How To Utilise Plyometric Training To Convert Strength Into Power
Plyometric exercises are an effective form of training to develop muscle power for sports such as sprinting and jumping in which speed and explosiveness are essential (Radcliffe & Farentinos, 1999). Plyometrics can be used to condition the muscles through the effective use of the stretch shortening cycle (SSC) to produce maximum force in the shortest possible time (Wilson & Flanagan, 2008). Examples of plyometric exercises are depth jumps and hopping and bounding activities (Matthew, 2003).
There are a number of mechanisms proposed to enhance the actions of the SSC resulting in more muscle force and power output. These involve both mechanical and neurological actions (Neptune, McGowan, & Fiandt, 2009). High eccentric forces, storage and release of elastic energy as well as stretch-reflex activation to increase muscle recruitment have been attributed to the actions of the SSC (Flanagan & Comyns, 2008).
One proposed mechanism for the enhancement during the concentric phase of the SSC has been attributed to the storage and reutilization of elastic energy (Turner & Jeffreys, 2010). During the eccentric phase, the active muscles are pre-stretched and absorb and temporarily store energy. This is then reused during the concentric contraction phase of the SSC (Turner & Jeffreys, 2010).
Two proprioceptors are of most significance in the SSC and cause an increased excitability for an optimal reaction by the neuromuscular system (Flanagan & Comyns, 2008). The first is the muscle spindle, which reacts to the rapid changes in length to protect the muscle–tendon complex. As eccentric stretching approaches a rate that could potentially damage the muscle–tendon complex, the spindle activates and reflexively stimulates an opposite contraction of the agonist (Flanagan & Comyns, 2008), resulting in a reflex contraction of the stretched muscle that enables the muscle to return to its present length. The second is the Golgi tendon organ (GTO), which responds to changes in tension rather than those in length and inhibits agonist muscles and facilitates antagonist muscles. These inhibitory effects function as a protective mechanism (Turner & Jeffreys, 2010). When muscle contractile forces reach a point at which damage to the muscle–tendon complex may occur, GTOs increase afferent activity, resulting in inhibition of the motor neurons innervating the stretched muscles while simultaneously exciting the motor neurons of the antagonist muscles (Turner & Jeffreys, 2010). This may reduce the muscle reflex contraction that follows the eccentric stretch phase. It is believed that during plyometric exercise, the excitatory threshold of the GTOs is increased, hence they become less likely to send signals to limit force production. One of the primary training goals for enhancing the SSC is to maximise the positive effects of the muscle spindle while minimizing the negative effects of the GTO.
It is also thought that greater recruitment of motor units during the eccentric phase may enhance the concentric contraction of the SSC as a result of neural potentiation of the muscle contractile machinery during eccentric loading (Flanagan & Comyns, 2008). Performance enhancements from the isometric contraction or the preceding stretch may result from a greater level of neural excitation before the concentric movement (Flanagan & Comyns, 2008).
Phases of the SSC
Figure 1. The SSC is usually expressed in three different phases. Adapted from (Neptune et al., 2009).
During the eccentric phase (a) preloading and stretching of the muscles occur as soon as the muscles start to experience an eccentric contraction. Muscles that are actively stretched develop high forces, store elastic energy, and elicit a stretch-reflex activation response (Komi, 1992). The rapid eccentric contraction serves to stretch the elastic component of the muscle and stimulates the muscle spindle and activates the stretch reflex, eventually causing the muscle to contract (Komi, 1992). A high level of eccentric strength is needed, as inadequate strength will result in a slow rate of stretch and less activation of the stretch reflex. The amortisation phase (b) refers to the time between eccentric and concentric phases. This phase is a very important part of a plyometric exercise and must remain short (Neptune et al., 2009). It represents the time it takes from landing to take off and is crucial for power development. The longer the amortisation phase the greater the loss of stored elastic energy. The concentric phase (c) is when the muscles shorten with high force and stored elastic energy is used with the voluntary, concentric muscle contraction to contribute to the increases in muscle work and power output (Neptune et al., 2009).
Getting Ready for Plyometrics
As intensity is vital to successful plyometrics training, this form of training places considerable stress on the joints, bones and connective tissue (Chu, 1998). In order to perform effective and safe training sessions there are several variables to consider. It is important that a sequence of progression is introduced that will allow the athlete to move from basic to advance exercises in a safe and structured manner (Turner & Jeffreys, 2010). Jumping and landing are two basic plyometric skills that must be learned in order to optimise performance and reduce the risk of injury (Turner & Jeffreys, 2010). It is important that the athlete can land effectively before jumping and the landing surface should be able to absorb some of the shock.
Turner & Jeffreys (2010) recommend the use of the plyometric pyramid as a method of introducing plyometric exercises for athletes. This involves 3 stages of exercises:
- Stage 1. The box jump stage where the athlete develops basic jumping and landing abilities in a controlled environment.
- Stage 2. The jump and stick stage where the athlete continues to build on their landing capacity and their ability to control eccentric forces. Progression can be used in this stage to increase the amplitude of movements.
- Stage 3. The short response jumps stage where the athlete begins proper plyometric training and the SSC is used to enhance subsequent concentric performance. In this stage it is important to maintain effective landing mechanics and body control with the aim to minimise ground contact time while the athlete performs jump activities.
Designing a Plyometrics Program
Intensity is a measure of the effort involved in performing a given task and is an important variable in determining the overall stress of a training session (Chu, 1998). All repetitions in a plyometric exercise are performed at maximum speed and power to maximise the SSC response and plyometric effect of the movement (Matthew, 2003). This can be achieved by emphasising the importance of minimising ground contact times when coaching. New plyometrics drills can be performed at below maximum intensity until technique is fully grasped.
Contacts per session
Contacts in plyometrics signify the number of single foot or hand contacts with the ground during a plyometric session. Table 1 indicates an example of contacts per session of plyometrics for beginner, intermediate and advanced athletes, with respect to intensity.
Table 1. Contacts per session
Rest Between Sets
Rest and recovery are crucial variables in a plyometric program (Chu, 1998). Rest is the time taken between each exercise or set while recovery is the amount of time needed before the workout can be repeated. Rest duration depends on work duration and the type of drill or exercise used (Radcliffe & Farentinos, 1999). Table 2 indicates sample rest interval times between repetitions, sets and exercises that depend on exercise duration.
Table 2. Work and Rest Periods
Plyometrics can be performed two to three times per week. If the athlete alternates upper and lower body plyometric drills then additional sessions may be added. For beginners two sessions per week should be adequate. An example program for a beginner athlete is shown in Table 3, where lower body plyometric exercises are indicated each with their corresponding number of sets and repetitions, resting periods and total number of contacts.
Table 3. Sample beginner program
Plyometrics exercise has become an excellent training tool for the training regimens of all levels of coaches and athletes and has evolved into a widely accepted and greatly effective tool to improve speed and power. It is important for strength and conditioning coaches to learn how to utilise plyometrics in order to enhance their athletes speed and power.
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Chu, D. A. (1998). Jumping Into Plyometrics (pp.28-35). USA, Human Kinetics.
Flanagan, E. P., & Comyns, T. M. (2008). The use of contact time and the reactive strength index to optimize fast stretch-shortening cycle training. Strength & Conditioning Journal, 30, 32–38.
Komi, P. V. (2003). Stretch-shortening cycle. Strength and power in sport, 3, 169–179.
Matthew, K. (2003). Theoretical and practical applications for plyometrics training. NSCA Perform Train, J 2(10–13).
Neptune, R. R., McGowan, C. P., & Fiandt, J. M. (2009). The influence of muscle physiology and advanced technology on sports performance. Annual review of biomedical engineering, 11, 81–107.
Radcliffe, J. C., & Farentinos, R. C. (1999). High-Powered Plyometrics. (pp.31-36). USA, Human Kinetics.
Turner, A. N., & Jeffreys, I. (2010). The stretch-shortening cycle: proposed mechanisms and methods for enhancement. Strength & Conditioning Journal, 32, 87–99.
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 Research / National Strength & Conditioning Association, 22, 1705–1715.