There are various gradations of plyometric exercise, and it is considered prudent to start with low-stress ones before progressing to more difficult ones. One of the most stressful plyometric exercises is depth-jumping, in which one jumps down from a box and, after contacting the ground, immediately jumps vertically. This is considered dangerous for anyone who does not already have a strong lower body and has not progressed from low-stress, through moderate-stress, to high-stress plyometric exercise. Various sources have recommended being able to squat with 1.5 times one’s bodyweight before taking on a serious plyometric exercise program. However, it is generally considered safe for people in good health without orthopedic problems to perform low-stress plyometric exercises like low bounces, hops, and jumps.
A recent study by Chelly et al. in the Journal of Strength and Conditioning Research (Vol 24, no. 10, pp. 2670-2676, 2010), showed how effective plyometric training can be.
A group of experienced young male soccer players, average age 19 years, trained as follows:
- August - preseason training consisting of light resistance exercise and calisthenics
- September through March (the competitive season) - The players trained 5 days per week for 90 minutes by doing skill and tactical drills along with 30 minutes of continuous play. On one day per week they engaged in a competitive soccer game against another team.
Group 1 only did the training program above.
Group 2 did the training program above plus from January-March they also did the following plyometric training twice per week:
- Week 1: 5 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
- Week 2: 7 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
- Week 3: 10 sets of jumping over ten 40-cm (24“) hurdles spaced 1 meter (39.4”) apart
- Week 4: 5 sets of jumping over ten 60-cm (36“) hurdles spaced 1 meter (39.4”) apart
- Week 5: 4 sets of depth-jumps from a 40-cm (24“) box
- Week 6: 4 sets of depth-jumps from a 40-cm (24“) box
- Week 7: 4 sets of depth-jumps from a 40-cm (24“) box
- Week 8: 4 sets of depth-jumps from a 40-cm (24“) box
Extensive testing on speed, power, and jump height was performed before and after the training.
The group that did regular soccer training did not show significant improvement in any of the pre-post tests.
The group that did plyometric training in addition to their regular soccer training showed the following statistically significant improvements:
- Thigh muscle volume: +2.5%
- Cycle ergometer absolute power: +4.5%
- Cycle ergometer power relative to body mass: +5.9%
- Jump height without a countermovement: +8.3%
- Jump height with a countermovement: +2.5%
- 40-meter sprint first step velocity: +18.2%
- 40-meter sprint velocity over first 5 meters: +10.0%
- 40-meter sprint velocity between 35 and 40 meters: +9.8%
Although not all studies of plyometric training have produced improvements of this magnitude, it appears that the evidence supports inclusion of plyometric exercise in physical training programs for sports involving sprinting and/or jumping.
NOTE: This description of experimental results is for informational purposes only and does not constitute a recommendation. Anyone engaging in an exercise program should obtain proper medical authorization before doing so.