Plyometrics
Related Terms
Plyometric exercises, power training, stretch reflex, stretch-shortening cycle.
Background
Plyometric exercises are specialized and very intense training techniques, which are used to develop muscular power, referring to the relationship between strength and speed. Plyometrics include any exercise where the muscle is contracted eccentrically (stretched) then immediately moved concentrically (contracted). The ability to generate a force in a short time allows for athletic movements beyond what strength alone will allow. For a muscle to cause movement, it contracts concentrically. Various muscles have different maximum amounts of power with which they can contract. However, if the muscle is lengthened (eccentric contraction) just prior to the contraction, it will actually produce more power. In order to produce this effect, the time between the eccentric contraction and the concentric contraction must be very short.
An example of a plyometric exercise is push-ups with a clap in between each push-up. In this case, the pectoral muscles are elongated and loaded by the downward force of your body, stretching eccentrically, then immediately contracted to push the body back up, stretching concentrically. The clap push-up, as opposed to a normal push-up, ensures that there is only a short amount of time between the eccentric and concentric contractions of the muscle. Examples of lower body plyometrics include depth jumps, multiple jumps, marches and lateral jumps, often involving boxes or platforms, and weight vests. Mid-section plyometrics include the broomstick twist, and twists, side-throws and sit-ups using a medicine ball. Upper body plyometrics involve medicine ball exercises and different types of push-ups.
The word "plyometrics" has been around since the 1960s but athletes were using the technique many years before the term was coined. Some of the exercises commonly used today include jumping off a box and rebounding off the floor onto another, higher box while either carrying weights, or more often wearing a weight vest.
While plyometrics have been shown to increase power, experts' opinions vary regarding the safety of these exercises. Many well-respected fitness experts argue the benefits and effectiveness of plyometric exercise. However, there are others who strongly deny these benefits and argue that plyometric exercises are extremely unsafe and the risk of injury far outweighs any potential benefits. Most experts state that a thorough grounding in weight-training is essential before starting plyometrics.
Theory / Evidence
The underlying principle of plyometric training is the stretch-shortening cycle. As a muscle stretches and contracts eccentrically, it lengthens while it contracts and produces storable elastic energy. If the muscle then contracts concentrically, shortening while it contracts, this stored elastic energy can be used to increase the force of the contraction. Therefore, a muscle stretched before it contracts will contract much more forcefully. Plyometric training places increased stretch loads on the working muscles. As the muscles become more tolerant to the increased loads the stretch-shortening cycle becomes more efficient, meaning the muscle stores more elastic energy. It can transfer from the eccentric or stretching phase to the concentric or lengthening phase more rapidly, thus generating peak power. These types of exercises can be used in many different sports training, for example, to improve a boxer's punch, or increase a basketball player's vertical jump.
While many well respected fitness experts argue the benefits and effectiveness of plyometric exercise, others strongly deny these benefits and dispute that plyometric exercises are exceedingly unsafe and the risk of injury far outweighs any potential benefits.
Based on one study, plyometric exercises may increase peak bone mass in adolescent girls as compared to girls who are not undergoing plyometric training after a period of nine months. The plyometric exercises used in this study include squats, lunges and calf raises using weighted vests, and hopping, bounding and box depth jumps. More high-quality studies are needed to draw any firm conclusions.
Author information
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
Bibliography
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Technique
A thorough warm up is recommended prior to plyometric training. This typically includes jogging, stretching, striding and general mobility especially about the joints involved in the planned plyometric session. A cool down usually follows each session.
For bounding exercises, surfaces such as grass or resilient surfaces are used. Cement floors are usually avoided due to lack of cushioning. Individuals use well-cushioned shoes that are stable and can absorb some of the inevitable impact. All athletes should undergo general orthopedic screening before engaging in plyometric training.
Physical educators have long used various plyometric apparatus-including medicine balls, jump ropes, and Indian clubs. One plyometric exercise involves catching and tossing a medicine ball to an assistant while the exerciser lies on his back. The triceps and chest muscles work both while they are lengthening (catch phase) and while contracting (toss phase).
The following are examples of plyometric exercises:
Bounding and hurdling: This is a form of plyometric training, where over sized strides are used in the running action and extra time spent in the air. Two-legged bounds reduce the impact to be endured, but to increase the intensity one legged bounding, or hopping, can be used. Bounding upstairs is a useful way to work on both the vertical and horizontal aspects of the running action. Multiple jumps over a series of obstacles like hurdles may be valuable drills for athletes training for sprinting or jumping events.
Drop jumping: This exercise involves the athlete dropping (not jumping) to the ground from a raised platform or box, and then immediately jumping back onto the platform. The drop down gives the pre-stretch to the leg muscles and the vigorous drive upwards the secondary concentric contraction. The exercise will be more effective the shorter the time the feet are in contact with the ground. The height of the drop is usually in the region of 30 to 80 cm. Drop jumping is a relatively high impact form of plyometric training and would normally be introduced after the athlete had become accustomed to lower impact alternatives, such as two-footed jumping on the spot.
Medicine ball: This involves a person lying on the ground face up. A partner then drops a medicine ball down towards the chest of the athlete, who catches the ball (pre-stretch) and immediately throws it back.
Press ups & hand clap: Press-ups with a hand clap in between is a particularly vigorous way to condition the arms and chest. The pre-stretch takes place as the hands arrive back on the ground and the chest sinks, and this is followed quickly by the explosive upwards action. The time in contact with the ground should be kept to a minimum.