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Plyometrics is a type of exercise that uses explosive movements to develop muscular power. Power is a combination of strength and speed. The ability to generate a force in a small time allows for athletic movements beyond what raw strength will allow. For example, an athlete who has strong legs and can perform the freeweight squat exercise with heavy weights may not be able to jump as high as another athlete who is not as strong, but who can generate more force in a small time. Plyometrics allows an athlete to develop more power because of the way muscles work. For a muscle to cause movement it contracts, this is known as a concentric contraction. There is a maximum amount of power with which a certain muscle can contract. However, if the muscle is lengthened (eccentric contraction) just prior to the contraction, it will actually produce more power. This effect depends on the time between eccentric contraction and concentric contraction being very short. It is theorized this extra power is due to the muscle gaining potention energy much like a rubber band does when stretched. This energy dissipates rapidly, so the action must be quick. The process is frequently refered to as the "stretch shortening cycle" and is the underlying mechanism of plyometric training. Most exercises involve a muscular contraction that starts off rapidly, but decelerates suddenly before the end of the repitition. For example, lifting a barbell involves jerking the weight quickly into the air, then bringing this motion to a sudden stop. Plyometric exercizes are characterized by the lack of such a decelerative phase. They are open-ended movements into free space. Other animals take advantage of this same effect. One example is the kangaroo. If a kangaroo needed to use 100% new energy to contract its leg muscles everytime it jumped, it would not be able to go very far. However, because of the muscles ability to store energy from the jump before like a spring, the kangaroo only needs to use a fraction of the total energy in the jump. Physical educators have long used various apparatus—including medicine balls, jump ropes, and Indian clubs. One plyometric exercise involves catching and tossing a medicine ball to an assistant while the exerciser lies on his back. The triceps and chest muscles are working both while they are lengthening (catch phase) and while contracting (toss phase). The clap press-up is another example of a plyometric exercise. Plyometric exercises carry increased risk of injury, and should only be performed by well-conditioned individuals who are under supervision. Plyometrics is used to develop explosive speed, and focuses on power instead of raw strength or muscle mass. Plyometrics may be used, for example, to improve the effectiveness of a boxer's punch, or to increase the vertical jumping ability of a basketball player. Data originally published on Wikipedia |