Plyometric training requires appropriate technical ability as well as optimum levels of muscle strength and joint coordination. For this reason, subjects with low fitness levels or less experienced individuals are expected to benefit less from such training (3,49). However, the results of the present meta-analysis indicate equal ESs for subjects of various fitness levels (Table 2). These results might indicate that when subjects can adequately follow plyometric exercises, the training gains are independent of fitness level.
Furthermore, our results suggest that higher enhancements after plyometric training can be observed in athletes competing at the international level compared with those gains reached in athletes at the regional level (Table 2). This is further supported by a moderate correlation coefficient between years of experience and ES (Table 2) and suggests that plyometric training is essential for top-level and experienced athletes. Plyometrics improve SSC use with reduced energy consumption and higher power output, and they require high levels of coordination. These features are essential aspects of top-level athletes and optimal performance.
An interesting finding in this study is that men demonstrated higher gains compared with women (Table 2). The reasons for this difference are not clear. It could be suggested that men demonstrate higher power output and better coordination than women. However, the large difference in sample sizes between men and women and the small number of ESs available may account for this observation.
The results show similar ESs for various sport activities. Each sport has its own characteristics, and therefore specific plyometric training exercises have been applied. This confirms previous suggestions (81) that plyometric training should be performed in conditions very similar to competition to achieve sport-specific gains.
In the present study, VJH improvements are not higher when plyometrics are combined with other types of exercise (Table 3). This emphasizes the unique characteristics of plyometric training in terms of improving VJH. However, it should be mentioned that when plyometrics were combined with electrostimulation, higher ESs were observed.
The specific effects of plyometrics on VJH in the different types of vertical jumps could be of particular importance. It has been suggested that plyometric training is more effective in improving vertical jump performance in SSC jumps because it enhances the ability of subjects to use the elastic and neural benefits of the SSC (95). This also could be attributed to differences in the use of SSC characteristics (17,54). An SJ mainly consists of a concentric (push-off) phase, whereas a CMJ involves an eccentric and concentric phase (15). The results of our study support these suggestions. Specifically, our data indicate that plyometrics produce somewhat greater (although not significantly) positive effects in the fast SSC jumps (i.e., DJ) than in the concentric-only jumps (i.e., SJ) or even the slow SSC jumps (i.e., CMJ). Keeping the specificity of contraction-type training in mind (i.e., SSC muscle function), greater positive effects of plyometric training on DJs and CMJs than on SJs can be expected. However, to explain the difference in the effects of plyometric training between DJs and CMJs, we should take into account the biomechanical differences between the slow and fast SSC jumping exercises (12). Several authors (12,99) have shown a substantial difference in the mechanical output and jumping performance between slow SSC vertical jumps such as CMJs and fast SSC vertical jumps such as DJs. For these authors, the jumping technique (i.e., corporal position, movement amplitude, and ground-contact time) represents one of the most important factors to be considered when designing plyometric programs. However, in many of the studies included in this review, the researchers did not consider the above-mentioned factors when describing their plyometric programs. Therefore, it remains unclear whether the jumping technique is responsible for the somewhat greater gains observed in VJH.
Some research studies have shown that plyometric training with additional weights (vests, bars on the back, etc.) demonstrated higher gains (11,35,40,41,52), whereas others (21,34,50,60,63,66,70,72,82-84) have reported the opposite. The results of the meta-analysis indicate no differences among training conditions (Table 3). This suggests that using additional weights in training does not cause significant gains in performance. It could be suggested, then, that training with additional loads might increase not only resistance but also contact time. However, the longer the contact time, the less effective the SSC (13). Therefore, training effects using additional weights are not guaranteed.
Volume and frequency are very important parameters to take into account for an optimum plyometric training program design. The results showed that training for 10 weeks is more beneficial than similar programs of shorter duration. Similarly, treatment with more than 20 sessions increases VJH, whereas performance of more than 50 jumps per session seemed to result in the most beneficial volume (Table 4). These figures are compatible with previous recommendations (30,35,89,98). However, in agreement with previous studies (78), a short-term plyometric training program with a moderate training frequency and volume of jumps (2 d·wk−1, 840 jumps) produced similar enhancements in jumping performance but greater training efficiency compared with high training frequency (4 d·wk−1, 1680 jumps). Conceptually taken on the whole, the present data indicate that increasing the number of jumps in previously moderately trained men does not seem to be the best stimulus for improving vertical jump performance during short-term training periods compared with high jump-training volumes. These results also suggest that there is a minimum training volume threshold over which further increases in volume are no longer advantageous. It is also likely that in previously physically active subjects within the context of a short-term plyometric training cycle of 7 weeks, jumping performance training can be improved only by 50% or by a high-volume jumping program (e.g., 28 sessions of plyometric training [1680 DJs] performed for 4 sessions per week during a 7-week training period).
In conclusion, the present study demonstrates that plyometric training significantly improves VJH. The estimated improvements in VJH as a result of plyometrics could be considered as practically relevant-for example, an improvement in VJH of >7% (i.e., 3.90 cm) could be of high importance for trained athletes in sports relying on jumping performance. According to our results, subjects with more experience in sport obtained the greatest enhancements in VJH. On the other hand, subjects in both good and bad physical condition benefit equally from plyometric work, although men obtain better power results than women after plyometric training. A training volume of more than 10 weeks (with more than 20 sessions), using high intensities (with more than 50 jumps per session), is the strategy that will maximize one's probability of obtaining significant improvements in performance. It is also probable that there is a minimum training volume threshold over which further increases in volume may no longer be advantageous. Another important conclusion is that it is more beneficial to combine different types of plyometrics than to use only 1 form, whereas the best combination is SJs + CMJs + DJs. However, there are no extra benefits gained from doing plyometrics with added weight.
Plyometric training can be recommended as an effective form of physical conditioning for augmenting vertical jump performance; yet, the effects of plyometric training could vary because of a large number of variables, such as training program design, subject characteristics (gender, age), training level, the specific sport activity, familiarity with plyometric training, program duration, and training volume or intensity. These conclusions are essential and should be taken into account by strength and conditioning professionals, who must consider the most appropriate plyometric training approach based on the fundamental movement patterns, technique, volume, frequency, intensity, energy system requirements, and potential injury analysis for a given sport. Furthermore, for an individual athlete, initial training status and training experience must be considered, and specific fitness limitations should be stressed. The strength and conditioning coach may take into account the dose-response trends identified in this analysis to prescribe the appropriate level of training.
The authors have no professional relationships with companies or manufacturers that might benefit from the results of this study. The results of this study do not constitute endorsement of any product by the authors or the NSCA.
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