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MENSTRUAL CYCLE PHASE EFFECTS ON EXERCISE THERMOREGULATION AND PERFORMANCE IN THE HEAT

Abstract

The menstrual cycle (MC) is described as the natural fluctuation of hormones. It is known that the high-hormone luteal phase exhibits higher resting core temperature (Tc) compared to the low-hormone follicular phase. However, research is inconclusive and limited on whether elevated Tc impacts performance during exercise in hot conditions. PURPOSE: To determine if thermoregulatory measures are altered between MC phases, and whether the changes hinder running performance in the heat. METHODS: Recreationally trained, naturally menstruating adults completed two treadmill runs in simulated conditions during contrasting MC phases: early follicular (EF) and midluteal (ML). Subjects ran for 45min at a constant self-selected light pace, followed by a 15min performance test for distance. Environmental chamber was set to 32°C, 40% relative humidity (mean WBGT 31.8±1.6°C). Tc, mean skin temperature (Ts), heart rate (HR), perceived exertion (RPE), thermal perception (THERM), and comfort perception (COMF) were assessed every 5min. Sweat perception (SP), sweat loss (SL), session ratings (sRPE, sTHERM, sCOMF), and performance test distance (DIST) were taken upon trial completion. Blood serum was analyzed for estrogen and progesterone concentrations to confirm MC phases. Two-way (phase X time) repeated measures ANOVAs were run for physiological and perceptual measures. Paired t-tests were run to assess phase differences in session ratings, SP, SL, and distance covered on the performance test. RESULTS: For n=5, Tc, Ts, HR, RPE, THERM, and COMF showed a main effect of time (p<0.001 for all) but no effect of phase (p>0.05 for all). Tc was not significantly different at baseline ([mean and SD] EF: 36.2±1.0℃, ML: 35.6±1.2℃, p=0.42). No significant phase differences were observed for SP (EF: 1094±428ml, ML: 1189±474ml, p=0.45), SL (EF: 1092±310ml, ML: 1159±257ml, p=0.79), sRPE (EF: 14.0±1.4, ML: 14.0±2.0, p=1.00), sTHERM (EF: -2.4±0.5, ML: -3.4±0.5, p=0.06), sCOMF (EF: 2.8±0.4, ML: 3.4±0.9, p=0.18), or DIST (EF: 1.71±0.32mi, ML: 1.70±0.45mi, p=0.96). CONCLUSION: MC phase does not appear to influence measures of thermoregulation or exercise performance in the heat. Athletes may continue to exercise per usual without concern of MC phase effects.

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