe the stretch-shortening cycle (SSC). Then discuss how the elastic properties of muscle and the Series Elastic Components (SEC) relate to each other. How do proprioceptors facilitate the speed at which plyometrics are accomplished, and specifically, the SSC? Finally, what is the goal of plyometric training with respect to changing the duration of phases within the SSC?

Answer 1

Plyometric exercises have three distinct phases, an eccentric phase, an amortization phase, and a concentric phase that releases the explosive force. These three phases make up a stretch-shortening cycle.

A stretch-shortening cycle (SSC) is an active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle.
The three phases.
Phase I is the eccentric phase, wherein, stretch of the agonist muscle takes place. During this phase, elastic energy is stored in the Series Elastic Components (SEC) and muscle spindles are stimulated.

Phase II is the amortization phase, which is the pause between phase I and phase II. In this phase, Is afferent nerves synapse with alpha motor neurons. Alpha motor neurons transmit signals to agonist muscle group.

Phase III is the concentric phase, wherein shortening of agonist muscle fibres takes place. During this phase, elastic energy is released from the Series Elastic Components (SEC) and alpha motor neurons stimulate the agonist muscle group.

The proprioceptors of the body include the muscle spindle, the Golgi tendon organ (GTO), and the mechanoreceptors located in joint capsules and ligaments. plyometrics are exercises that involve a jumping or explosive movement. Stimulation of the proprioceptors can cause facilitation, inhibition, and modulation of both agonist and antagonistic muscles.

Stretching of the muscle spindle increases the afferent nerve firing. The rate of the applied stretch deternes the strength of the signal that is sent to the spinal cord from the muscle spindle. So, if the rate of the stretch is faster, then the neurological signal sent from the muscle spindle will be stronger. This results in greater contraction of efferent muscles. (the shortening cycle of the plyometric movement). GTO acts as a protective reflex preventing over‐contraction or too much tension in the muscle. Thus, the GTO assists with modulating forces during plyometric exercises.