I have been implementing a number of plyometric exercises eg. medicine-ball throws/jumping, into your strength and conditioning to work alongside your skills sessions, and some of you are interested in finding out a little more about it?
Firstly let’s say that there is a multitude of information out there; I am going to compile an online resource for your perusal.
Plyometrics is characterised by a rapid lengthening of a muscle under tension (eccentric contraction) followed immediately by a forceful shortening (concentric contraction) of that muscle (Decker & McCaw, 2012); this process of lengthening and shortening being the stretch-shortening cycle (SSC).
Training this SSC will, amongst others, facilitate a greater power output across the concentric phase of movement (Aboodarda, et al., 2014; Decker & McCaw, 2012; Komi, 1984; Komi, 1992; Moore & Schilling, 2005), tested regularly through jumping; an important performance component of many sports. A number of training modalities have been used to enhance jumping performance, through the stretch-shortening cycle, including plyometrics (Crowther, Spinks, Leicht, and Spinks, 2007).
A number of different mechanisms are theorised to describe the stretch-shortening cycle.
Turner and Jeffrey’s (2010) looked at currently accepted theories behind the mechanisms of the SSC. They investigated the bodies soft tissue elastic strain energy, involuntary nervous processes, increased active range of movement, length-tension characteristics of muscle and tendon, and enhanced co-ordination.
The proposed mechanism surrounding the elastic energy, suggests that an eccentric contraction immediately preceding a concentric contraction will significantly increase the force generated by the resultant concentric contraction due the storage of elastic energy. This increase of force generation most effective when the preceding eccentric contraction is within a short range and is performed quickly (Chmielewski, Myer, Kauffman, and Tillman, 2006; Wilk, et al., 1993).
A neuromuscular proprioception (bodies’ spatial awareness) mechanism has also been proposed involving the muscle spindles and golgi tendon organs (GTO). Firstly, stretching a muscle and approaching a length that could potentially damage the muscle–tendon complex, activates the spindle creating a stretch reflex, where the muscle reflexively stimulates an opposite contraction of the same muscle, therefore stopping potential injury; allowing the muscle to return to its original length (Flanagan & Comyns, 2008; Chmielewski, et al., 2006; Wilk, et al., 1993). The GTO works to changes in tension, rather than length. Situated in the tendon itself, the GTO is stimulated by tension in the tendon; working with the spinal cord, an inhibitory feedback is sent initiating a stimulation of the opposite muscle (Chmielewski, et al., 2006).
Based on current review, elastic energy through tendon recoil seems to be the most plausible explanation for the SSC mechanism, with effects of the muscle spindle remaining debatable because of insignificant findings (Turner & Jeffreys, 2010); similarly concluded by Wilson and Flanagan (2008).
Plyometric movement, regarding the SSC, is broken into three sections:
Loading Phase: Where the muscle-tendon units of the prime movers are stretched as a result of loading applied to a joint.
Coupling Phase: The transition between the loading and unloading phase.
Unloading Phase: Occurring immediately after the coupling phase; involves the shortening of the muscle-tendon unit. The contact time is an important determinant in whether performance will be enhanced from the stretch-shortening cycle, and prolonged contact times should be avoided. (Chmielewski, et al., 2006).
The three phases shown below in Figure 1 shows examples of the phases of a plyometric activity in (A) Lower extremity (B) Upper extremity (C) Trunk plyometric exercises.
Taken from Chmielewski, et al. (2006) these three examples of plyometric exercises, but any exercise performed where there is a ‘pre-movement’ then an ‘explosive movement after is too! Including countermovement jumps, hurdle-jumping, and box-jumping (Decker & McCaw, 2012) for the lower limb and throwing, trunk rotation and medicine ball exercises for the upper limb (Chmielewski, et al., 2006).
So why am I doing these exact exercises?
Let’s look at the exercises that I have been doing with you.
The following video shows good technique and description of a tuck jump, a medicine ball wall throw moving through trunk rotation and lateral hops over a hurdle.
The medicine ball wall throw, when performed correctly, trains the SSC of all muscles involved in translating power up through the body, to outstretched long lever arms; creating a situation for effective power output over the entire body in a rotatory movement, imitating for example a rugby ball pass.
The lateral hop over a mini hurdle, where the feet aren’t coming very far off of the floor provides a learning platform for very quick movement, with little contact time with the floor, progressing to the tuck jump, increasing lower limb power output, with little contact time, driving from the musculature of the legs. For both of these exercises working power output, we’re effectively setting a training exercise which could increase capacity for increased speed; for sprints, lateral agility and optimal acceleration.
This short contact time, and its importance shown in the video below.
Does Plyometrics work?
Plyometric programs which range from 6-15 weeks generally improve performance; however some gains appear to be greater when plyometrics is combined with weight training. This combination induces 90% increases in leg strength after only 6 weeks. In addition to increasing strength, other performance benefits attributed to plyometric exercise are faster rate of force development and DOMS (Chmielewski, et al., 2006).
Faigenbaum, et al. (2007) looked at medicine ball throws, a 9 metre print and an agility run amongst other variables of twenty-nine college-aged males after 8 weeks of training, which showed the addition of plyometric training to a resistance program may be more beneficial than resistance training and static stretching for enhancing power output.
Fatouros’ (2000) study also provided support for the combination of weightlifting exercises with plyometric drills to improve vertical jumping ability and explosive performance, after looking at forty-one men, training 3 times a week, with a variety of protocols, compared to a control group.
Stretching prior to plyometrics can result in small decreases in performance, but it can be suggested that neuromuscular inhibition may be the reason rather than changes in muscle stiffness; (Knudson et al., 2001) just remember to warm-up as effective for you. Also remember also that for maximising performance and possibly reducing injury, plyometric training should be preceded by strength training (Turner & Jeffreys, 2010).
Take Home Point:
The reasoning behind incorporating plyometric sessions into our training is that it works in optimally training the Stretch-Shortening Cycle – allowing us to rapidly and effectively produce power from our muscles: important for every aspect of sport.
Aboodarda, S. J., Byrne, J. M., Samson, M., Wilson, B. D., Mokhtar, A. H. & Behm, D.G. (2014). Does performing drop jumps with additional eccentric loading improve jump performance? Journal of Strength & Conditioning Research. 28(8), pp. 2314–2323.
Chmielewski, T. L., Myer, G. D., Kauffman, D. & Tillman, S. M. (2006). Plyometric Exercise in the Rehabilitation of Athletes: Physiological Responses and Clinical Application. Orthopaedic Sports Physical Therapy. 36(5), pp. 308-319.
Crowther, R. G., Spinks, W. L., Leicht, A. S. & Spinks, C. D. (2007). Kinematic Responses to plyometric exercises conducted on compliant and non-compliant surfaces. Journal of Strength and Conditioning Research. 21(2), pp. 460–465.
Decker, A. J. & McCaw, S. T. (2012). Target heights alter the energetics of drop jumps when drop height is held constant. Journal Strength Conditioning Research. 26(12), pp.3237–3242.
Faigenbaum, A. D., McFarland, J. E., Keiper, F. B, Tevlin, W., Ratamess, N. A., Kang, J. & Hoffman, J. R. (2007). Effects of a short-term plyometric and resistance training program on fitness performance in boys age 12 to 15 years. Journal of Sports Science and Medicine. 6, pp. 519-525.
Fatouros, I. G., Jamurtas, A. Z., Leontsini, D., Taxildaris, K., Aggelousis, N., Kostopoulos, N. & Buckenmeyer, P. (2000). Evaluation of plyometric exercise training, weight training, and their combination on vertical jumping performance and leg strength. Journal of Strength and Conditioning Research. 14(4), pp. 470–476.
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Knudson, D., Bennett, K., Corn, R., Leick, D. & Smith, C. J. (2001). Acute effects of stretching are not evident in the kinematics of the vertical jump. Strength and Conditioning Research. 15(1), pp. 98-101.
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Komi, P. V. (1992). Strength and Power in Sport. Malden, MA: Blackwell Scientific Publications.
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Potteiger, J. A., Lockwood, R. H., Haub, M. D., Dolezal, B. A., Almuzaini, K. S., Schroeder, J. M. & Zebas, C. J. (1999). Muscle power and fibre characteristics following 8 weeks of plyometric training. Journal of Strength Conditioning Research. 13, pp. 275–279.
Turner, A. N. & Jeffreys, I. (2010). The Stretch-Shortening Cycle: Proposed Mechanisms and Methods for Enhancement. Strength and conditioning Journal. 32(4), pp. 87-99.
Wilk, K. E., Voight, M., Keirns, M., Cambetta, V., Andrews, I. R. & Dillman, C. (1993). Stretch-Shortening Drills for the Upper Extremities: Theory and Clinical Application. Journal of Orthopaedic Sports and Physical Therapy. 17(5), pp. 225-239.
Wilson, J. M., & Flanagan, E. P. (2008). The role of elastic energy in activities with high force and power requirements: a brief review. Journal of Strength and Conditioning. 22, pp. 1705–1715.