Facts and Fallacies of Fitness What are Plyometrics Part 2

Plyometrics or the 'shock method' means precisely that - a method of applying mechanical shock to force the muscle to produce as much tension as possible. Depth jumps involving an explosive rebound after a relaxed drop from a height onto the ground are the best known form of lower body plyometrics. However, this shock loading may be imposed by any explosive action of the upper or lower extremities involving sudden changes of direction, not just with the legs. For example, a typical upper body plyometric drill is the rapid rebound throwing of a medicine ball between two athletes or off a mini-trampoline.

The plyometric method is characterised by impulsive action of minimal duration between the end of the eccentric braking phase and initiation of the concentric acceleration phase. It relies on the production of a very brief explosive-isometric and eccentric-isometric phase which precedes the release of the elastic energy stored in the tendons and other connective tissues of the series elastic component of the muscle complex during the eccentric deceleration phase. If the transition phase is prolonged by more than about 0.2 second, the action constitutes ordinary jumping and not classical plyometrics. A useful visualisation is to imagine that the surface being touched by the hands or the feet during the plyometric contact phase is red hot, so that any prolonged contact would be dangerous.

A distinction should be made between maximal plyometrics and sub-maximal plyometrics. Maximal plyometrics are low-repetition activities where the intensity of the depth jump or rebound exercise is such that maximal or near-maximal rebound tension is produced in the relevant muscles. Just like maximal strength training with weights, these powerful impulses are not meant to be imposed on the musculature every workout, nor are multiple repetitions even possible or advisable.

Moreover, a rest interval of 2-4 minutes is recommended between successive repetitions. Sub-maximal plyometrics involve mechanical impulses which do not produce maximal muscular tension, although they are still performed with a very brief contact phase with the floor or projected object. For example, lower box heights are used for depth jumps and the athlete does not strive to reach maximal rebound height. Rapid double-footed bouncing or low skipping on the spot are other typical sub-maximal exercises.