The effect of low dose caffeine powder supplementation on serve speed, spike speed, and speed-endurance in elite sitting volleyball players: a randomized double-blind crossover study.

Although this improvement did not reach statistical significance after correction for multiple comparisons.

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However, the medium effect size and directionally favorable confidence interval (95% CI: 0.21 to 3.02 km/h) suggest a trend toward significance, which warrants cautious interpretation and further investigation.

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While a 3 mg/kg dose of caffeine showed a trend toward improving serve speed, the effect did not remain statistically significant after correction for multiple comparisons, and no meaningful improvements were observed in spike or speed-endurance performance.

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