What are Plyometrics?
If you want to jump higher, sprint faster, hit harder or throw farther, plyometrics is the ideal exercise methodology employed. The practice is designed to increase speed and strength where it counts, in the movements directly related to the sport you pursue, and this means more power and better results from that action.
How The Muscle Works
There are two basic types of contraction of a muscle that are involved in plyometric training, these are termed, concentric (muscle shortens) and eccentric (lengthening of the muscle).
If you are still not completely sure of how these types of contractions work here is a breakdown and an example from Wikipedia http://en.wikipedia.org/wiki/Muscle_contraction
In concentric contraction, the force generated is sufficient to overcome the resistance, and the muscle shortens as it contracts. This is what most people think of as a muscle contraction.
In eccentric contraction, the force generated is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract. An eccentric contraction is used as a means of decelerating a body part or object, or lowering a load gently rather than letting it drop.
If you want to think of this in terms of a sport, let's use the baseball pitcher as an example. The effort to force the ball or throw it through the air is our concentric or agonist contraction and eccentric action from the antagonist muscles are used to slow the arm down (like brakes if you will) and prevent severe injury.
The greatest force from a muscle comes from a quick eccentric contraction, however because a muscle very rarely performs only one type of contraction in a given action, having a concentric contraction follow an eccentric contraction can really increase the power that is generated.
Taking this further, if we stretch the muscle, the energy or much of it used to actually stretch it is lost as heat. However some of this energy is stored by the elastic components of the muscle and can be utilized during a following contraction. This means you have to have a concentric contraction immediately follow an eccentric one to take advantage of this stored energy. This is referred to as the stretch shortening cycle and is the backbone of plyometric training.
Preparing for Plyometrics Training
Due to the nature of this explosive type training a great amount of stress is put on our musculoskeletal system. Because of this it is important that the athlete has a decent base in strength and endurance. If you are someone who has never trained before, especially if you have never done any type of resistance training such as weight training it is strongly recommended that you do not attempt plyometrics until you have a fair amount of that type of training under your belt.
It is also generally recommended that preadolescent and even adolescent athletes avoid plyometrics or at least the more advanced types due to immaturity in the skeletal system. If you intend to train a young athlete with these methods great care needs to be taken.
The Sport Determines The Training
The key to a successful plyometrics training or any sports specific training is just that...specificity. This is where the athlete or coach can be creative in the exercises, and through a solid understanding of the discipline that your are training for develop appropriate exercises that most closely mimic the actions that are used in the discipline. Keeping the following requirements in mind when you are developing these methods, ensure that there is a pre-stretch first, specificity, and to make the contact time (also known as ground contact time or coupling time) as short as possible. It's more important in plyometrics that the action be faster than longer.