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Tuesday, October 09, 2007
Plyometrics refers to a type of explosive exercise. It combines concentric and eccentric muscle contractions. With a concentric muscle movement, the muscle shortens while it contracts. With an eccentric muscle contraction, the muscle lengthens while it is exerting force. (A third type of muscular contraction is referred to as an isometric contraction. In this case, the muscle does not lengthen or shorten but stays the same length while it is exerting force.) In plyometric exercise, eccentric muscle contraction is quickly followed by a concentric contraction. The eccentric movement stores elastic energy in the muscle, which adds to the speed and force of contraction when concentric movement occurs. Plyometric conditioning involves a series of rapidly alternating eccentric and concentric muscular contractions.
The classic type of plyometric exercise is jumping. During the landing phase, there is an eccentric muscle contraction in which leg muscles lengthen, and potential energy is stored. When the person then quickly contracts the leg muscles to jump, the thigh, calf, and buttock muscles shorten in a concentric fashion. Rapidly repeating the sequence of jumping and landing constitutes plyometric exercise. Similarly, hopping on one leg, skipping, or doing a triple jump are plyometric movements. Clapping push-ups are an example of an upper body plyometric exercise. Other upper body and trunk (core) plyometric exercises can be performed with the use of a medicine ball.
This type of training has been used by athletes for years to improve performance. Studies have shown that plyometric conditioning enhances muscular power - the ability of the muscle to generate a large amount of force quickly.
Plyometric exercises can be added to a standard strength training routine. You can also do plyometrics as part of an aerobic workout session. Plyometrics are not intended to be a stand-alone exercise routine.
Aerobic (cardiovascular) exercise improves endurance. It trains the muscle fibers to contract for longer periods of time. However, cardiovascular exercise does not significantly improve muscle strength; that is, it does not increase the peak power output of the muscle. In fact, some animal studies done on muscle cells indicate that prolonged endurance training, when not balanced with resistance training, results in a decreased ability of the muscle to generate power over time. Resistance or strength-training (using weights or other forms of resistance equipment) increases muscle mass. It increases the cross-sectional area of the muscle, but it may not enhance the speed of contraction of the muscle. Because plyometric exercise increases muscular power - the ability of a muscle to generate force quickly - it can be a good addition to a standard exercise program. Plyometric exercise fosters speed and agility, and this type of training can improve balance and coordination. Properly performed and supervised, it enhances athletic performance.
Plyometric exercise should be performed on a resilient surface - one that is somewhat soft or cushioned. A grass surface is O.K. A mat can be used to cover a hard gym floor and make it appropriate for jumping exercises. The American Council on Exercise states that a safe and effective plyometrics program stresses quality, not quantity, of jumps.
Plyometric exercise is not for everyone. This form of training is not designed for those who are in poor physical condition or who have orthopedic limitations. Experts agree that you should already be involved in a muscle conditioning program before you begin incorporating plyometrics into your fitness regimen. If you have arthritis of the knees, plyometric exercise may not be appropriate for you. This type of exercise results in more impact and a greater stress on joints. Hard surfaces should be avoided, and proper landing technique should be observed to dissipate impact forces. Safe landing technique from a jump includes landing from toe to heel and using the entire foot as a rocker to distribute impact force over a greater surface area. Avoid twisting at the knee when you land. It is important if you plan to engage in this type of exercise to also include stretching in your exercise routine. Make sure to warm up properly before performing plyometric movements. Allow plenty of rest between training sessions. It is recommended that a qualified fitness professional supervise plyometric training.For more about plyometric exercise, please see the following links: