Plyometrics Plyometric Training Program Plyometrics are exercises designed to specifically train the eccentric contraction phase of a muscle's action.
Eccentric contractions occur when the muscle lengthens under tension to decelerate the body.
For example, when a runner's foot strikes the ground the quad muscle must contract to prevent the leg from collapsing. Contrast this with a concentric contraction which involves contraction of a muscle while it shortens. An example would be leg extensions on a nautilus machine in the gym. The quad contracts and shortens to extend the leg and straighten the knee. Concentric type exercises are far more common and widely practiced than eccentric exercises.