Tuesday, November 20, 2007

Sports Power Series, 2

It doesn't help you to continually get stronger if power development is not there also. Power, or speed strength (how fast your muscles can produce force) is one of the best physical predictors of success in sports.

Plyometric exercises help you to increase power. Traditional barbell and dumbbell strength exercises do not allow you to move at the speeds necessary to improve power. Strength training gives you the muscular and nervous system development needed to develop optimal power.

So how does plyometrics work (Integrated Performance Paradigm)? Primarily through the use of two components: 1) elasticity of the muscles and 2) the stretch shortening cycle.

Muscles can produce three types of contractions: eccentric (muscle lengthens and reduces force), isometric (length of muscle doesn't change and stabilizes force) and concentric (muscle shortens and produces force). The stretch shortening cycle produces more powerful concentric contractions.

Plyometric exercises always follow the same order: a landing phase, an amortization phase and the take off. The landing phase starts when the muscles start an eccentric contraction. The rapid eccentric contraction stretches the elastic component of the muscle and activates the stretch reflex.

A high level of eccentric strength is needed during the landing phase. Inadequate strength will result in a slow rate of stretch and less activation of the stretch reflex. The amortization phase, the time on the ground, is the most important part of a plyometric exercise.

It represents the time between the landing and the take off and is critical for power development. If the amortization phase is too long, the stretch reflex is lost and there is no plyometric effect. The take off is the concentric contraction that follows the landing. During this phase the stored elastic energy is used to increase jump height and explosive power.

Plyometrics represent high intensity training, placing great stress on the bones, joints, and connective tissue. While plyometrics can improve an athlete’s speed, power, and performance, they also place her or him at greater risk of injury than less intense training exercises.

It is important to perform the exercises correctly before implementation of full-speed exercises. Jumping and landing techniques should be mastered by the athlete. Exercises should also be performed on safe surfaces such as rubber mats, sprung floors, grass or sand. Concrete or other similar hard surfaces expose the athlete to injury.

And finally, the athlete should have good core and lower body strength to enhance the plyometric effect and reduce chances of injury.

Part 3 in this series will detail training guidelines for plyometrics.

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Mark Dilworth, BA, PES
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