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.

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.

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.

Safety

• Plyometrics has received much blame for overtraining and is thought to cause an increased risk of injury. Plyometrics, like other forms of fitness training, carries risks when used incorrectly and recklessly. The safety of plyometric exercises may depend on the frequency, length, and intensity of the exercises preformed. Consult with a qualified healthcare professional before making decisions about new exercise routines.

• Most experts believe that a solid strength base is required before starting a plyometrics program, meaning an individual should have the ability to squat at least twice their bodyweight or leg press at least 2.5 times their bodyweight. These basic requirements may help avoid injuries when starting a plyometrics program.

• It is not recommended that anyone under the age of 16 use plyometrics, particularly the more intense plyometric exercises, unless a fully qualified coach or physical trainer recommends otherwise. Because of the relatively immature bone structure in preadolescent and adolescent children the very great forces exerted during intensive depth jumps should be avoided.

• Particular injuries that may be associated with the high impact involved in plyometric training include but are not limited to back pain and injury, spinal shrinkage, heel-pad bruising, and patellar tendonitis (jumper's knee).

• Plyometric exercises should be performed on a soft surface such as grass or a synthetic running track.

• Two sessions of plyometrics per week is viewed as more than enough. A maximum of three sessions of plyometric exercises in a week should not be exceeded. It is important not to perform too many repetitions in any one session. The amount of repetitions performed should be based on a person's physical conditions and abilities.

• As with other exercises warming up is a crucial deterrent of injuries. It is recommended to spend 10 minutes of jogging or skipping followed by 5 to 10 minutes of stretching the muscles involved before the beginning of each plyometrics program. It is also important to remember to stretch the lower back.

Author Information

• This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

1. Behm DG, Wahl MJ, Button DC, et al. Relationship between hockey skating speed and selected performance measures. J Strength Cond Res. 2005 May;19(2):326-31. View Abstract

2. Besier TF, Lloyd DG, Ackland TR, et al. Anticipatory effects on knee joint loading during running and cutting maneuvers. Med Sci Sports Exerc. 2001 Jul;33(7):1176-81. View Abstract

3. Cossor JM, Blanksby BA, Elliott BC. The influence of plyometric training on the freestyle tumble turn. J Sci Med Sport. 1999 Jun;2(2):106-16. View Abstract

4. Fletcher IM, Hartwell M. Effect of an 8-week combined weights and plyometrics training program on golf drive performance. J Strength Cond Res. 2004 Feb;18(1):59-62. View Abstract

5. Martel GF, Harmer ML, Logan JM, et al. Aquatic plyometric training increases vertical jump in female volleyball players. Med Sci Sports Exerc. 2005 Oct;37(10):1814-9. View Abstract

6. Robinson LE, Devor ST, Merrick MA, et al. The effects of land vs. aquatic plyometrics on power, torque, velocity, and muscle soreness in women. J Strength Cond Res. 2004 Feb;18(1):84-91. View Abstract

7. Schulte-Edelmann JA, Davies GJ, Kernozek TW, et al. The effects of plyometric training of the posterior shoulder and elbow. J Strength Cond Res. 2005 Feb;19(1):129-34. View Abstract

8. Witzke KA, Snow CM. Effects of plyometric jump training on bone mass in adolescent girls. Med.Sci.Sports Exerc. 2000;32(6):1051-1057. View Abstract