Plyometric exercise (or shock training as it was known then) was first developed for Soviet athletes, and came to worldwide attention in the 1970’s.
Plyometric exercise is a form of exercise that utilises the stretch-shortening cycle of the muscle-tendon unit, first allowing for stretching of the muscle which builds up the potential energy, and then allowing a rapid shortening which exerts force. An example of this is jumping from a height and as soon as you land, jump as quick as you can vertically in one fluid movement.
Try it yourself and see how it works. First get into a half squat position and hold that position, next try and jump as high as you can beside a wall. Mark that height on the wall. Next, you’re going to do the same jump but with a mini-jump beforehand. Make sure when you land on your mini-jump that you squat down to the same position of the first jump, before you jump.
Plyometrics have been shown in many studies to improve performance in athletes, increase strength and power and also to prevent injury. It has more recently been shown to be an effective way to re-introduce an injured athlete to sport.
Below is a video of early plyometric exercises.