What is plyometric training
Plyometric training is popular among athletes in dynamic sports such as soccer. Jumping, hopping, skipping and bounding are executed with the aim of increasing dynamic muscular performance. In these exercises muscles undergo rapid elongation followed by an immediate shortening called the stretch shortening cycle. This utilises the elastic energy stored during the stretching phase (Vaczi et al, 2013).
Why is it used in soccer?
Miller et al (2006) highlights that there is a consensus plyometric training is seen to improve sport specific skills such as agility, vertical jump performance and common measures of muscle power. In soccer there is rapid movements like acceleration, deceleration, jumps and changes of direction. A high level of dynamic muscular performance is required at all levels of this training status. According to Chamari et al (2008) plyometric training is effective at improving speed using jumping exercises. Speed cannot be performed without a high rate of power production, the rapid application of force and acceleration. This is why plyometrics is so specific to soccer as it corresponds dynamically with many athletic activities such as jumping, sprinting and kicking and thus can be assigned a high priority in training by the coach.
Stretch shortening cycle
Turner & Jeffreys (2010) describe the stretch shortening cycle as an eccentric phase or stretch followed by an isometric transitional period referred to as the amortization phase, leading into an explosive concentric action. SSC is synonymous with plyometrics and is often referred to as the reversible action of muscles. Examples of SSC actions include running, walking and the winding up movement in throwing.
Kopper et al (2014) suggest that muscles can develop greater force and perform greater work in the concentric phase if prior to the shortening, stretch occur compared to shortening without prior stretch. The greater work can be put down to the muscles elastic energy during lengthening. Counter movement jumps can hightlight the magnitude of lengthening and pre load on muscle performance during the concentric contraction phase. With this jump the centre of mass is accelerating and muscle activation is minimal, while in the second phase of joint flexion the muscle activation increases to stop the vertical momentum. Bobbert & Cassius (2005) point out that aside from the enhanced propulsive force, efficient usage of the SSC also affords the athlete with a reduction in metabolic cost of movement. Economical sprinting can recover approximately 60% of the total mechanical energy. Plyometrics can enhance the athletes use of SSC by understanding the mechanics that are involved. Several mechanisms can be involved such as elastin strain energy, involuntary nervous processes, increased active range of movement and coordination.
A mechanism important in the SSC is elastic energy or sometimes referred to as potential energy and is primarily stored in the tendons. The magnitude of the stored energy theorised to be proportional to the applied force and induced deformation. Elasticity plays an important role in enhancing motor output in sports movements (Hobara et al, 2008).
Lichtwark & Wilson (2005) suggest that tendons are considered the key site for energy storage because of their ability to extend and store energy and recoil and release energy. Elastic energy stored in the tendons is the key mechanism underpinning the phenomenon of SSC. It is suggested that the tendon recoil is responsible for both increasing power output and conserving energy during locomotion. As a consequence of the tendons ability to store and release energy a goal of all athlete training should be the optimal transfer of potential energy arising from a pre-stretch being delivered to these structures. The transfer however can only be optimised through the development of muscle stiffness throughout the pre-stretch. Stiffness and compliance are therefore key terminology when explaining the efficiency of SSC and the athletes enhanced power output.
Marques et al (2013) conducted a study involving a six week plyometric training program on strength speed abilities and kicking velocity in youth soccer players. The main finding was that the group using plyometric training enhanced there running and jumping performances significantly over a short period of time while the control group never made any gains. The experimental groups vertical jump results increased by 7.7% whilst the other group had a -1.1% decrease in performance. The muscle power increases showed that adaptations in strength are occurring and are likely to be neural at this stage of development. Another study conducted by Brito et al (2014) showed low volume plyometric training for the lower body was eliciting positive increments in maximal strength and these results were deemed to be surprising. The study related the results to improvements in the neuromuscular function i.e increased neural drive to the agonist muscles, that are likely to occur through plyometric training. It should be noted in these results that in soccer gains in muscular strength should not compromise speed of movement. In fact the ultimate goal of strength training is to increase strength so that acceleration and speed in soccer specific skills such as turning, sprinting and changing direction may be enhanced (Chelly et al, 2009).
Here are some videos showing some of the plyometric drills i used to get specificity for plyometric training within soccer:
This drill mimics stopping in soccer – https://www.youtube.com/watch?v=afxa6DXCLrE
This drill mimics jumping for a header – https://www.youtube.com/watch?v=8X5aLpiTW5Q
This drill mimics a throw in – https://www.youtube.com/watch?v=MR_pntzcYZU
This drill mimics landing and changing direction before sprinting – https://www.youtube.com/watch?v=J8MZUk5NaVc
This drill is just conditioning the core for strength when changing direction – https://www.youtube.com/watch?v=73tOEeGudT0
Here are some useful links to other Plyometric blogs
Brito, J., Vasconcellos, F., Oliveira, J., Krustrup, P. & Rebelo, A. (2014) ‘Short-Term Performance Effects of Three Different Low-Volume Strength-Training Programmes in College Male Soccer Players’ Journal of Human Kinetics. 40 (0) pp. 121-128.
Bobbert. MF & Casius, U. (2005) ‘Is the countermovement on jump height due to active state development?’ Med. Sci. Sports Exer. 37 (0) pp. 440-446.
Buller, M. (2013) ‘What exactly is Plyometric training? A beginner’s guide’ Available: http://www.judgement-day.co.uk/training-guides/2013/10/what-exactly-is-plyometric-training-a-beginners-guide/#.U2hxHVf0P1U. [Last accessed 5th may].
Chamari, K., Chaouachi, A., Hambli, M., Kaouech, F., Wisloff, U. & Castagna, C . (2008) ‘The five-jump test for distance as a field test to assess lower-limb explosive power in soccer players’ Strength & Conditioning Journal. 22 (0) pp. 944-950.
Chelly, M.S., Fathloun, M., Cherif, N., Amar, M.B., Tabka, Z. & Praagh, E.V. (2009) ‘Effects of a back squat training program on leg power, jump, and sprint performances in junior soccer players’ Strength & Conditioning Journal. 23 (8) pp. 2241-2249.
De-Ben, L. (2013) ‘Plyometric training’ Available: http://fitnessblogger.net/plyometrics-training/. [Last accessed 5th may].
Hobara, H., Kimura, K., Omuro, K., Gomi, K., Muraoka, T., lso, S. & Kanosue, K. (2008) ‘Determinants of difference in leg stiffness between endurance- and power-trained athletes’ Journal of biomechanics. 41 (0) pp. 506-514.
Kopper, B., Csende, Z., Trzaskoma, L. & Tihanyi, J. (2014). Stretch-shortening cycle characteristics during vertical jumps carried out with small and large range of motion. Journal of Electromyography & Kinesiology. 24 (2), 233-239.
Lichtwark, G.A & Wilson, A.M. (2005) ‘In vivo mechanical properties of the human Achilles tendon during one-legged hoping’ J Exp Biol. 208 (0) pp. 4715-4725.
Marques, M.C., Pereira, A., Reis, I.G. & Van Den Tillar, R. (2013) ‘Does an in-Season 6-Week Combined Sprint and Jump Training Program Improve Strength-Speed Abilities and Kicking Performance in Young Soccer Players?’ Journal of Human Kinetics. 39 (0) pp. 157-166.
Miller, M.G., Herniman, J.J., Richard, M.D., Cheatham, C.C. & Michael, T.J. (2006) ‘The effects of a 6 week plyometric training program on agility’ Journal of Sports Science & Medicine. 5 (0) pp. 459-465.
Nasm. (2013) ‘Developing Power in Everyday Athletes with Plyometrics’ Available: http://blog.nasm.org/fitness/developing-power-in-everyday-athletes-with-plyometrics/. [Last accessed 5th may].
Turner, A., Jeffreys, I. (2010) ‘The Stretch-Shortening Cycle: Proposed Mechanisms and Methods for Enhancement’ Strength & Conditioning Journal. 32 (4) pp. 87-99.
Vazci, M., Tollar, J., Meszler, B., Juhasz, I. & Karsai, I. (2013) ‘Short-Term High Intensity Plyometric Training Program Improves Strength, Power and Agility in Male Soccer Players’ Journal of Human Kinetics. 36 (0) pp. 17-26.