Football requires the use of various multi-directional, powerful and explosive motions. These include jumping, kicking, sprints, directional changes, acceleration and deceleration (Ronnestad et al., 2008; Michailidis et al., 2013; Franco-Márquez et al., 2015). These fast and powerful movements are fundamental motions of football, and all utilise the stretch-shortening cycle (SSC) of muscles (Michailidis et al., 2013). The SSC is muscular function whereby the muscle-tendon complex is lengthened through an eccentric motion, quickly followed by muscle shortening during a concentric contraction (Taube et al., 2012). The individual’s ability to perform the SSC determines the power they can produce (Taube et al., 2012); thus training this system is crucial to improve the power and performance of footballers (Michailidis et al., 2013; Franco-Márquez et al., 2015). In order to train the SSC, plyometric exercises are used as an effective method of utilising the SSC through using an eccentric contraction, rapidly followed by a concentric contraction (Davies et al., 2015).

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Davies et al. (2015) explained the three phases of plyometrics: the eccentric pre-stretch, the amoritization phase, and the concentric shortening phase.

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The Eccentric Pre-Stretch Phase

Also known as pre-loading and potentiation phase, the eccentric pre-stretch phase works to stretch the muscle spindle of the muscle-tendon complex and non-contractile tissues within the muscle such as the elastic components. This phase is important for enhancing the force of the followed concentric contraction.

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Amoritization Phase

The amoritization phase, also known as time to rebound, is the time of elastic recoil between the eccentric pre-stretch and generating force for the concentric contraction. The main goal of plyometrics is to make this time shorter; the shorter this phase, the more powerful and explosive the plyometric movement, as more stored energy can be utilised. If this phase is delayed, this stored energy is released as heat and the stretch reflex is not activated.

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Concentric Shortening Phase

The final phase of the plyometric movement is the concentric shortening phase. If the stored energy and elastic properties of the pre-stretched muscle is utilised effectively, this would result in an explosive and powerful concentric phase.  

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Plyometric exercise has been shown to increase jump height, improve sprint speed as well as being an effective strategy for injury prevention, specifically for Anterior Cruciate Ligament (ACL) injuries (Davies et al., 2015). Ronnestad et al. (2008) found this is true with either bodyweight plyometric exercise, or when external load is applied.

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References

Davies, G., Riemann, B., and Manske, R. (2015) Current Concepts of Plyometric Exercise. International Journal of Sports Physical Therapy. Vol. 10, No. 6: 760-786

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Franco-Márquez, F., Rodríguez-Rosell, D., González-Suárez, J., Pareja-Blanco, F., Mora-Custodio, R., Yañez-García, J., and González-Badillo, J. (2015) Effects of Combined Resistance Training and Plyometrics on Physical Performance in Young Soccer Players. International Journal of Sports Medicine.

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Michailidis, Y., Fatouros, I., Primpa, E., Michailidis, C., Avloniti, A., Chatzinikolaou, A., Barbero-Álvarez, J., Tsoukas, D., Douroudos, I., Draganidis, D., Leontsini, D., Margonis, K., Berberidou, F., and Kambas, A. (2013) Plyometrics' Trainability in Preadolescent Soccer Athletes. The Journal of Strength & Conditioning Research. Vol. 27, No. 1: 38-49

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Ronnestad, B., Kvamme, N., Sunde, A., and Raastad, T. (2008) Short-Term Effects of Strength and Plyometric Training on Sprint and Jump Performance in Professional Soccer Players. The Journal of Strength & Conditioning Research. Vol. 22, No. 3: 773-780

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Taube, W., Leukel, C., and Gollhofer, A. (2012) How Neurons Make Us Jump: The Neural Control of Stretch-Shortening Cycle Movements. Exercise and Sport Sciences Reviews. Vol. 40, No. 2: 106-115