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Impact of plyometrics on muscle hypertrophy

by P. Debraux | 13 September 2022

fitness, hypertrophy, muscle, plyometrics, training, sport, maximal, power, science

Naturally present in many sports activities and in certain training programs, plyometric exercises (jump exercises, for example) have the particularity of making optimal use of the "stretch-shortening" cycle. This consists of a rapid eccentric action immediately followed by a rapid concentric action of the same muscle-tendon unit. The main advantage of this type of contraction compared to isolated concentric, eccentric or isometric contractions is the use of the elastic potential energy stored during the eccentric phase of the movement. The kinetic energy used in this way in the movement allows to produce great mechanical power.

Plyometric training based on jumps allows for the improvement of numerous qualities related to physical performance such as strength, power, speed and balance, but also certain parameters related to health such as bone mineral density, injury prevention and the prevention of falls. These benefits are attributable to the increase in neuromuscular activation (recruitment of motor units, firing frequency, synchronization) and to better inter-muscular coordination (decrease in antagonist co-activation). Regarding muscle hypertrophy, the existing literature provides inconsistent results due to the protocols or the heterogeneity of the target audience. In addition, factors such as age, sex, training level and certain training variables such as the frequency of sessions, the number of jumps per session and the duration of training seem to moderate the effects of plyometrics on the measurements of physical qualities. So what about muscle hypertrophy and plyometric training?

The Study

To answer this question, an international team of researchers conducted a meta-analysis to evaluate the impact of plyometric training based on vertical jumps on muscle hypertrophy of the quadriceps and plantar flexors. For this, the authors analyzed 15 randomized controlled studies, including 478 participants. Only 2 studies recruited only women, 1 study recruited both women and men and 12 studies recruited only men. Regarding training level, 10 studies recruited healthy but untrained individuals and 5 studies included athletes.

Regarding hypertrophy, 4 studies examined knee extensor hypertrophy, 4 studies examined plantar flexor hypertrophy. The remaining 7 studies examined thigh or calf volume. To measure hypertrophy, 7 studies used ultrasound imaging, 6 studies used predictive equations, 1 study used muscle biopsy, and 1 study used a tape measure.

Most studies used different types of jumps in their program (eg, bilateral/unilateral vertical jumps and horizontal jumps). The training protocols lasted between 4 and 26 weeks with a weekly session frequency of 2 to 7. The duration of each session ranged from 5 to 60 minutes. And the total volume of weekly jumps ranged from 60 to 520 jumps.

Results & Analyzes

The main results of this meta-analysis show that plyometric training based on vertical jumps causes trivial to moderate effects on muscle hypertrophy, regardless of age, sex or training experience. Subanalyses show that the effect is greater in non-athletes, the effects are moderate for knee extensors and equivocal for plantar flexors. Meta-regression analyses showed that the effects on muscle hypertrophy were moderated by weekly session frequency, with more sessions resulting in greater hypertrophy. But no relationship was found with the total number of weekly jumps.

The fact that athletes obtain lower benefits than non-athletes is to be expected, as their margin of progression on such exercises is probably reduced due to the years of training already completed. In non-athletes, 11.5-18.8% increase in quadriceps cross-sectional area was observed, whereas for athletes, the increase in cross-sectional area of the whole thigh was only 9.9%.

Regarding training frequency, most protocols used 2 or 3 sessions per week. Three sessions resulted in a 12.8-25.8% increase in vastus lateralis cross-sectional area, while 2 sessions resulted in a 14% increase in thigh volume. The main benefit of playing with the frequency of weekly sessions is its effect on the distribution of training volume (see our article on this topic). A larger volume leads to better results on muscle hypertrophy.

Practical Applications

Based on the results of this meta-analysis, it would appear that plyometric jump training could not only improve neuromotor control of active muscles but could also increase muscle hypertrophy, in proportions that would depend on the training experience.

Several authors have mentioned the limitations of plyometric training for hypertrophy purposes due to the very short time under tension experienced by the active muscles during jumps, thus reducing the mechanical stimulus. In addition, progressive overloading is limited in this type of exercise since the training stimulus is based on the speed of contraction and additional load could slow down the movement, thus corrupting the adaptations initially sought.

It is important to note that plyometric training tends to preferentially hypertrophy type II (so-called "fast") muscle fibers, and this is probably due to the fact that the movement involves the recruitment of motor units with a high activation threshold. However, a plyometric session also induces particularly marked muscle damage to type II fibers. Muscle damage is often mentioned as a potential mechanism for muscle hypertrophy, but evidence of direct causality is almost non-existent. One possible explanation involves the number of repetitions in a set, and the repetition of sets, the increasing fatigue and the slowing of muscle contraction induced by this fatigue which would allow for a greater total time under tension to accumulate and thus stimulate protein synthesis.

In conclusion, plyometrics has the potential to improve muscle hypertrophy but to a lesser extent than traditional resistance training. It remains an excellent way to improve the ability to recruit high-threshold motor units, and coupling plyometrics with traditional strength training will likely result in some additional muscle hypertrophy.

References

  1. Arntz F, Mkaouer B, Markov A, Schoenfeld BJ, Moran J, Ramirez-Campillo R, Bherens M, Baumert P, Erskine RM, Hauser L and Chaabene H. Effect of plyometric jump training on skeletal muscle hypertrophy in healthy individuals: A systematic review with multilevel meta-analysis. Front Physiol 13 : 888464, 2022.

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