Effects of Caffeine Supplementation on Exercise Performance in Volleyball Players: A Systematic Review and Meta-Analysis.

The ergogenic effects of caffeine in team sports, particularly volleyball, have received significant research attention. This study sought to examine the effects of caffeine on both volleyball-specific and general performance outcomes. This systematic review comprises 11 studies, each utilizing a blinded crossover experimental design. A meta-analysis was conducted using a random-effect model to determine the standardized mean difference (SMD), estimated by Hedges' g, with a 95% confidence interval (CI). Caffeine supplementation improved volleyball-specific outcomes, including attack and serve accuracy (SMD: 0.50; 95% CI: 0.11-0.90; = 0.01). Regarding nonspecific outcomes, caffeine increased single-jump performance (SMD: 0.23; 95% CI: 0.02-0.44; = 0.03), repeated-jump performance (SMD: 0.51; 95% CI: 0.05-0.96; = 0.03), and handgrip strength (SMD: 0.23; 95% CI: 0.03-0.42; = 0.02), while decreasing agility test completion time (SMD: -0.32; 95% CI: -0.60-0.03; = 0.03). Furthermore, caffeine increased the frequency of positive game actions during simulated volleyball matches (SMD: 0.84; 95% CI: 0.26-1.43; < 0.01). Caffeine supplementation enhances physical performance and volleyball-specific actions during competition, supporting its role as an effective ergogenic aid for volleyball players.