There are three types of muscle contractions:
- Eccentric in which the muscle lengthens under tension. It is used to decelerate the body.
- Isometric occurs when the body comes to a complete halt.
- Concentric is a shortening contraction used to reaccelerate the body.
When a wrestler drives for a takedown, he may initiate his motion with a backward step, which "loads" the back leg muscles as they stretch in an eccentric contraction. The eccentric contraction of his leg muscles decelerates his body as the contracting muscle stretches and lengthens as "loads" the muscles. For an instant the muscles are in isometric contraction in preparation for an explosive concentric contraction as the leg drives forward for a successful takedown. It is important to remember that the rapid stretch of the muscle must be followed by an immediate rapid concentric contraction. Any delay will result in this stored energy being lost
The maximum force that a muscle can develop is attained during a rapid eccentric contraction. However, muscles seldom perform one type of contraction in isolation during athletic movements. When a concentric contraction occurs (muscle shortens) immediately following an eccentric contraction (muscle lengthens), the force generated may be dramatically increased. If a muscle is stretched, much of the energy required to stretch it is lost as heat, but some of this energy may be stored by the elastic components of the muscle. This stored energy is available to the muscle only during a subsequent contraction. This energy boost is lost if the eccentric contraction is not followed immediately by a concentric effort. To express this greater force, the muscle must contract within the shortest time possible. This whole process is frequently called the stretch-shortening cycle and is the underlying mechanism of plyometric training.