Plyometrics Primer - Part I

Players and coaches are always asking, “Coach, what are plyometrics?” What used to be called jump training was renamed plyometrics in 1975 by a track and field coach by the name of Fred Wilt. The word itself comes from the Latin plyo + metrics which means “measurable increases”.

Plyometrics are an important component of your athletic performance. The term is also used to refer to a training methodology used to develop explosive power. When utilized in combination with weight training methodologies, particularly maximal power output or complex training, plyometrics can provide strength and speed beyond your weight training program alone.

We’ve all heard someone say, “Now, that’s a powerful athlete!” Let’s examine exactly what that means. Power is the application of force through a range of motion in the smallest possible amount of time. Power is force times velocity, or speed-strength. Power, then, is the Holy Grail of sports specific training. So, how do we get from strength development in the weight room to speed-strength application on the field, on the ice, or on the court? One of the best ways to accomplish this lofty goal is through plyometric training.

In order to understand how plyometric training works, we must first understand something about muscle contractions. Every sport skill makes use of the three types of muscle contraction – eccentric, isometric, and concentric contractions. We will use the example of a high jumper to illustrate these three types of muscle contraction. As our athlete executes the run up, we notice a slight flexion at hip, knee, and ankle each time foot contact is made. Eccentric muscle contraction occurs as the muscle lengthens under tension and slows the descent of the body. This descent slows to a point, at midstride, where it stops and the body is, momentarily, in a static position. This lack of flexion or extension is referred to as the isometric contraction. There is no visible motion in either direction during the very brief period of time our high jumper takes to plant for the jump. Muscle fibres are, in fact, already shortening in preparation for the concentric contraction with no visible limb movement. Finally, the jumper’s hip, knee, and ankle begin their movement toward a full triple extension and the athlete leaves the ground in a powerful, explosive manner. The concentric contraction has resulted in an acceleration of the limb.

The transition from eccentric to concentric contraction is called the amortization phase. The stored, or potential, energy of the eccentric phase can be recovered, to a degree, in the concentric phase if ground contact time is kept to a minimum. The longer the pause in the amortization phase, the more energy lost to the generation of heat and the less energy available to create an explosive, powerful concentric contraction. Staying with our high jumper as an example, the ground contact time in the plant before the jump is an amazing 0.12 seconds! This type of short amortization phase should be the goal of our sports specific training to enable us to translate that speed-strength to our sport skill.

Plyometric training addresses sports specific need to shorten the amortization phase. Interestingly enough, shortening the amortization phase depends largely on learning, strength and “natural” speed play a role but any athlete can shorten their amortization phase by applying skills learned through plyometric training in combination with a foundation of strength development.

This has been the first in a series of articles about plyometrics. We have discussed something about what plyometrics are all about and the basics of how they work to make us better athletes. Future articles will concentrate on the stretch-shortening cycle, basic plyometric drills, periodized plyometric training programs, and the vertical jump.

Get after it!

Coach Jeff Jensen