[Julio is an Exercise Science graduate student at Old Dominion University and is an Athletic Development Intern at Athletic Lab]

When taking a look at the research, it is easy to conclude that the best speed-power athletes (think sprinters, long jumpers, Olympic Lifters, etc) are those who can produce the greatest amount of force in the shortest possible time (Young, 2007). Plyometric training is an excellent way to develop a muscle’s ability to generate explosive power, which is essential for improving agility, speed, and rate of force development and thus help enhance athletic performance.

Plyometric activities target the enhancement of the stretch shortening cycle (SSC). This is a combination of an eccentric and concentric contraction in a rapid succession that allows the integration of musculoskeletal phenomena such as the Golgi tendon organ (GTO) and muscle spindle to store elastic energy. In essence, a rapid stretch of the muscle or “eccentric phase” (i.e. the lowering phase of a squat) is followed by a rapid contraction or “concentric phase” (coming out of the bottom and exploding upwards). When the amortization phase, the time between eccentric and concentric phases, is kept to a minimum, the stored elastic energy is maximally used and allows for a much stronger concentric contraction of the muscle. This can lead to a higher force production and improved performance during jumps, throws, sprints, and lifts.

Another benefit of long-term plyometric training is Central Nervous System (CNS) inhibition. The high intensity nature of this type of training acclimates the CNS, causing it to progressively disengage these governors (GTOs and muscle spindles) the body normally would use to avoid injury, allowing the athlete to reach a higher percentage of his potential. Lastly, the immense variety of plyometric exercises that exist allows for a great degree of specificity for individual athletes.

The research on plyometric training is extensive, widely supporting its inclusion in youth training programs. Recent research by Michailidis (2013) aimed to determine whether preadolescent soccer players could benefit from plyometric training. Forty-five children, 10 years of age, were randomized into a control (regular sport practice) and a plyometric training group (soccer practice plus plyometric training twice a week including: hops, box jumps, skipping and ladder drills) during a 12-week period. Sprint, leg muscle power, leg strength, anaerobic power and soccer kicking performance were evaluated at baseline, mid-training and post-training. The plyometric training group greatly improved speed, vertical jump, leg strength, agility, and kicking distance after the training period (no improvement in anaerobic power seen).

A similar study by Lloyd (2012) aimed to investigate the effects of a 4-week plyometric training period on Reactive Strength Index (or RSI; a test that measures the ratio between jump height and floor contact time to assess rate of force production) during maximal hopping and leg stiffness during submaximal hopping in male youths. One hundred and twenty-nine children of ages 9, 12, and 15 years old were separated into a control (normal physical education lessons) and experimental group (twice-weekly plyometric training). Both 12 and 15 years old experimental groups’ experienced significant improvements in leg stiffness, with the 12 years-old group also making improvements in RSI.

These research studies provide support for the inclusion of plyometric training in conjunction with normal sport practice in youth athletes in order to improve athletic development. Moreover, despite improvements in RSI and leg stiffness after a short plyometric intervention, it seems to be age dependent. If performance adaptations are seen in the SSC in such a short intervention, then it is reasonable to assume that the integration of plyometric programs during different times of the season may be both effective and beneficial. The possible reasons behind the differences between 9 , 12, and 15 years old group’s adaptations is the maturity of the musculoskeletal system; younger players may benefit from basic plyometric movement training, while older pre-adolescents may see greater benefit from training more advanced plyometric competencies to help with the development of power and the application to sport.

References:

Lloyd RS, Oliver JL, Hughes MG, Williams CA. (2012). The effects of 4-weeks of plyometric training on reactive strength index and leg stiffness in male youths. J Strength Cond Res. 26(10), 2812-9.

Michailidis Y, Fatouros IG, Primpa E, Michailidis C, Avloniti A, Chatzinikolaou A, Barbero-Álvarez JC, Tsoukas D, Douroudos II, Draganidis D, Leontsini D,Margonis K, Berberidou F, Kambas A. (2013). Plyometrics’ trainability in preadolescent soccer athletes. J Strength Cond Res. 27(1), 38-49.

Young M. (2007). Maximal velocity sprint mechanics [DVD]. United States: Coaches Choice.