Plyometrics is the name for a type of exercise developed to increase a muscle-groups power to generate a large amount of force quickly. It may be used, for example, to improve the throwing power of a football quarterback or the effectiveness of a boxer's punch. Unlike traditional strength training exercises, plyometric exercises are performed quickly and explosively. The most common plyometric exercises include hops, jumps and bounding movements. One popular plyometric exercise is jumping off a box and rebounding off the floor back onto the box. Another is the clap push-up. Plyometric training exploits the muscles' cycle of lengthening and shortening to increase muscle power. Plyometric exercises start with a rapid stretch of a muscle (the eccentric phase) followed by a rapid shortening of the same muscle (the concentric phase).

Plyometrics can be traced to Russia approximately 40 years ago when it was developed for the Russian Olympic team. Dr. Yuri Verkhoshansky is credited with creating the principle, which at the time was known as "shock training". While observing athletes, he realized that they had more strength and power coming out of a higher altitude landing when their muscles were stretched as opposed to a normal jump. The word plyometric comes from the Latin "plyo" and "metrics" meaning "measurable increases", because his studies with elite athletes showed measurable increases using the technique.

There are thousands of plyometric exercises, ranging from low intensity leg hops to high intensity drills such as box jumps, frog leaps, and burpies. Although these are typically associated with plyometric training for the adult athlete, common games and activities such as hop-scotch, jumping rope and jumping jacks can also be characterized as plyometrics because every time the feet make contact with the ground the quadriceps are subjected to the stretch-shortening cycle. In fact, plyometrics are a natural part of many movements, as evidenced by the leaping, hopping and skipping seen when children play.

Physical fitness trainers have long used apparatus to assist with plyometrics. For example, one plyometric exercise involves catching and tossing a medicine ball to an assistant while the exerciser lies on his back. The triceps and chest muscles work both while they are lengthening during the catch and while contracting during the toss.

Plyometrics (and any impact exercise) can cause injury if you don't warm up first and follow prudent safety precautions. The force generated during these moves requires that athletes use them carefully and with proper training. They should only be attempted if you already have good levels of strength, flexibility, and balance. A safe and effective plyometric program stresses quality, not quantity. Safe landing techniques, such as landing from toe to heel from a vertical jump, and using the entire foot as a rocker to dissipate landing forces over a greater surface area are important to reduce impact forces. In addition, visualization cues, such as picturing oneself landing "light as a feather" and "recoiling like a spring" after impact promotes low-impact landings. When landing it is important to avoid excessive side-to-side motion at the knee. Landing forces can be absorbed through the knee musculature (quadriceps, hamstrings, and calf muscle) more effectively when the knee is bending primarily in only one plane of motion. Due to the potential for injury and numerous different types of plyometrics available, it is advisable to work with a physical fitness trainer if you plan to use them in your training.