Plyometric training has increased in use in recent years, primarily as a method of 'bridging the gap' between raw, maximal strength and power (Faccioni, 2001). However, it is by no means a new training modality (Chu & Plummer, 1984). The theory behind plyometric training is that the body utilises an 'arousal mechanism' which allows the athlete to make the most of the body's capacity (Chu, 1996). Plyometric training holds many benefits to almost any sport, as almost every sport requires athletes to be able to produce a maximal or near maximal effort as quickly as possible and as a result, the majority of the activities involved in plyometrics include hopping, jumping, skipping and throwing (Chu, 1996). Plyometric training can take many forms and be undertaken in a variety of methods and variations; however, all variations share a common goal, which is to increase muscular power. The basic principle behind any plyometric activity is a fast eccentric muscle action followed by a rapid concentric contraction, all based around a very short contact time (<0.2s). It is crucial at this point that it be noted that plyometric activities are not the same as ballistic exercises due to the contact time. It must be noted that plyometric training is not a replacement for existing training but simply a variation and it must be remembered that specificity is one of the key principles of training and studies have shown that the most effective plyometric training regimes are those that are specific to the sport in which they are being applied (Edwin & Gordon, 2000).
A plyometric training regime causes various physiological adaptations on the body to produce the desired effect. There are various studies showing that plyometric training increases muscular power (insert ref.), however, for coaches and sports scientists, it is crucial to understand the mechanisms behind this increase in power. Vissing et al. (2008) found that a plyometric training intervention increased the cross-sectional area (CSA) in upper leg muscles (quadriceps, hamstrings and adductors). This increase in CSA results in an increase in overall muscle fibres and MTU's and ultimately allows more muscle activation to produce more force. However, Vissing et al. (2008) also noted that during their study there was no significant change in fibre type as a result of plyometric training.
In terms, of motor unit adaptation; Motor unit (MU) synchronization is improved which means that multiple MU's can be recruited to ultimately improve speed of contraction as well as overall force of contraction. There is an increase in MU discharge rate, which means that MU's can be re-recruited faster resulting in faster repeated contractions, whilst golgi dis-inhibition means that the muscle can stretch much further and produce greater forces.
However, plyometric training is not specific to speed and power athletes, endurance athletes can also apply plyometric training to their training in order to improve running economy etc. Spurs, Murphy and Watsford (2003) found that plyometric training induced a 2.7% increase in 3km running performance, however the athletes showed no change in VO2 max or lactate threshold. Plyometric training was shown to increase musculotendinous system (MTS) stiffness which has been directly related to increased running economy, which therefore reduces the energy cost of distance running (Spurs, Murphy & Watsford, 2003; Saunders et al, 2006)
Training Techniques
Many athletes and coaches are often aware of various techniques to implement plyometrics into their training, but are often unaware of the variations of these exercises and the subsequent benefits to the variation.
Hurdles
Possibly the most common plyometric exercise given to an athlete, hurdles are ideal in that they can limit the ground contact time and have a large amount of scope for variation. Hurdles are beneficial in that they help to develop triple-flexion and triple-extension, two of the most fundamental aspects of almost every sport, as well as a rapid change between the two. Hurdles can be useful as they require no additional weight, reducing impact forces on joints, and can be adapted to suit the progression and ability of the athlete. Some examples of progressions can be; heights of hurdles, distance between hurdles, single-leg hurdles or a combination of these, the key characteristic of this activity is to maintain that short ground contact time of <0.2s to keep the hurdle plyometric.
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Jump Boxes
Jump boxes again offer an excellent range of diversity and progression whilst targeting key areas. An extra added benefit of jump boxes are that they require very little space to and are often easily transported, ideal for the coach or athlete with limited facilities. They are useful in that they can once again work the triple-flexion and triple-extension principles as well as working the stretch-shortening cycle (SSC). The use of jump boxes can be changed to make the exercise more difficult, such as increasing the height of the jump box. Also, different benefits will be observed by jumping onto a jump box as opposed to completing drop jumps.
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Medicine Ball Throws
Medicine ball throws are not necessarily plyometric in nature however they are a great exercise for developing upper body power, which is significant to most sports people. Although medicine ball exercises usually don't require tremendous amounts of space, therefore making them a practical power exercise for most athletes. they are also useful for sports teams, as often, permitting the coach has several medicine balls, exercise can be (and sometimes must be) completed in groups. The main method of modification for this exercise is by varying the weight of the medicine ball, however, the distance between the thrower and the target also manipulate training as, by increasing the distance means that the athlete must increase the force to cover it.
Again, these are not strictly a plyometric exercise, however, very few purely plyometric exercises exist for the upper body. It is known that push-ups are a useful and practical method of increasing 'strength', however in order to increase power, a speed element must be added (power = speed x strength). It is for this reason that a 'plyometric' push-up can be used to develop power. This exercise is fairly limited in terms of adaptation and variation, however, adding weight to the athlete (either naturally or via means of a weighted jacket), requiring higher force generation by the athlete. Although they are not necessarily plyometric, Vossen et al (2000) found that a plyometric push-up training regime, demonstrated higher improvements in power than a dynamic/regular push-up training programme.
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Exercise Prescription and Programme DesignPlyometric exercise is easily modified and adapted to suit a wide and varied array of clients. Exercises can be made more simple/complex and easier or more difficult depending upon the needs of the athlete.
There are many factors effecting the intensity at which a plyometric training session can be set at.
The volume of exercise, any load or weight added to the athlete, exercise complexity and session duration all must be taken into account when planning plyometric training. If these are too high, exercises can be more ballistic than plyometric and the 'speed' component of the exercise will be lost (remember that power = strength x speed).
Also, the abilities of the athlete should be taken into account, if the athlete is not strong enough or lacks the basic technique for example, it may result in serious injury of the athlete which will delay overall training. Equipment is also a big health and safety issue when conducting a plyometric training programme. Making sure the athlete is training on a non-slip surface, for example, would help to reduce the risk of injury as well as making sure the athlete has appropriate footwear. This helps by, again reducing the risk of slipping and also reduces the impact forces, minimising the risk of joint injury.
References
Chu, D.A. (1996) Explosive power and strength: complex training for maximum results. 1st edn. USA: Versa Press.
Chu, D.A. & Plummer, L. (1984) 'The language of plyometrics', Strength and Conditioning Journal, 6(5), pp. 30-31. [Online.] Available at: http://journals.lww.com/nsca-scj/Citation/1984/10000/The_language_of_plyometrics.5.aspx (Accessed 03 May 2012)
Edwin, R. & Gordon, S. (2000) 'Effects of a plyometric intervention programme on sprint performance', The Journal of Strength and Conditioning Research, 14(3), pp. 295-301. [Online.] Available at: http://journals.lww.com/nsca-jscr/Abstract/2000/08000/Effects_of_a_Plyometrics_Intervention_Program_on.9.aspx (Accessed 02 May 2012)
Faccioni, A. (2001) 'Plyometrics' [Online.] Available at: http://163.178.103.176/fisiologia/general/activ_bas_3/Plyometric1.pdf (Accessed 01 May 2012)
Men's Health (2012) 14 Smart Push-up Improvements. Available at: http://www.menshealth.com/mhlists/pushup-variations/plyometric-pushup.php (Accessed 07 May 2012)
My vegan weight-loss journey (2012) My personal journey of becoming a healthy vegan. Available at: http://myveganweightlossjourney.blogspot.co.uk/2012_02_01_archive.html (Accessed 07 May 2012)
Top wide reciever training (2012) Plyometric Drills - Part 1. Available at: http://www.top-wide-receiver-training.com/plyometric-drills.html (Accessed 03 May 2012)
Saunders, P.U., Telford, R.D., Pyne, D.B., Peltola, E.M., Cunningham, R.B., Gore, C.J. & Hawley, J.A. (2006) 'Short-term plyometric training improves running economy in highly trained middle and long distance runners', Journal of Strength and Conditioning Research, 20(4), pp. 947-954. [Online.] Available at: http://journals.lww.com/nsca-jscr/Abstract/2006/11000/Short_Term_Plyometric_Training_Improves_Running.36.aspx (Accessed: 07 May 2012)
Spurs, R.W., Murphy, A.J. & Watsford, M.L.(2003) 'The effect of plyometric training on distance running', The European Journal of Applied Physiology, 89(1), pp. 1-7. [Online.] Available at:
http://www.springerlink.com/content/f2jca5m77nq1mwev/ (Accessed 03 May 2012)
Vissing, K., Brink, M., Lonbro, S., Sorenses, H. & Overgaard, K. (2008) 'Muscle adaptations to plyometric vs. resistance training in untrained young men', Journal of Strength and Conditioning Research, 22(6), pp. 1799-1810. [Online.] Available at: http://jr3tv3gd5w.scholar.serialssolutions.com/?sid=google&auinit=K&aulast=Vissing&atitle=Muscle+adaptations+to+plyometric+vs.+resistance+training+in+untrained+young+men&id=doi:10.1519/JSC.0b013e318185f673&title=Journal+of+strength+and+conditioning+research&volume=22&issue=6&date=2008&spage=1799&issn=1064-8011 (Accessed 03 May 2012)
Vossen, J.F., Kramer, J.F., Burke, D.G. & Vossen, D.P. (2000) 'Comparison of dynamic push-up training and plyometric push-up training on upper-body power and strength, Journal of Strength and Conditioning Research, 14(3), pp. 248-253. [Online.] Available at: http://people.stfx.ca/jvossen/Pubs/Plyopu.pdf (Accessed 07 May 2012)
