If you want to lower your mile run time, would you cross-train by taking up swimming? If your golf game is suffering, would you work on your golf swing by playing tennis? Granted, swimming and tennis are great sports, but in terms of achieving goals, it’s a case of “the wrong tool for the wrong job.” This analogy also applies to the use of plyometric box jumps in workouts designed to improve athletic fitness.
Plyometric box jumping is a method of training that should be restricted to athletes who want to develop power. Power is technically defined as “the rate at which work is performed” or “the product of force multiplied by velocity.” Strength coaches sometimes regard power simplistically as the ability to exert force quickly.
Another way to think about power is by way of example. Here are a few athletes whose performances are synonymous with the word power: LeBron James (basketball), Michael Phelps (swimming), Serena Williams and Novak Djokovic (tennis), Adrian Peterson (football), Wladimir Klitschko (boxing), Brock Lesnar (MMA/Pro Wrestling), Miguel Cabrera (baseball), Zdeno Chara (hockey), Dmitry Klokov (weightlifting), McKayla Maroney (gymnastics), Shelly-Ann Fraser-Pryce and Usain Bolt (sprinting), and Tomasz Majewski (shot put). Got the idea?
In the US, plyometric box jumping is often used as a method of conditioning. For example, an individual might perform a set of chin-ups or push-ups for the upper body, and then finish off by jumping onto and off a box for 10-15 reps. Such a program requires relatively inexpensive equipment, can be performed in large groups and really gets the heart pumping. However, for developing power this type of program design is a poor idea, which becomes clear when you follow the science.
The Science of Power Development
A motor unit is a nerve that activates a muscle or group of muscles, and high-threshold motor units create the most powerful muscular contractions. One way to recruit these motor units and thus improve power is with plyometrics.
One characteristic of a plyometric activity is it involves a rapid lengthening of muscles (eccentric phase) and is immediately followed by a rapid shortening of those muscles (concentric phase). Such an activity produces two effects: (1) a reflex increase in muscle tension and (2) the release of elastic energy stored in the muscles and tendons. However, simply jumping onto a box does not create enough muscle tension to create a significant plyometric effect.
To develop a high level of muscle tension, you want to create what is known as a “mechanical shock stimulation” (MSS). An example of an MSS is to step off a box and then focus on immediately jumping upward upon landing. The higher the box, the greater the MSS and the muscle tension – to a point. If the box used is so high that the height of the rebound begins to diminish, the athlete will be forced to spend too much time on the ground and thus will be unable to effectively utilize the stored energy developed during the landing.
Another issue is that fatigue interferes with the ability to recruit these high-threshold motor units of the muscles. You need to be fresh when you go into a plyometric box jump exercise, and this necessitates longer rest periods. As such, the circuit program described earlier would not be an effective way to incorporate plyometric box jumping into a workout.
How effective is plyometric box jumping? Numerous studies have shown that plyometric training, by itself, can improve vertical jumping ability, which is a standard measurement of lower body power. However, a more effective approach can be to combine plyometric training with conventional weight training. One study on this approach was published in the Journal of Applied Sports Science Research, 1992, vol. 6, issue 1.
This study lasted six weeks and focused on determining which of three training protocols (squats, plyometrics or a combination of both) produced the greatest improvements in the vertical jump. The group that performed only squats increased their vertical jump an average of 3.30 centimeters (1.29 inches), and the group that performed only plyometrics increased their vertical jump 3.81 centimeters (1.5 inches). However, when plyometrics were combined with squats, the increase in the vertical jump was 10.67 centimeters (4.2 inches). For a practical example of how to design such a workout, consult Charles Poliquin’s article “Secrets to Maximum Power Development.”
An important note: Trainees who are going to use box jumping as a form of conditioning should jump onto the box and then step down rather than jumping down. Jumping off a box is more stressful than jumping onto a box, which involves less impact in the landing. Using plyometric box jumps as a form of energy system conditioning, especially for high repetitions and as part of a circuit, is simply too stressful on the bones and connective tissues and increases the risk of injury. It also will do little to develop power.
When used properly as described here, plyometric box jumping is a great tool for developing athletic power. It may not enable you to hit a serve as hard as Serena Williams or run as fast as Usain Bolt, but it will help you fulfill your athletic potential.