Introduction

The popularity of the training method commonly known as ‘plyometric training’ is evident in nearly all sports, and at all levels of competition today.  We have travelled from a time during the seventies and early eighties of limited awareness and open scepticism, to a time during the late eighties and early nineties where athletes and coaches in all sports are influenced to believe that if plyometric training is not part of their training methods, they are missing out.

What is plyometrics?

The term ‘plyometric’ is commonly believed to be derived from Greek words meaning respectively “greater, longer, wider” and “to measure, to appraise, to compare” (Wilt, 1975; Duda, 1988; Zanon, 1989).  Exercises considered to be plyometric in nature include movements where a rapid eccentric (pre-stretch) contraction is followed immediately by a quick concentric contraction.  Other terms used to describe this type of exercise include jump training, depth jump training, drop jump training, stretch-shortening training, reactive training, eccentric-concentric training (Reid, 1989); “bounce” training (Lundin, 1986; 1991); and stretch-shortening drills (Steben and Steben, 1981).

However, based on my conclusions, the term ‘stretch-shortening cycle’ (SSC) is possibly the most appropriate to use in any description of ‘plyometric’ exercises.  The stretch-shortening cycle is a naturally occurring biological phenomenon where a concentric (muscle shortening) contraction is preceded immediately by an eccentric contraction.  The concentric power (force available when the muscles are shortening) is enhanced or augmented because of the prior eccentric (when the muscles are lengthening) contraction.  The aim of plyometric training is to enhance the expression of speed and/or power during a stretch-shortening cycle.   Therefore, the term stretch-shortening cycle can be used as a synonym for plyometric training – a movement consisting of an eccentric muscular action followed by a concentric muscular action.

The history of plyometric training

Plyometric training in the 1980’s was often referred to as a new, revolutionary form of training (Gambetta, 1981; Hagerman, 1986).  Whilst this form of training may have been new to many Western world countries, they had been included in the training of certain countries (e.g., the Soviet Union) since the 1960’s – over thirty years ago (Tabachnik, 1990).  In reality, athletes throughout history modeling their sport in training have been using plyometrics e.g., Arthur Lydiard in the 1950’s made use of bounding type exercises to develop a powerful stride (Hennessy, 1990).  When coaches see drills such as tuck jumps being defined as plyometric training, invariably their response is ‘We have been doing that for years!’  The inference here is that it is the formalization and organization of the training method known as plyometric training rather than the exercises themselves which may be ‘new’.

The term plyometrics first appeared in the literature of sports methodology in 1966, in a Soviet publication (Zanon, 1989).  Most of the early writings focused on depth jumps.

Possible further confusion in literature and training resulted from the misinterpretation of some of the early work on plyometric training which centered almost exclusively on the depth jump.  Depth jumping became synonymous with plyometric training, resulting in the exclusion of many other valuable plyometric training options.  Additionally, the heights used in the depth jumps as claimed in early literature were literally applied to athletes of all types and stages of development.  Resultant injuries further delayed the acceptance of plyometric training, reflected in comments such as the following by Adams (1987): “… plyometrics have the greatest injury potential of any single training method.”

How do plyometrics work?

The basis of plyometric training is to train the stretch-shortening cycle.  The rationale behind the use of the stretch-shortening cycle is that it augments the concentric phase of movement, resulting in an increase in work and power generated (Asmussen, and Bonde-Peterson, 1974a; Bosco, and Komi, 1979a; and Cavagna, et al., 1968) or enhances the efficiency (energy cost) of movement when compared with similar movements performed without the prior stretch (Cavagna  et al., 1964; Thys et al., 1972; Asmussen, and Bonde-Peterson, 1974b).

What factors influence the SSC?

The extent to which the stretch-shortening cycle influences the power output in any given movement is determined by a number of factors, including:

• The rate of the eccentric contraction.
• The length of the delay (coupling time).
• The rate of the concentric contraction.
• The external load.

The factors that appear to influence the SSC ability of the athlete include:

• Fiber type.
• Strength.
• Movement background.
• Age.
• Gender.

What training does the stretch-shortening cycle apply to?

Traditionally the only recognition of the stretch-shortening cycle has occurred in the speed-strength classification of reactive (or elastic) strength.  Applying the broader awareness presented in this article, it is important to recognize the involvement of the stretch-shortening cycle in all strength qualities (see Fig 1).  The training implication here is once the involvement of the SSC is recognized as contributing to all qualities, many possibilities exist to manipulate this component to contribute to elevated performances.  Specifically, periodization of the stretch-shortening cycle is an important possibility.

 

Contribution of the SSC to power output

LOW                                                                                    HIGH

_____________________________________________________

Maximal strength                                                      Speed strength

Strength Qualities

Fig 1 – The relationship between the strength qualities and the contribution of the SSC to power output.

Many coaches and athletes associate plyometric training only with speed or strength training.  The potential role of the SSC in the training of endurance and other strength sub-qualities (e.g., maximal strength training and hypertrophy) is often overlooked.

How does specificity affect plyometric training?

The principle of specificity supports the application of plyometric training.  The laws of specificity may suggest that in order to be most effective, plyometric training should exhibit similar patterns of 1) motor unit recruitment; 2) temporal sequence, and 3) firing frequency to movements in the events (Bosco, 1985).

Plyometric program design decisions

The athlete and/or coach are faced with making several important decisions with respect to:

• How much should the athlete train the maximal strength, and how much should the athlete train the stretch-shortening cycle?
• From an annual periodization perspective, in what order to develop each; and what kind of progression should the training load follow?
• How to include plyometric training in conjunction with energy system training, technical and tactical training?
• From a multi-year periodization perspective, in what order to develop?

Is plyometric training for everyone?

Due to the increased awareness and popularity of plyometrics, and the fact that minimal equipment is required, it is now common to observe coaches at all levels implement frequent and sometimes extensive plyometric training with athletes at early stages of development and continue attempting to elicit long term changes in the elastic strength, often without prior attempts to elicit significant gains in maximal strength through conventional methods.

The final decisions in program design should be influenced by the athlete’s response to the training process.  Keep in mind the steps involved.  Plan, implement, assess, revise, plan etc.

Conclusion

The early awe of plyometrics may have dimmed, some questions may have been answered.  After all, history suggests that this method (in its formal sense) is some 55 years old, and in reality, as old as physical training itself.  But is it really fully understood?  Is it really being utilized or exploited to its potential?

I doubt it.  I believe that the information contained in my book Understanding Plyometrics will be of great value to those who take the time and make the effort to read it.  This book aims to place plyometrics in perspective, to guide the athlete and coach in their understanding of this training method.

Many people want the quick solutions – which exercises and how many of them.  Many authors are keen to oblige.  The result – there are tables listing or categorizing plyometric exercises as ‘beginner, intermediate or advanced’; there are tables which show how many repetitions are appropriate at these beginner, intermediate and advanced levels.  These tables are based on individuals or collections of individuals opinions.  But of greater importance is that they are generalizations.  If you are happy to train or train others along ‘generalizations’, these tables will meet your needs.

But if generalizations are not good enough, you need to know more.  You need to know how to determine whether an exercise is basic or advanced – based on the capabilities of the individual – not on how some categorize the exercise.  Take hopscotch for example – it would fall into most existing tables under the ‘beginner’ column.  But to an individual with osteoarthritis in the knee, or who recently had lower body surgery – would it be a beginner exercise?  Probably not.  Most likely it would be too advanced!  The exercise should not be classified – the exercise needs to be matched to a level of ability to determine its appropriateness.

The book Understanding Plyometrics aims to increase your understanding of plyometric training and to improve your ability to apply safely and effectively what some call plyometric exercises to your training program, or to the training program of the athletes you train.

Perhaps the most important aspect of this book about plyometric training is the presentation of plyometrics as an integral part of almost all training movements, as opposed to the presentation of plyometrics as a separate, sometimes mystical, often commercialized, training method that will do all things to all athletes at any given time.

This revised or alternative perspective of plyometric training places the role of the stretch-shortening cycle and the training benefits of stretch-shortening cycle drills in perspective – in the continuum of training.  This may vary from what developed in the western world during the 1980’s.  This early western world perception which can be described as ‘classical plyometrics’ influenced a narrow perception of what constituted the training of the stretch-shortening cycle and separated it from other types of training.