Many volleyball players are performing plyometrics exercises. But what exactly is plyometrics? This article outlines the essential basics behind how and why plyometrics works.

  

The development of plyometric training

Plyometrics is the term now applied to exercises that have their roots in Europe, where they were first known simply as “jump training.” Interest in this jump training increased during the early 1970s as East European athletes emerged as powers on the world sport scene. As the Eastern bloc countries began to produce superior athletes in such sports as track and field, gymnastics, and weightlifting, the mystique of their success began to center on their training methods.
The actual term plyometrics was first coined in 1975 by Fred Wilt, one of America’s more forward-thinking track and field coaches. Based on Latin origins, plyo + metrics is interpreted to mean “measurable increases.” These seemingly exotic exercises were thought to be responsible for the rapid competitiveness and growing superiority of Eastern Europeans in track and field events. Plyometrics rapidly became known to coaches and athletes as exercises or drills aimed at using strength with speed of movement to produce power. Plyometric training became essential to athletes who jumped, lifted, or threw.

The Science of Plyometric Training
Throughout the 1980s, coaches in volleyball began to use plyometric exercises and drills to enhance their training programs. The ’90s have seen a great deal of effort expended on attempts to verify the effectiveness and safety of plyometrics. Athletes of various sports and equally varied levels of conditioning have been compared to “untrained” athletes under all sorts of variables, and conditions. The point that is missed in this research is that athletic development follows its own time curve. A 6-, 12-, or 24-week testing period can in no way reflect the longitudinal develop?ment that will occur throughout an athlete’s overall career. For some, this time span may be a single season, for others, it may be up to 30 years of highly competitive activity:
Therefore, plyometric training should be considered in the context of the athlete’s age, skill levels, injury history, and a myriad of other variables that comprise his or her athletic development. In this way through applied research practitioners can learn to establish realistic expectations.

plyometrics jump 

The Physiology of Plyometrics

Plyometrics refers to exercise that enables a muscle to reach maximum force in the shortest possible time. The muscle is loaded with an eccentric (lengthening) action, followed immediately by a concentric (shortening) action.

How Plyometric Exercises Work
A muscle that is stretched before a concentric contraction, will contract more forcefully and more rapidly. A classic example is a ?dip” just prior to a vertical jump. By lowering the center of gravity quickly, the muscles involved in the jump are momentarily stretched producing a more powerful movement. But why does this occur? Two models have been proposed to explain this phenomenon.

Mechanical Model
In this model, elastic energy is created in the muscles and tendons and stored as a result of a rapid stretch. This stored energy is then released when the stretch is followed immediately by a concentric muscle action. According to Hill the effect is like that of stretching a spring, which wants to return to its natural length. The spring is this case a component of the muscles and tendons called the series elastic component.

Neurophysical Model
When a quick stretch is detected in the muscles, an involuntary, protective response occurs to prevent overstretching and injury. This response is known as the stretch reflex. The stretch reflex increases the activity in the muscles undergoing the stretch or eccentric muscle action, allowing it to act much more forcefully. The result is a powerful braking effect and the potential for a powerful concentric muscle action.

If the concentric muscle action does not occur immediately after the pre-stretch, the potential energy produced by the stretch reflex response is lost. (i.e. if there is a delay between dipping down and then jumping up, the effect of the counter-dip is lost). It is thought that both the mechanical model (series elastic component) and the neurophysical model (stretch reflex) increase the rate of force production during plyometrics exercises.

The Stretch-Shortening Cycle
All plyometric movements involve three phases. The first phase is the pre-stretch or eccentric muscle action. Here, elastic energy is generated and stored. The second phase is the time between the end of the pre-stretch and the start of the concentric muscle action. This brief transition period from stretching to contracting is known as the amortization phase. The shorter this phase is, the more powerful the subsequent muscle contraction will be. The third and final phase is the actual muscle contraction. In practice, this is the movement the athlete desires – the powerful jump or throw. This sequence of three phases is called the stretch-shortening cycle.