By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Plyometrics is a conditioning technique used to increase performance in sports, according to the National Academy of Sports Medicine. It is particularly useful for sports that require explosive speed, power, and agility, such as Alpine skiing, soccer, and sprinting.
What Are Plyometrics?
The term “plyometrics” was first coined in 1975 by Purdue University’s Fred Wilt, who coached the women’s track team. Wilt created the word by combining the Greek words “plythein” (to increase) and “metric” (to measure). Plyometrics strives to “increase the measurement” in athletic skills such as sprint speed, jump height, and throwing and serving velocity.
Also called bounce loading or rebound jumping, plyometrics implements a “cocking” action via a rapid stretching of a muscle group from an eccentric (lengthening) contraction to a concentric (shortening) contraction, according to Medical News Today. This muscular “cocking” is necessary to gain the maximum vertical height when a basketball player jumps upward to throw the ball toward a basket or the maximum arm speed when a baseball player throws a baseball. This quick stretch-shortening cycle is a major factor in many sporting events, and its importance in athletic training has long been underestimated.
How Plyometric Training Improves Athletic Performance
Sport Fitness Advisor notes that the physiology behind plyometric training is that a muscle that is contracted immediately after being stretched will produce greater force than a muscle that has not been pre-stretched. The faster a muscle is allowed to shorten during pre-stretch, the greater the tension it can exert.
Additionally, the less the amount of time that a muscle spends in the pre-stretch position, the greater the acceleration. Receptors within the muscles called muscle spindles react to a sudden pre-stretch by sending nerve signals to the spinal cord.
Milliseconds later, these nerve signals result in a reflex contraction of the same muscle fibers that were stretched. According to Coaches Education, plyometrics “fools” this natural defense mechanism against injury, known as the “myotatic stretch reflex,” to enhance muscular force generation.
Plyometric training also utilizes the natural elastic recoil energy stored within the muscles to increase strength, notes Science for Sport. An intricate elastic structure within and surrounding the muscles provides stability and integrity within each muscle fiber.
During plyometric training, these elastic elements act like a rubber band that has been stretched and suddenly released. The force generated during the eccentric muscle contraction is converted into an equal and opposite force during the concentric contraction. Over time, an athlete experiences gains in joint range of motion and flexibility as these elasticity properties develop.
Another advantage of plyometrics is that the central and peripheral nervous systems are trained to react with maximum speed, stimulating the muscles to shorten rapidly and produce maximum force, according to Dr. John Rusin. A skeletal muscle fiber must be innervated by a motor neuron in order to contract. Further research is being conducted regarding the importance of neural conditioning through plyometrics along with an evaluation of different neural training methods according to the National Academy of Sports Medicine.
Workout machines such as Nautilus® exercise and stair-climber machines provide great muscular workouts, but they only provide minimal neural training because of the muscles’ slow contraction speed. The level of neuromuscular training needed to improve coordination in most sports can only occur when the muscle is stretched rapidly and with large amounts of force.
Researchers have noted that athletes who have a genetically determined high percentage of fast-twitch muscle fibers will benefit more from plyometrics than athletes with more slow-twitch fibers. Fast-twitch muscle fibers are fast-contracting, require anaerobic (without oxygen) energy metabolism of carbohydrates, and are activated during speed and power movements. By contrast, slow-twitch fibers generate energy aerobically (with oxygen), can utilize both carbohydrate and fat, and are used to sustain continuous endurance activities.
Plyometrics training predominantly trains fast-twitch muscle fibers. As a result, this type of training is only advantageous when an athlete is training for fast-twitch activities, such as sprinting and alpine skiing.
RELATED: Alpine Skiing: The Use of Periodization Strength Training
Probably the most popular form of plyometrics is depth jumping, according to Sports Performance Bulletin. This exercise involves an athlete jumping from an elevated surface such as a bench or a box, landing simultaneously on the floor with both feet, immediately performing a vertical jump from the floor after the landing, and repeating the exercise for several repetitions.
The load on the athlete’s body can be varied by having the athlete jump off platforms of different heights and attaching weight belts to the body. Plyometric training can also be manipulated by varying the number of sets per session, the number of repetitions, and the frequency of workouts (although no more than two plyometric workouts per week are advisable).
Other variations of lower body plyometrics include lateral jumping over boxes (to simulate skiing gates during alpine skiing), double and single leg tucks, hopping/skipping takeoffs on one or both feet, and bounding in long, loping strides, according to The Conversation. Depth jumps should be performed on soft surfaces (mats or grass) to minimize shock, and they should be conducted within the mechanical action of the sport-specific range of motion for which the athlete is training.
A 10- to 12-pound medicine ball is commonly used in upper-body plyometrics, according to Stack. This type of ball can be used for throwing, catching and rotational exercises for the trunk and abdomen.
Plyometrics are predominantly conducted during the peaking phase of periodization training, immediately before a competitive season, according to researchers. Depth jumping, considered the most dangerous plyometric exercise, should not be used throughout the entire year because of the potential for injury and especially not when athletes are just beginning a strength training program.
During plyometric training, coaches should monitor athletes on an individual basis. This oversight will protect athletes from overuse injuries, such as tendinitis.
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Plyometrics Should Supplement Other Athletic Conditioning
Human Kinetics says that plyometrics should be not used in place of other training but should be used to supplement overall sport-specific conditioning involving periodization weight training and interval sprint training. Some coaches have recommended that an athlete build up enough strength to squat double their body weight before starting lower-body plyometric training. Ideally, athletes should start with elementary drills, such as skipping and hopping, before they advance to depth jumps and more advanced exercises.
Ultimately, all of the movements used in sports depend on an athlete’s ability to overcome the inertia of his/her own body weight or an external object. Plyometric training utilizes the athlete’s body weight, the force of gravity (depth jumps) or a weighted object (medicine ball drills) to increase muscular speed and strength for athletic activities. In competitive sports where an athlete’s win or loss can depend on mere seconds, more speed and strength as the result of plyometric training can be extremely helpful.
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