- Since Jumping Into Plyometrics was first published in 1992, there has been a virtual explosion in the number of trainers and coaches who embrace plyometric training as an integral part of their athletes’ development. Originating from track and field, this system of exercise has grown from mysterious to commonplace, while the end user’s knowledge of these exercises has grown dramatically. Even sports such as synchronized swimming credit plyometrics for raising the level of performance.
- Training with plyometrics exercise can help athletes capitalize on the synergistic effects of each muscle action.
- The largest forces that muscles are capable of producing occur when an external force exceeds that produced by the muscle, and the muscle is forced to lengthen. This is known as an eccentric action or “negative work.” When an athlete is running or jumping, they depend on eccentric actions of the lower extremities to dampen the forces when the body makes contact with the ground. If it were not for eccentric actions decelerating the body, one would collapse to the ground every time there is foot contact.
- Eccentric muscle actions are particularly useful to include in a training program of strength development. Since eccentric actions have the unique ability to develop much greater forces, they provide greater overload to the muscle as opposed to emphasizing only concentric actions. This can have a very important role in preventing muscle wasting as seen with aging or atrophy as a result of recovery from injury or surgery.
- The increase of bone muscle mass is directly related to the magnitude of muscle forces and other loads (body weight) on bone. Therefore the strength and density of bone are influenced positively when muscle strength is developed during resistance training and eventually by plyometric training.
- It is common knowledge among weightlifters that performing isometric actions can help train the muscle to deal with that specific angle or point in the range and thus increase the capability of moving the weight through that point. This fits in with the research that indicates that isometric strength is developed at specific points in the joints range of motion and if other points are ignored, strength in those areas will not be developed.Relative to plyometric training, specific exercise training techniques can be employed to focus on improving the isometric strength.
- The brief period of static “hold” as the body switches from eccentric to static muscle actions is known in plyometric language as the “amortization phase.” This time phase is brief indeed, less than .01 seconds in power-oriented athletes like jumpers and sprinters. The ability to rapidly switch from an eccentric action to a concentric contracting phase is the hallmark of good athletes. The one thing we know about good athletes in general is that they don’t spend a long time on the ground when running or jumping. These relatively brief ground contact times are directly related to the amortization phase of the athletes’ movements.
- An entire system of exercise—plyometrics—has arisen just to address the development of a shorter amortization phase. And, perhaps surprisingly, the length of the amortization phase is largely dependent on learning. Where strength and innate speed are important, an athlete can shorten the amortization phase by applying learning and skill training to a base of strength development.
- Research has indicated that heavy lifting and plyometrics as methods of training have effectively improved power output. This led to thinking that a combination of both systems could result in even greater improvements. This has proven to be so, particularly in the area of vertical jumping.
- Vertical jumping is a component of most sport activities. It is often taken for granted that an athlete instinctually knows how to jump vertically. In actuality, jumping vertically is a skill that can and should be taught to athletes.
- Plyometric exercises, even at low-intensities, can expose joints to substantial forces and movement speeds and are not appropriate for an athlete who does not maintain sufficient neuromuscular control to generate and attenuate high impulse joint loads. Before initiating dynamic lower extremity plyometric exercise, athletes should first be able to demonstrate a bodyweight squat with good posture, limited forward trunk lean and maintain neutral knee alignment; otherwise, these functional deficits are likely to be exacerbated when plyometric exercise is implemented due to the high forces.
- Guidelines for initiating plyometric exercise are poorly developed. Most of the criteria have been established on old literature based on high-intensity exercise (shock training) and is grounded in opinion rather than research. These guidelines may exclude a majority of female athletes and many younger athletes from participating in plyometric exercise even though these same athletes would be allowed to participate in competitive sports whose activities induce ground reaction forces five to seven times body mass.
- Plyometric training should be considered in the context of the athlete’s age, skill levels, injury history, and a myriad of other variables that comprise his or her athletic development.
Source: Plyometrics (Human Kinetics, 2013)
*Over the past 20 years, how has plyometrics changed in terms of acceptance by coaches, trainers, and athletes?
*What are the main sports that seem to benefit most from plyometrics raising the level of athletes’ performance?
*What are eccentric actions and how do athletes rely on these actions while they are running or jumping?
*Why are eccentric actions so important to include in a training program of strength development?
* How are the strength and density of bone influenced when muscle strength is developed during resistance training and eventually by plyometric training?
*What are isometric actions and how can specific exercise training techniques be employed to focus on improving isometric strength relative to plyometric training?
*What is the amortization phase and how does it relate to ground contact times seen in power-oriented athletes like jumpers and sprinters?
*How can athletes shorten the amortization phase and how does it differ from strength and innate speed?
*What led to the thinking that a combination of heavy lifting and plyometrics could help an athlete enjoy major improvements?
*Why has vertical jumping been taken for granted as something an athlete instinctually knows how to do, and why do you feel it is a skill that can and should be taught?
*What should athletes first be able to demonstrate before dynamic lower extremity plyometric exercise is initiated?
*Why have the traditional guidelines for determining when to initiate plyometric exercise often excluded most female athletes and the majority of younger athletes?
*When looking at someone’s athletic development, how should plyometric training be considered in the context of his or her age, skill level, injury history, and other variables?
To schedule an interview with Donald Chu and/or Gregory Myer, contact Maurey Williamson at 1-800-747-4457, ext. 7890, or firstname.lastname@example.org.
From Chapter 2 — "How Plyometrics Works"
Mechanics of Vertical Jumping
Vertical jumping is a component of most sport activities. It is often taken for granted that an athlete instinctually knows how to jump vertically. In actuality, jumping vertically is a skill that can and should be taught to athletes. If we examine the event a little more closely we find that the jump is preceded by a countermovement, in which the center of gravity (center of gravity) drops rapidly. This is seen as a flexing of the hips, knees, and ankles of the athlete. The trunk tilts slightly forward and the arms are pulled to a position behind the midline of the body.
Prior to the vertical movement of the body, there is a rapid extension of the hips, knees, and ankles, which is largely the result of force developed by the arms and legs. The arms should be brought forward rapidly and allowed to travel to a position above and in front of the shoulders. The quick bend of the knees which lowers the center of gravity is accompanied by moving the arms into a position where the shoulders are extended and the arms are behind the athlete. This position of the arms allows the athlete to develop force which is directed into the ground as the arms come forward.
Interestingly enough, once the arms pass the midline of the body they can no longer develop force that will help achieve overall height. Past this point they are only able to decelerate, and this allows the body to begin liftoff. Therefore, it is important to get the arms as far back and as straight as possible for maximum force development. The more the arms bend at the elbow the faster they will come through, but the less they will contribute to overall force development. A practical view of this is to compare the arm swing of elite triple jumpers versus that of elite high jumpers. Where maximum force is important for the triple jumper, high jumpers using the Flop technique must rely more on arm speed to effectively carry out their technique.
Research by Everett Harman, PhD, et al. (1991) at the U.S. Army Research Institute of Environmental Medicine has shown that the countermovement is crucial to development of force and can contribute up to six percent of the total jump height. The arms can increase the overall jump height attained by as much as 21 percent. It was concluded that the arms developed their positive effect by exerting downward force on the body as they swung through in the early phase of the jump and kept the body in a position such that the quadriceps and gluteus muscles could exert force over a longer period of time. It was also concluded that since the countermovement did not contribute that significantly to jump height, many sport situations may not require a large countermovement in order for the athlete to be effective. If speed of movement and reaction time is more crucial, such as in a volleyball block, the athlete may be just as effective by simply starting the jump with the knees bent. In other words, if an athlete does not need to attain maximum height a small-countermovement will clearly be the more effective technique.
Due to the arms’ large contribution to overall jump height it appears that strengthening these areas through resistance training exercises would be an important component of all jump training programs. Some of the exercises seen as important in the development of the arms for jumping include:
- Reverse Pull-Downs
- Triceps Dips
- Shoulder Swings
- Straight Arm Pull-Downs
- Seated Rows
- Backward Medicine Ball Throws
- Underhand Medicine Ball Throws
From Chapter 8 — "Introduction of a Plyometric Training Program"
Considerations for Program Design
A basic plyometric program might be intended for the novice or the young athlete. It should follow the rules of safety and the considerations set forth in chapter 4. If the program is intended for the more advanced athlete, the same rules apply, but the exercises become more complex and more intense. The following considerations affect the design of training programs at any level.
Teach beginners the concepts behind plyometric activities, including the importance of eccentric versus concentric strength. Stress the importance of the stretch-shortening cycle (the countermovement of the legs) in the ability to start quickly. Initial activities should be of lower intensity and preparatory in nature. The coach must be aware of the progression needed in both intensity and skill requirement.
Feet should be nearly flat in all landings. The ball of the foot may touch first, but the rest of the foot should also make contact. Landing should be reversed quickly; the object is to spend minimal time on the ground. For the arms to help develop force into the ground to “compress the spring,” elbows must be brought behind the midline of the body so the arms can be brought rapidly forward and up as the concentric contraction occurs for liftoff. This movement is the double arm swing.
The simple factor of attention span is probably the major consideration in starting youngsters in plyometric training programs. Children will always run and jump as a part of play. But as adults we tend to take this element of play (also known as fun!) out of training programs by rigidly applying specific regimens.
Elementary school children can successfully do plyometric training as long as the coach does not call it plyometrics. Children of this age need images, such as animals in the forest jumping over streams and logs, to relate to. They can visualize and cognitively grasp the ease and skill with which a deer bounds through the woods. If movement patterns are placed in the proper context, children can attempt to express them in a “plyometric” fashion. In fact, hopscotch is a great early plyometric drill!
Young athletes can benefit more from direct training as they approach pubescence. They can begin to relate more to sport situations and see the correlation between what the coach asks them to do and their development in their sport. Plyometrics for this group should always begin as gross motor activities of low intensity. They should be introduced into warm-ups and then added to sport-specific drills.
As athletes approach the stage of individualization, they can begin to look at developing off-season and preseason training programs as preparation for performance. For most athletes this will be upon reaching high school, although in certain activities (ice skating, gymnastics, swimming, diving, dance, and track and field) the coach and the athlete may need to begin developing training cycles that use regimented plyometrics at an earlier age. This also depends on the athlete’s level of competition.
Two considerations regarding training level are important when structuring a plyometric training program: the intensity level of the exercise and the experience of the athlete. Plyometric training should be a progression of exercises and skilled movements that are considered to be elementary, intermediate, and advanced in scope. They should focus on improving the ballistic and reactive skills of the exerciser and are to be considered stressful. Drills should be evaluated for intensity before they are incorporated into a workout. Categorizing exercises by intensity helps both in choosing starting points for exercise and in developing program progression.
Another factor in program design is the training experience of the athlete. The exercise must be geared to the individual. An athlete who is barely past pubescence and is relatively unskilled should be considered a beginner. Beginners should be placed in a complementary resistance training program and should progress slowly and deliberately into a program of low-intensity plyometrics such as skipping drills, 8-inch cone hops, and box drills from 6 to 12 inches.
High school competitors who have been exposed to weight training programs can benefit from moderately intense plyometrics. And accomplished, mature, college-level athletes with strong weight training backgrounds should be able to perform ballistic-reactive exercises of high intensity with no undue problems. Once a classification of beginner, intermediate, or advanced has been generally determined, one can begin to plan a program.
Time Frame or Cycle
After you have considered and assessed the athlete it is time to consider the program design points for a plyometric training program. One of the most difficult considerations for the coach of a good high school athlete is to find the time to insert a training program. Your best athletes are almost always multiple-sport athletes. They play one sport in the fall, have two weeks until they move to the winter sport and face the same situation as they move to spring activities.
Research has shown that physical development is best accomplished over a 4-6 week period. The whole theory of Periodization is one in which an athlete’s training year is divided into cycles or blocks of time with specific training goals and an attempt is made to re-assess whether or not the expected development has occurred.
Plyometric training, because of its ability to improve explosiveness and reactivity of muscles needs to be properly brought into the overall training program of the athlete. It should be used after a strength phase has been accomplished and gradually introduced to the athlete prior to the actual competitive season. Although some athletes such as jumpers in track and field will continue to do plyometric training throughout the season, backing off just before the Championship season, other athletes, such as Professional basketball players, would be foolish to attempt high levels of plyometric training during their season due to the tremendous workload of their competitive season.
The coach needs to look at the most opportune time to impose these types of activities. With the advent of year round competitive sports such as traveling soccer, basketball and volleyball programs, many of our athletes are going to miss a crucial part or time in their development. While “playing the game” may result in some physical development, the soft tissue system which is influenced by maturity and exposure to training stimulus may stagnate. It can be expected that an athlete may never reach their full potential if the opportunity to physically develop is not acknowledged.
It is in the best interest of all athletes to use off-court or field training not only for physical improvement but for recovery as well. The body reacts best when it is exposed to a variety of different stimuli. This has long been shown to be an essential part of the “General Adaptation Syndrome” described by Hans Selye many years ago when explaining an organism’s ability to function in any environment.
All of these considerations must be kept in mind when designing a program. That will help determine the types of exercise chosen, the appropriate level of intensity at which they are performed, the proper number of repetitions, and how frequently the athlete performs them.
From Chapter 3 — "Anatomy and Physiology of Plyometrics"
Defining Plyometric Exercise
Plyometric exercise is a popular form of training commonly used to improve athletic performance, which involves stretch of the muscle-tendon unit immediately followed by shortening of the muscle unit. This process of muscle lengthening followed by rapid shortening during the stretch-shortening cycle (SSC) is integral to plyometric exercise. The SSC process significantly enhances the ability of the muscle-tendon unit to produce maximal force in the shortest amount of time. These benefits have prompted the use of plyometric exercise as a bridge between pure strength and sports related power and speed.
Because the term plyometrics is a later creation in American literature, much of the early related physiological research is described by other names. The term used by researchers in Italy, Sweden, and the Soviet Union for this type of muscle action was the “stretch-shortening cycle.” As plyometric training techniques have evolved, its description and related terminology have undergone a metamorphosis. For example, based on origins from training described by Yuri Veroshansky, the Russian national jump coach for track & field, plyometrics were originally developed as “shock method” of training. Plyometric exercises can be described as activities that involve maximal effort, such as high intensity depth jumps. On the other hand, plyometric exercises have also been described as any movement, requiring either maximal or sub-maximal effort that involves the stretch-shortening cycle.
The terms “plyometrics” and “stretch-shortening cycle” are used synonymously by some authors; whereas others use the term “stretch-shortening cycle” in lieu of “plyometric” to differentiate from the literal translation of the Greek word “pliometric” (plio=more, plythein= increase, metric=measure) meaning “to increase the measurement.” The use of terminology often seems to differ by field of study. While the term “stretch-shortening cycle” is used in the physiology literature to describe activities such as running, jumping or throwing; the term “plyometric” is used in the rehabilitation and conditioning literature to describe these activities when they are used in training to capitalize on the SSC for maximizing force production or enhancing performance.
The term ‘amortization’ has been source of confusion when used to describe plyometric activity. Amortization means a “gradual extinction, extinguishing or deadening.” In reference to a depth jump, amortization has been described as the time from initial ground contact to reversal of motion, the time from initial ground contact to take-off (entire stretch-shortening cycle), and the transition between muscle lengthening and shortening. We will use and define the term “amortization” to describe transition between eccentric and concentric actions of antagonistic muscle groups which is synonymous with the coupling phase.
The focus and application of plyometric training has evolved in recent years. Often plyometric exercises in athletic conditioning programs are now performed at a sub-maximal level and are directed at the achievement of proper biomechanical technique and injury prevention in sport. Training in this manner has been effective in reducing lower extremity injuries as well as improving performance. Plyometric training has also crossed-over into the rehabilitation field. Recently published rehabilitation protocols include plyometric exercise as a means to improve function and facilitate a return to sport.
In this book, plyometric exercise is defined as activities that involve and capitalize on the mechanisms of the SSC to increase the efficiency of force production at a joint or increase performance. Simply stated, plyometrics are defined as exercises that enable a muscle to reach maximum strength in as short a time as possible. This speed-strength ability is known as power. Although most coaches and athletes know that power is the name of the game, few have understood the mechanics necessary to develop it.
To help you understand plyometrics, we will review the important points of muscle physiology. This will serve to demonstrate the simple, yet complex, way in which plyometric training relates to better performance.
Since the use of plyometric training in the development of an athlete’s athletic ability, there has been a great deal of effort expended on attempts to verify the effectiveness and safety of plyometrics. As might be expected, the results of these studies are mixed. Athletes of various sports and equally varied levels of conditioning have been compared to “untrained” athletes under all sorts of variables and conditions. The point that is missed in this research is that athletic development follows its own time curve. A 6-, 12-, or 24-week testing period can in no way reflect the longitudinal development that will occur throughout an athlete’s overall career. For some, this time span may be a single season, for others, it may be up to 30 years of highly competitive activity. Therefore, plyometric training should be considered in the context of the athlete’s age, skill levels, injury history, and a myriad of other variables that comprise his or her athletic development. In this way through applied research practitioners can learn to establish realistic expectations.