Effects of Caffeine Supplementation on Cognitive Function and Neuromuscular Performance Across Menstrual Cycle Phases in Eumenorrheic Female Athletes: A Randomized, Double-Blind Placebo-Controlled Pilot Trial

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), with no phase-dependent effect. RT was significantly reduced following CAF ingestion (p < 0.05), with no significant condition × phase interaction. CMJ performance varied across menstrual phases under placebo conditions, with higher values observed during the LFP (p < 0.05); a trend toward enhanced jump performance was observed following CAF ingestion, particularly during the MLP. During RST, performance declined across sprints in all conditions (p < 0.05), and CAF supplementation attenuated fatigue-related performance declines during later sprints, irrespective of menstrual cycle phase. Time to exhaustion was not significantly influenced by CAF supplementation or menstrual cycle phase (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.