Menstrual Phase–Specific Effects of Caffeine Supplementation on Cognitive Function and Neuromuscular Performance in Eumenorrheic Female Athletes

Background: Hormonal fluctuations across the menstrual cycle may influence cognitive and neuromuscular performance in female athletes. Caffeine is a widely used ergogenic aid, yet its phase-specific effects remain unclear. This study investigated the acute effects of caffeine supplementation on cognitive and physical performance across menstrual cycle phases in eumenorrheic female athletes. Methods: Twelve trained female athletes (mean age: 24.4 ± 2.7 years) 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. Caffeine (CAF) (400 mg) or placebo (PLA) was ingested one hour before the testing session. Results: CAF significantly improved vigilance performance across all menstrual phases compared with placebo (p<0.01), with no phase effect (p=0.26). RT score was significantly reduced following CAF ingestion during the LFP (p=0.02) and MLP (p<0.01), whereas no significant effect was observed during the EFP (p=0.22). Regarding CMJ, in the PLA condition, jump height was higher during the LFP than EFP and MLP (p<0.01), while CAF significantly increased jump performance during the MLP compared with PLA condition (p<0.01). During repeated sprint exercise, peak power declined across sprints (p<0.01); however, CAF significantly increased peak power output (p=0.02), particularly during later sprints in the MLP (p<0.05). Time-to-exhaustion was not influenced by CAF or menstrual phase (p>0.48). Conclusion: CAF supplementation consistently enhances cognitive performance across the menstrual cycle and selectively improves neuromuscular performance during the mid-luteal phase, supporting its targeted ergogenic use to mitigate menstrual phase–related performance fluctuations in female athletes.