Effects of Caffeine and Menstrual Phase on Performance of Female Athletes during Heat Stress

The effects of menstrual phase on athletic performance are controversial, but commonly ascribed to temperature-related impairments in physical and cognitive performances. Caffeine stimulates the CNS to enhance endurance performance, and while effects persist for men exercising in the heat, little work has been done with women. Moreover, many female athletes use oral contraceptive steroids (OCS) to regulate their menstrual cycles, which may pronounce the effects of caffeine. The purpose of this study was to evaluate the effects of menstrual phase and caffeine supplementation on physical and cognitive performances of women exercising in the heat. Six recreationally active female subjects (20.3 ± 1.6 yr, 1.67 ± 0.05 m, 69.3 ± 5.5 kg, 49.8 ± 3.3 ml·kg−1·min−1) concurrently taking monophasic OCS volunteered for this study. Each subject completed four trials: in the early follicular (EF, days 3–5) and midfollicuar (MF, days 19–21) phases of the menstrual cycle, after administration of either a placebo (P, corn ...