PRORehab Library

Concepts of Plyometric Exercise

Shawn Garlock, ATC

Plyometric exercise is an essential component to any athlete’s training program. Plyometric training is utilized to increase explosiveness, vertical jumping, horizontal jumping, speed, and body awareness. Athletes, regardless of the sport they participate in will benefit from plyometric training since it increases the amount of power an athlete produces during athletic performance. Power is defined as strength x speed. Therefore, an athlete who trains plyometrics will have an increase production of speed and strength, resulting in an overall increase in power. Additionally, plyometric exercises will have a positive affect on athletic success since the athlete will be trained to create muscular forces in the quickest amount of time as possible. Whatever the sport, plyometric training will increase the athlete’s production of power resulting in an increase of over-all athletic performance that transforms into an increase of athletic success on the playing field.

How does plyometric training increase the amount of power produced by an individual? There are two accepted models that explain how plyometric exercise has a positive correlation with the production of power. The first model is the stretch reflex response. This model suggests by applying a rapid stretch during exercise there will be increase activity in the muscle fibers. The increase activity in the muscle fibers results in an increase of muscular force produced by the fibers. For example, a bungee jumper preparing to leap off a bridge has the ability to create a great deal of force once a stretch is applied to the bungee rope. The stretch increases the activity of the cord’s fibers, producing large amounts of force that propels the jumper high into the air.

Another theory that attempts to explain how plyometric training increases power is the mechanical model. The mechanical model simply states that energy is stored in the muscle tendon. Once a stretch is applied to the muscle tendons and then rapidly released during a muscle contraction an increase of muscular force production occurs. The increase in force production is contributed to the muscles and tendons elastic response to return to their natural length prior to the stretch. The mechanical model is similar to a rubber band. Once a stretch is applied to a rubber band, it creates tension or stored energy, which is utilized to create a rapid contraction so it may return to its original length. Even though experts agree that both models have significant contributions to plyometric training, it is unclear to what proportions each model has on the effect of power.

While performing plyometric exercise there are three phases that must be executed that are essential for the production of power. The first phase consist of a rapid stretch that stimulates muscle spindles for the purpose of generating additional muscle contractions, which is called eccentric loading. The eccentric loading phase is an important component of plyometric training since both models require a stretch in order for increased muscle production to occur. The second and most critical phase is amortization. The amortization phase is the time from ground contact to the reversal of movement. This phase is the most important link to the production of power due to the correlation of duration and power. The shorter the duration of the amortization phase the greater the increase in power. Likewise, the longer the duration of the amortization phase, the greater the decrease in power. The concentric phase is the last phase during plyometric exercise. During this phase, the stored energy from the eccentric phase is either used to increase the amount of force produced by the muscle fibers or released as heat depending on the length of the amortization phase. Consider the rubber band example used to describe the mechanical model and apply it to the phases of plyometric exercise. The application of a stretch to the rubber band is considered eccentric loading. The amount of time it takes to stretch the rubber band and the speed, which the rubber band is released, describe the amortization phase. The concentric phase consists of the amount of force produced while the rubber band contracts in order to return to its original length.

Now that there is a basic understanding of the physiology of plyometric exercise, there are several guidelines that need to be addressed before an athlete begins training. Firstly, the athlete must be able to squat a minimum of fifty percent of their body weight and at least 200 percent for more intense exercises. If the athlete does not have enough strength to meet the squat requirement, then emphasis should be placed on a strengthening program rather than plyometric exercise in order to prevent injuries. Always utilize non-slip surfaces to avoid falling or slipping accidents. Provide an appropriate warm-up that increases the heart rate and prepares the body for high impact exercise. For example, ladder agility drills, skipping, bounding and hopping adequately warms up the body while preparing the body for plyometric training. Never perform plyometric exercises on heavy lifting days since muscle fatigue may increase the potential for injuries to occur. Box jumps should not be performed if they displace the center of gravity more than eighteen inches for a two hundred pound athlete for safety concerns. Following these guidelines will ensure a safe environment for the athlete while performing plyometric exercises and assist in preventing injuries.

Another important concept to understand is the progression of plyometric training. The proper progression of plyometric exercise will maintain proper body mechanics, increase body awareness and prevent injuries. Plyometric training utilizes foot strikes (fs) to measure the amount volume per exercise. Generally three sets of foot strikes are performed for each exercise. The typical volume of exercises is generally recommended: beginners 50-100 fs, intermediate athletes 100-200 fs and advanced athletes 200-400 fs. On the other hand, the intensity level of the exercise inversely affects the level volume; the greater the intensity signifies a decrease in volume. Allowing adequate rest cycles between sets is necessary for the athlete to perform plyometric exercises at maximal intensities; however, this is a subjective measurement and usually ranges between thirty seconds and three minutes. Plyometric training should always begin with low intensity exercises while gradually increasing to high intensity exercises so proper body mechanics are maintained to avoid injuries. The recommended progression for plyometric exercise is as follows: standing vertical jumps, standing horizontal jumps, standing lateral jumps, multiple jumps, bounding, box jumps and depth jumps. Lastly, provide appropriate recovery time, generally forty-eight to seventy-two hours or merely perform plyometric training once a week.

In conclusion, plyometric exercise is an effective tool to increase power, resulting in enhanced athletic performance. The stretch reflex model and the mechanical model explain the physiology of plyometric exercise and demonstrates how the athlete achieves increased power production during training. The three phases of plyometric training provide the essential components necessary during plyometric exercise in order to experience increased power, resulting in enhanced performance levels. By adhering to the safety guidelines while performing plyometric exercises the athlete will be in a safe environment that will decrease the chance of injury. Progressing the athlete through pylometric training is an essential aspect that will further increase sport enhancement if conducted in a safe and logical manner. Plyometric exercise provides the results that athletes are searching for in order to be successful during competition.

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