Introduction

Written in 1996, the objectives of this literature review were to give the reader a clear understanding of Plyometrics. Are plyometric exercises better than normal strength weight lifting programs? If Plyometric exercises are better than normal weight bearing exercises why aren’t they more popular? These are just two questions that will be answered by the end of this review and I’m sure it will answer many more as well.

Ploymetrics are commonly used to increase vertical leap, agility and power. When we talk about vertical leap, agility and power we are also talking about percentage of fast-twitch (F.T) muscle fibres. Plyometrics have been know to increase ones vertical leap by over 30cm under 6 months. Plyometric exercise is initiated when a muscle under goes a rapid stretch then is contracted powerfully causing the muscle to be put under great strain. Plyometric exercises aren’t suggested for people who haven’t done much weight or running fitness work before due to this great strain. Over training is also a good way to injure yourself as your body doesn’t have time to recover from the previous work out. Proper training techniques help avoid injury and also maximise the efficiency of the workout, therefore, being more beneficial.

Discussion

Plyometrics has become a training buzz word in the 90’s. Plyometrics have been around for many years originating from Russia and the Eastern Block countries. It was know in Russia as “jump training” or “shock training”. It wasn’t until the 60’s it got the name plyometrics from an American coach who felt that this type of training gave “measurable increases” in performance so he applied the Latin words “Ply” and “Metric” meaning respectively ‘increase’ and ‘metric’, giving Plyometric.

So what are Plyometrics?

Plyometrics refers to a type of intense training that maybe undertaken by an athlete who wants to improve speed, agility and power. This type of training also refers to very fast, explosive exercises (normally performed with body weight) to improve power out put and neural activation of the muscles (the ability for a muscle to contract quickly). Basically plyometrics relies on a element of physiology call the Stretch-Shorten cycle (SSC). This Stretch-Shorten cycle means that the muscle is rapidly stretched and then contracted which increases the force applied on the muscle.

Receptors within the muscle called muscle spindles react to this sudden stretching by sending a signal to the brain saying ‘this stretching is potentially dangerous’ then the brain contracts the muscle to stop the stretching. This serves to protect the stretch and protect against any possible injury. The pre-stretch is the SSC must be used by 0.2 of a second or other wise it’s lost. Generally plyometrics must be done with some type of bounce or any possible advantage gained by SSC is lost. So recapping, the SSC is initiated by the muscle spindles which detects a stretch and responds by causing the muscle to contract.

Plyometrics are beneficial to those who have a high percentage of fast-twitch (F.T) muscle fibres more so than those with a high percentage of slow-twitch (S.T) muscle fibres. F.T muscle fibres are those that contract quickly, require anaerobic (with out oxygen) energy metabolism of carbohydrate and are activated during speed and power activities. Where as S.T muscle fibres are completely the opposite. S.T muscle fibres gets its energy aerobically (with oxygen) , can use both carbohydrate and fat and is used in steady state endurance. There for plyometrics are only beneficial for training F.T muscles to compete in activities such as sprinting, shotput, ect… There are tests that may be done to determine your ratio of F.T to S.T muscle fibres but are costly and painful (muscle biopsy). You can normally make a good guess at what your percentage is, as if you’re a sprinter you would have a high amount of F.T muscle fibres. The percentage of F.T and S.T muscle fibres you have is genetic, supposedly meaning you either have a high amount of F.T or S.T muscle fibres and the majority of people would have about equal amounts of F.T and S.T muscle fibres.

From two main sources of information I have come to the conclusion that muscle fibres can be made by extreme training techniques. The book called Physical Education VCE Units 3 & 4 on page 364 states “The ratio of fast twitch to slow twitch fibres varies from individual to individual and muscle to muscle in the individual. This ratio is greatly inherited and cannot be changed by training.” Another abstract I received said; “These fibres (fast twitch and slow twitch) are influenced in a great way by specific training. In some cases there has been evidence of new fibres being created through very extreme training techniques.” From these abstracts you can make your own mind up but I believe that F.T muscle fibres are influenced by specific training and new fibers may only be made through extreme training techniques.

Probably the most popular plyometric exercise is depth jumping. Depth jumping is when as athlete jumps from an elevated platform, lands simultaneously with both feet, immediately performs a maximal vertical jump to the top of the platform and repeats for several repetitions. The load placed on the athletes legs can be changed by jumping of a platform at a different height or attaching weights to the body. This exercise may put up to 5-6 times body weight of stress on the tendons and ligaments there for it’s advised that no more than two plyometric workouts a week are needed. Due to this strain put on the body plyometrics are usually only conducted during the peaking phase of periodisation training (immediately prior to the competitive season). Also plyometrics shouldn’t be used in place of other training but should be used in conjunction with weight and interval sprint trainings. It’s advised by some coached that the athlete be able to squat 2 times there body weight before starting a plyometric jump program.

Plyometric jump programs have been proven to be most effective when weight training is under taken as well. Plyometrics is only dangerous when misused, when using the correct techniques and resting your body you shouldn’t receive any injuries from plyometrics.

Summary

Plyometrics is a type of high intensity exercise performed by athletes to inhance speed, agility and power. As these exercises exert much strain on the specific muscles it’s important to use the right technique and rest your body otherwise injury is prominent. Plyometrics have become the 90’s training buzz word. When incorporated into a periodised weight and sprint training huge improvements have be noticed in speed, agility and power. This type of training is mainly lower body orientated but there are also upper body exercises that may be done. I conclude that plyometrics and a weight program is the ideal way to increase ones vertical leap, as long as the plyometric exercises are performed properly.

References

1. “Physical Education VCE Units 3&4”, Robert Malpli, Margaret Horton and Glenn Davey. THOMAS NELSON AUSTRALIA, ’94.
2. “Physical Education: Theory and Practice”, Damien Davis, Tom Kimmet and Margaret Auty. MACMILLAN EDUCATION AUSTRALIA PTY LTD, ’95.
3. “Senior Physical Education: Book 2”, Sara Glover, Lisa Alexander, Julia Walsh. COGHILL PUBLISHING, ’93.
4. “Towards better coaching: The art and science of sports coaching:”, Editor: Frank S.Pyke.

Articles (URLs appear to be dead now)

1. “Plyometrics”, Lyle McDonald. (e-mail: [email protected]) World Wide Web site: “http://www.xnet.com/~schneid/vertical.html”
2. “Plyometrics revisited”, Lyle McDonald. (e-mail: [email protected]) World Wide Web site: “http://www.xnet.com/~schneid/vertical.html”
3. “Plyometrics III”, Lyle McDonald. (e-mail: [email protected]) World Wide Web site: “http://www.xnet.com/~schneid/vertical.html”
4. “Plyometrics”, Dan Graetzer World Wide Web site: “gopher://wilcox.umt.edu:70/00/UofM/hhp/plyo”
5. “Rolly’s Guide to jump training”,Rolly Keenan (e-mail: [email protected]) World Wide Web Site: “http://www.unt.edu/~rwk0001/jump.html”