Probably one of the most commonly used (and abused) methods of performance-enhancement for sprinters and indeed all running and jumping athletes is "plyometrics." Plyometrics can be defined as movements that involve fast eccentric muscle actions followed by dynamic and explosive concentric actions. The best example of a plyometric drill that comes to mind is the classic "depth jump" exercise where an athlete drops off a box or step of some pre-determined height. Upon hitting the floor the athlete concentrates on explosively jumping into the air as high as possible. The purpose of this method is to "shock" the body and nervous system to produce higher levels of muscle tension and force than would normally be possible without the preceding drop.