The vertical jump is one of the most explosive physical movements executed in sport. In a number of sports, the higher the athlete is able to jump, the greater the prospects of success in that discipline. Basketball and volleyball are the two most prominent examples of sports where that correlation is plain. The jumping ability of an athlete is also an indicator of overall athletic ability, as there is a clear relationship between the ability to jump and the running speed that the athlete will develop over short distances. The National Football League, where prospective players are subjected to various physical tests, requires every player to be tested for both vertical leaps and 40-yd (37 m) sprints, irrespective of the position played.
The defining characteristic of the depth jump is that the jump is preceded with the strong eccentric (negative) muscle action caused by dropping down from a raised surface, as opposed to a standard box jump where you start on the floor. This makes the depth jump a true plyometric movement, where the muscles are stretched suddenly (by the impact of the landing), producing a powerful shortening of the muscle fibers.
The simplest method to measure an athlete's vertical jump is to get the athlete to reach up against a flat wall, with a flat surface under his/her feet (such as a gym floor or concrete) and record the highest point he/she can reach flat-footed (the height of this point from the ground is referred to as "standing reach"); fingertips powdered with chalk can facilitate the determination of points touched on the wall. The athlete then makes an effort to jump up with the goal of touching the highest point on the wall that he or she can reach; the athlete can perform these jumps as many times as needed. The height of the highest point the athlete touches is recorded. The difference between this height and the standing reach is the athlete's vertical jump.