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Effects of Plyometric Jump Training on Vertical Jump Height of Volleyball Players: A Systematic Review with Meta-Analysis of Randomized-Controlled Trial.

This meta-analysis aimed to assess the effects of plyometric jump training (PJT) on volleyball players' vertical jump height (VJH), comparing changes with those observed in a matched control group. A literature search in the databases of PubMed, MEDLINE, Web of Science, and SCOPUS was conducted. Only randomized-controlled trials and studies that included a pre-to-post intervention assessment of VJH were included. They involved only healthy volleyball players with no restrictions on age or sex. Data were independently extracted from the included studies by two authors. The Physiotherapy Evidence Database scale was used to assess the risk of bias, and methodological quality, of eligible studies included in the review. From 7,081 records, 14 studies were meta-analysed. A moderate Cohen's d effect size (ES = 0.82, p <0.001) was observed for VJH, with moderate heterogeneity (I 2 = 34.4%, p = 0.09) and no publication bias (Egger's test, p = 0.59). Analyses of moderator variables revealed no significant differences for PJT program duration (≤8 vs. >8 weeks, ES = 0.79 vs. 0.87, respectively), frequency (≤2 vs. >2 sessions/week, ES = 0.83 vs. 0.78, respectively), total number of sessions (≤16 vs. >16 sessions, ES = 0.73 vs. 0.92, respectively), sex (female vs. male, ES = 1.3 vs. 0.5, respectively), age (≥19 vs. <19 years of age, ES = 0.89 vs. 0.70, respectively), and volume (>2,000 vs. <2,000 jumps, ES = 0.76 vs. 0.79, respectively). In conclusion, PJT appears to be effective in inducing improvements in volleyball players' VJH. Improvements in VJH may be achieved by both male and female volleyball players, in different age groups, with programs of relatively low volume and frequency. Though PJT seems to be safe for volleyball players, it is recommended that an individualized approach, according to player position, is adopted with some players (e.g. libero) less prepared to sustain PJT loads.