Plyometrics is the term given to exercises designed to increase the power of an athlete. It is defined as the equivalent of explosive strength (Brukner and Khan 2001) and referred to by others as “speed-strength” (Young and Bilby 1993). In layman’s terms, the aim of plyometrics is to increase the explosiveness of the muscle allowing an athlete to run faster, jump further, or generate force at a greater rate.
This type of training aims to produce a large and rapid stretch of the muscles being trained during the eccentric phase immediately prior to the concentric phase of the exercise (McArdle, Katch, and Katch 2001). A practical example of this action is when an athlete performs depth jumps.
The athlete jumps from a raised platform. As the athlete’s feet hit the ground and he or she descends into a semi-squat position, the quadriceps muscles are rapidly lengthened. This is referred to as the pre-stretch, which generates a large stretch (myotatic) reflex (McArdle, Katch, and Katch 2001).
The athlete jumps vertically as high as possible aided by the large concentric contraction of the muscles as a result of the stretch reflex. The increased size of the muscle contractions is due to two key factors—increased elastic potential energy prior to the concentric contraction and stretch-induced reflexes resulting in greater muscle activation (McArdle, Katch, and Katch 2001).
Hence, plyometric training takes advantage of the stretch-shortening cycle (SSC), which is present in many sports-specific actions to increase the amount of force an athlete can produce in a given timeframe. This equates to the power produced by that athlete. So, in theory, an athlete should become more powerful and faster through adaptation to sports-specific plyometric exercises. But does this work in practice?
McArdle and colleagues (2001) state, “Testimonials abound about the benefits of plyometric training, but such pronouncements cannot substitute for the lack of carefully controlled evaluations of both benefits and possible orthopedic risks.” In contrast to this, the “Explosive Plyometric Exercise” position paper of the National Strength & Conditioning Association states that plyometric exercise programs “can improve performance in most competitive sports” and that properly applied plyometric programs are no more dangerous than other forms of training (National Strength and Conditioning Association).
In a study comparing maximal power training and a combined weights and plyometrics regime, it was found that both methods resulted in significant improvements in sports performance including sprint times over 20 meters and 40 meters (Lyttle, Wilson, Ostrowski 1996). The combined weights and plyometrics training program produced better results in the stretch-shorten cycle movements tested. This combined with Baker and Nance’s (1999) findings that 40-meter sprint performance could be predicted by an athlete’s power in SSC exercises suggests that there is value in utilizing this type of training for sprints of this distance.
Rimmer and Sleivert (2000) compared the effects of sprint-specific plyometric training against traditional sprint training on 10-meter and 40-meter sprint times. The plyometrics group showed significant decreases in both 10-meter and 40-meter times. However, these improvements weren’t significantly different from the sprint group. In their conclusion, the authors state that sprint-specific plyometrics can improve 40-meter sprint times by the same extent as traditional sprint training possibly through decreasing ground contact times.
Rimmer and Sleivert’s findings also supported an earlier study that showed plyometric-induced performance improvements were greatest over the initial acceleration phase of the first 10 meters (Delecluse, et al. 1995). In this study, it was found that the plyometric training group gained significant improvements in their 10-meter sprint times when compared to high resistance, sprint, and passive control groups. The plyometrics group also improved significantly in their 100-meter sprint times when compared to the sprint and passive groups.
It seems that the use of plyometric methods of training to increase speed is widely accepted and utilized by coaches and athletes. However, for all the anecdotal support, there are relatively few scientific studies cited in the literature that clearly define plyometrics as a viable mechanism for increasing speed. Given the limited findings in this area and the several research articles that suggest real benefits from plyometrics, it is clear that further well-controlled studies are needed to clarify the role of plyometrics in training for speed.
References
Baker D and Nance S (1999) The Relation Between Running Speed and Measures of Strength and Power in Professional Rugby League Players. Journal of Strength and Conditioning Research 13(3):230–235.
Brukner P and Khan K (2001) Clinical Sports Medicine, Second Edition. McGraw-Hill Book Co.: Sydney.
Delecluse C, Van Coppenolle H, Willems E, Leemputte M, Diels R, Goris M (1995) Influence of high-resistance and high-velocity training on sprint performance. Medicine and Science in Sports and Exercise 27:1203–09.
Lyttle AD, Wilson GJ, Ostrowski KJ (1996) Enhancing Performance: Maximal Power Versus Combined Weights and Plyometrics Training. Journal of Strength and Conditioning Research 10(3):173–79.
McArdle WD, Katch FI, Katch VL (2001) Exercise Physiology, Energy, Nutrition, and Human Performance, Fifth Edition. Lippincott Williams & Wilkins: Philadelphia.
National Strength and Conditioning Association. From: http://www.nsca-lift.org/Publications/posstatements.shtml#Plyometric. Accessed: August 4, 2006.
Rimmer E and Sleivert G (2000) Effects of a plyometrics intervention program on sprint performance. Journal of Strength and Conditioning Research 14(3):295–301.
Jumps, University of Oregon. From: http://www.uoregon.edu/~j15/jump/jump_index.htm. Accessed: August 4, 2006.
Young WB and Bilby GE (1993) The effect of voluntary effort to influence speed of contraction on strength, muscular power, and hypertrophy development. Journal of Strength Conditioning Research, 7:172.
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