Caffeine shows no clear edge in female volleyball players

Caffeine is the most widely used ergogenic aid in sport, and the assumption that it reliably boosts power, jumping and reaction is close to received wisdom. That wisdom, though, was built largely on studies of male athletes or mixed-sex samples, with women's data folded in as an afterthought or absent entirely. Volleyball is a sport where explosive jumping, rapid changes of direction and sustained attention all matter, making it a reasonable test case. Until now no meta-analysis had specifically asked whether caffeine does anything measurable for female volleyball players.

The authors conducted a systematic search in March 2026 across PubMed, Web of Science, the Cochrane Library and ProQuest, with the review pre-registered in PROSPERO. They included randomised controlled trials examining acute caffeine intake and performance in female volleyball players, and pooled results using a three-level meta-analysis, an approach that handles multiple outcomes drawn from the same studies. Methodological quality was assessed with the PEDro scale and risk of bias with RoB 2, while the certainty of the overall evidence was graded using GRADE. Five studies comprising 66 female athletes met inclusion criteria, testing caffeine doses ranging from 2 to 6.4 mg/kg.

The exploratory meta-analysis produced no clear evidence of an ergogenic effect on any category of outcome. Sport-specific performance, measured as spike performance, did not significantly improve. Nor did physical performance measures including jump height, change of direction, handgrip strength and power output. Physiological outcomes covering fatigue-related and heart-rate-related parameters were likewise unchanged, with all comparisons failing to reach statistical significance. Methodological quality of the individual studies was rated high overall, though some risk of bias was identified, and the GRADE assessment placed the overall certainty of evidence at very low. Caffeine intake was associated with potential adverse effects including hand tremors, anxiety and excessive stimulation.

This complicates rather than overturns the caffeine consensus. Previous meta-analyses in volleyball reported benefits, but drew on male or mixed samples, so this is the first attempt to isolate the female evidence — and it finds the base too thin to support confident claims. Five studies and 66 athletes is a small foundation, and a null result in a small dataset is not the same as demonstrated absence of effect. The very low GRADE certainty means the true effect could still lie in either direction. Larger, women-specific trials, and attention to dose and menstrual cycle phase, are the obvious next steps.

This is a reason to hold the assumption that caffeine reliably sharpens explosive performance more loosely, at least where female volleyball players are concerned. The absence of a clear benefit here reflects a genuinely sparse evidence base as much as it reflects caffeine's physiology, and the authors are explicit that their findings should be treated as preliminary and exploratory rather than a basis for practical recommendations. The reported side effects — tremor, anxiety and over-stimulation — are worth knowing about, particularly in a sport that demands fine motor control. The broader lesson is how much sports nutrition evidence still rests on studies of men.