What is plyometric training?

Plyometric Training: The Science Behind Explosive Power

Plyometric training is widely recognised as an effective method for developing explosive power by training the neuromuscular system to produce high levels of force in minimal time. Within modern sport and performance settings, plyometrics are frequently used to enhance athletic qualities such as sprint speed, jump performance, and rapid changes of direction. Early work in the 1980s by Russ Polhemus and Ed Burkardt demonstrated that combining plyometric exercises with traditional resistance training led to greater improvements in performance than either method alone. Their findings showed improvements in strength and speed, alongside additional benefits related to movement efficiency and injury reduction (Radcliffe and Farentinos, 1999).

At a physiological level, plyometric training relies on two key mechanisms: force production during eccentric muscle actions and the stretch-shortening cycle (SSC). Radcliffe and Farentinos (1999) describe plyometrics as movements that utilise a rapid pre-stretch or counter-movement prior to a powerful concentric contraction. This process allows the body to exploit the elastic properties of skeletal muscle and tendons, while also enhancing neural activation. As a result, force output during plyometric movements exceeds that of isolated concentric contractions, making them particularly effective for explosive athletic tasks (Hewett et al., 1996).

From a mechanical perspective, the effectiveness of plyometric exercise is largely determined by the behaviour of the muscle–tendon unit during rapid loading. When an agonist muscle undergoes a fast eccentric contraction, the series elastic components (SEC) of the muscle and tendon lengthen and store elastic energy, behaving similarly to a spring (Komi, 1973). If this eccentric action is followed immediately by a concentric contraction, the stored elastic energy is released and contributes to the overall force produced. This additional contribution enhances power output by assisting the muscle–tendon unit in returning to its resting length. However, if there is a delay between the eccentric and concentric phases, the stored energy dissipates as heat and its contribution to force production is reduced (Asmussen and Bonde-Peterson, 1974).

Alongside these mechanical processes, neurophysiological mechanisms also play a crucial role in plyometric performance. In particular, the stretch reflex is an involuntary response that occurs when a muscle experiences a rapid stretch. Muscle spindles, which act as proprioceptive sensors within skeletal muscle, detect both the magnitude and velocity of this stretch. When activated quickly, muscle spindle activity increases alpha motor neuron excitation, leading to greater motor unit recruitment and enhanced force production during the concentric phase (Baechle and Earle, 2008). Similar to the mechanical contribution of the SEC, the effectiveness of the stretch reflex is highly time-dependent, and prolonged transition phases reduce its potentiating effect.

The interaction of these mechanical and neurophysiological mechanisms occurs through the stretch-shortening cycle (SSC). The SSC is commonly described as consisting of three phases: the eccentric phase, the amortization (or transition) phase, and the concentric phase. During the eccentric phase, muscles are preloaded, elastic energy is stored within the SEC, and muscle spindle activation is initiated. The amortization phase represents the brief transition between eccentric loading and concentric contraction and is a critical determinant of plyometric effectiveness. Shorter transition times allow greater use of stored elastic energy and neural potentiation, whereas longer transition phases result in energy dissipation and reduced force output (Baechle and Earle, 2008). During the concentric phase, stored elastic energy and neural drive combine to produce force levels greater than those achievable through concentric action alone.

Understanding the mechanisms underpinning plyometric training highlights why technique, timing, and appropriate progression are essential. When implemented correctly, plyometric exercises can significantly enhance athletic performance while improving movement efficiency and resilience. However, poorly coached or inappropriately progressed plyometric training may reduce effectiveness and increase injury risk. For this reason, plyometrics should not be viewed as simple jump training, but as a highly specific training method that requires informed coaching, individualisation, and a clear understanding of the underlying science.

Key Takeaways for Athletes & Coaches

• Plyometric training enhances explosive power by exploiting the stretch-shortening cycle.

• Effective plyometrics rely on both mechanical (elastic energy) and neural (stretch reflex) mechanisms.

• Short transition times between eccentric and concentric phases are critical for maximising force output.

• Proper technique, progression, and coaching are essential to maximise benefits and minimise injury risk.

Reference

Asmussen, E. and Bonde-Peterson, F. (1974) 'Storage of elastic energy in skeletal muscles in men', Acta physiol Scand, 91, pp. 385-392

Baechle, T. and Earle, R. (2008) Essentials of strength and conditioning/ National strength and conditioning association. United States: Human Kinetics. 3rd ed. Hewett, T. et al. (1996) 'Plyometrics training in female athletes', Am J Sports Med, 24, pp. 765-773.

Jones, D. and Rutherford, O. (1987) Human muscle strength training: the effects of three different regimes and the nature of the resultant changes. The department of medicine, university college London. Vol 391, pp. 1-11.

Komi, P. (1973) Measurement of the force- velocity relationship in human muscle under concentric and eccentric contractions. Medicine and Sport: Biomechanics. Vol 8, pp. 224-229.