The Influence of Menstrual Cycle Phase on the Physiological and Perceptual Responses to Low-Intensity Continuous and...

The influence of the menstrual cycle (MC) on the acute responses to endurance training remains unclear. This study aimed to investigate the effect of the MC on the physiological and perceptual responses to standardized low-intenstiy continuous (LIT) and high-intensity interval sessions (HIT). Naturally menstruating endurance-trained women performed a standardized LIT (n = 23) and/or HIT (n = 23) session during the early-follicular (EFP), ovulatory (OP), and mid-luteal (MLP) phases of 2 MCs. Physiological (i.e., oxygen uptake ( $\dot{V}$ O₂), heart rate (HR), and blood lactate concentration (BLa)) and perceptual variables (i.e., rating of perceived exertion (RPE) and mood state) were measured. MC phases were determined using urinary ovulation kits and verified with serum hormone analysis. Non-eumenorrheic MCs were excluded from analysis. During LIT and HIT, ventilation (VE) was higher in MLP than OP (p < 0.001) and BLa was slightly higher in EFP than OP (LIT, p = 0.004, HIT, p = 0.001). During HIT, $\dot{V}$ O₂ (p = 0.025) and HR (p = 0.036) were slightly higher during MLP than OP. RPE was slightly higher in EFP than OP in the LIT (p = 0.036) and HIT (p < 0.001). Vigor (p < 0.001) and tension (p = 0.036) were highest in EFP. No phase by time interactions were observed for any of the outcome variables throughout either session type (p > 0.05). MC phase had a modest effect on several physiological and perceptual measures during LIT and HIT. However, the between-phase differences were small and no clear trends emerged across variables to indicate that the overall demands of a LIT or HIT session would be substantially altered in any one particular MC phase.