Books written on plyometrics, and coaches who use plyometrics in the training of athletes do many different kinds of jumps under the umbrella name of plyometrics. However, even though most plyometric exercises involve jumping, not all jumps are plyometric. There are many different kinds of jumps and they should be differentiated.
For example, skipping rope, easy jumping and skipping, in which you get off the ground only a few inches, should not be considered plyometric. Nor should easy jumps for greater height be considered plyometric. They should simply be considered jumps.
In a true plyometric jump, the landing and take-off must be executed in approximately .15 seconds. If it takes longer, as for example, when the feet are in contact with the ground for long time, as occurs when going into a deep squat on each jump, it is no longer considered to be a true plyometric jump.
In such cases the built-up tension in the muscles, as a result of the eccentric contraction on initial contact in the landing, is diminished or dissipated. You then have to generate all the force needed to leap up into the air. In a true plyometric jump you rely on the built-up tension created on the landing to leap up into the air. This is a major distinction between these two types of jumps.
However, jumps or jump training, that is not truly plyometric in nature is still beneficial. Jumps are used in jump training, which usually precedes true plyometric training. It is still important to do both types of jumps to fully develop an athlete especially one who must jump or run in his or her sport.
Because of the confusion that surrounds plyometric training and what constitutes a true plyometric jump, it is necessary to label all true plyometric jumps as explosive jumps. This is what Dr. Yuri Verkhoshansky, who was considered the father of plyometrics, envisioned when he developed this type of training.
He originally called this method shock training as there is an initial ”shock” to the body to create the energy needed for the takeoff. The shock to the body automatically elicits an eccentric contraction of the involved muscles. In this contraction energy is accumulated and then quickly given back in the return movement.
Jumps use a different physiological mechanism. Suffice it to say that explosive plyometrics entails maximal loading of the muscles and a very quick response, i.e. takeoff. Jumps have a slower and lower response.
See Explosive Plyometrics for more details.