This is an excerpt from Plyometrics by Donald A. Chu & Gregory Myer.
Determining the Proper Height for a Depth Jump
In practical terms, the task of determining the proper height for a depth jump centers on the athlete's ability to achieve maximal elevation of the body's center of gravity after performing a depth jump. If the height is too great for the strength of the legs, then the legs spend too much time absorbing the impact of the landing. As a result, the legs cannot reverse the eccentric loading quickly enough to take advantage of the serial elastic component of muscle and the stretch reflex phenomenon. The result is a jump that is dependent on strength and devoid of power. In this case, the athlete will spend a long time on the ground.
Coach and athlete should work to find the proper height—one that lets the athlete maximize the height jumped and also achieve the shortest amortization phase. A recent study supports this contention because it found that as drop jump height increased there was a subsequent increase in quadriceps activation. However, when the study participant dropped from 60 centimeters (about 2 feet), the ground contact time increased during the takeoff phase. In addition, the highest drop heights increased the peak vertical ground reaction force and resulted in a straighter knee when landing. The study authors argued that the altered muscular activation and movement patterns of the knee at the highest depth jump height diminished the effectiveness of plyometric training and increased the potential risk for knee injury.
The following procedure outlines one method described by many authors for determining maximum height for the depth jump:
- The athlete is measured as accurately as possible for a standing jump-and-reach. (For the standing jump-and-reach, suspend an object overhead or mark a target on a wall. The athlete stands with feet shoulder-width apart then squats slightly and explodes up, reaching for the object or target. The athlete should not step before jumping.)
- The athlete performs a depth jump from a box at a height of 24 inches (61 cm) for males or 18 inches (46 cm) for females, reaching as high as he or she can after takeoff, trying to attain the same height as measured for the standing jump-and-reach in step 1. (If the athlete cannot attain this height, see the note at the end of this procedure.)
- If the athlete successfully executes this task, the athlete may move to a higher box. The box height should be increased in 6-inch (15 cm) increments.
- Repeat steps 2 and 3 until the athlete fails to reach the standing jump-and-reach height. The previous box height then becomes the athlete's starting point for this drill.
Note: If the athlete cannot reach the standing jump-and-reach height from a 24- or 18-inch box, the height of the box should be lowered, or depth jumping should be abandoned for a while in favor of strength development. If the athlete cannot rebound from a basic height of 24 or 18 inches, the athlete probably does not have the musculoskeletal readiness for depth jumping.
Read more from Plyometrics by Donald A. Chu and Gregory Myer.