Background: Hormonal fluctuations across the menstrual cycle may influence cognitive and neuromuscular performance in female athletes. Caffeine (CAF) is a widely used ergogenic aid, yet its phase-specific effects remain unclear. This study investigated the acute effects of CAF supplementation on cognitive and physical performance across menstrual cycle phases in eumenorrheic female athletes. Methods: Twelve trained female athletes with regular menstrual cycles participated in a randomized, double-blind, placebo-controlled study. Each participant completed a battery of cognitive (reaction time RT, vigilance test VT) and physical performance tests (countermovement jump CMJ, repeated sprint test RST, and time to exhaustion test TTE) during the early follicular (EFP), late follicular (LFP), and mid-luteal (MLP) phases. CAF (400 mg) or a placebo (PLA) was ingested one hour before the testing session. Results: CAF supplementation significantly improved VT performance across all menstrual cycle phases compared with PLA (p 0.05). Conclusions: CAF supplementation was associated with consistent improvements in vigilance and reaction time across the menstrual cycle. However, effects on neuromuscular performance were less consistent and not clearly phase-dependent. These findings highlight that while CAF can enhance certain aspects of cognitive performance in female athletes, responses in physical performance may vary and require further investigation. CAF may contribute to improvements in selected neuromuscular outcomes, although evidence for phase-specific ergogenic effects remains limited.
Hsen et al. (2026) studied this question.