Influence of menstrual phase and arid vs. humid heat stress on autonomic and behavioural thermoregulation during exercise in trained but unacclimated women

Abstract

Key pointsr Despite an attenuated fluctuation in ovarian hormone concentrations in well-trained women, one in two of such women believe their menstrual cycle negatively impacts training and performance.r Forthcoming large international events will expose female athletes to hot environments, and studies evaluating aerobic exercise performance in such environments across the menstrual cycle are sparse, with mixed findings.r We have identified that autonomic heat loss responses at rest and during fixed-intensity exercise in well-trained women are not affected by menstrual cycle phase, but differ between dry and humid heat.r Furthermore, exercise performance is not different across the menstrual cycle, yet is lower in humid heat, in conjunction with reduced evaporative cooling.r Menstrual cycle phase does not appear to affect exercise performance in the heat in well-trained women, but humidity impairs performance, probably due to reduced evaporative power. AbstractWe studied thermoregulatory responses of ten well-trained [VO 2max , 57 (7) ml min −1 kg −1 ] eumenorrheic women exercising in dry and humid heat, across their menstrual cycle. They completed four trials, each of resting and cycling at fixed intensities (125 and 150 W), to assess autonomic regulation, then self-paced intensity (30 min work trial), to assess behavioural regulation. Trials were in early-follicular (EF) and mid-luteal (ML) phases in dry (DRY) and humid (HUM) heat matched for wet bulb globe temperature (WBGT, 27°C). During rest and fixed-intensity exercise, rectal temperature was ß0.2°C higher in ML than EF (P < 0.01) independent of environment (P = 0.66). Mean skin temperature did not differ between menstrual phases (P ࣙ 0.13) but was higher in DRY than HUM (P < 0.01). Local sweat rate and/or forearm blood flow differed as a function of menstrual phase and environment (interaction: P ࣘ 0.01). Exercise performance did not differ between phases [EF: 257 (37), ML: 255 (43) kJ, P = 0.62], but was 7 (9)% higher in DRY than HUM [263 (39), 248 (40) kJ; P < 0.01] in conjunction with equivalent autonomic regulation and thermal strain but higher evaporative cooling [16 (6) W m 2 ; P < 0.01]. In well-trained women exercising in the heat: (1) menstrual phase did not affect performance, (2) humidity impaired performance due to reduced evaporative cooling despite matched WBGT and (3) behavioural responses nullified thermodynamic and autonomic differences associated with menstrual phase and dry vs. humid heat. Abbreviations BP, blood pressure; BSA, body surface area; C, rate of heat transfer from convection; C res , rate of respiratory conductive heat transfer; E, rate of evaporative heat loss; EF, early follicular; E max , maximal evaporative capacity of the environment; E req , required evaporative cooling for heat balance; E res , rate of respiratory evaporative heat transfer; FBF, forearm blood flow; FVR, forearm vascular resistance; h c , convective heat transfer coefficient; HR, heart rate; HSI, heat strain index; IAAF, International Association of At...

On exercise thermoregulation in females: interaction of endogenous and exogenous ovarian hormones

“…The data of the eumenorrhoeic group have been reported previously with respect to testing unique aims and hypotheses (Lei et al . ). The training history for both OCP and eumenorrhoeic groups was similar at 5 ± 3 years (range 2–12 years).…”

“…The present study replicated all of the conditions used for our matched eumenorrhoeic group (Lei et al . ). All trials were conducted during autumn to spring in Palmerston North, New Zealand, when temperatures rarely exceed 22°C.…”

“…This eases the required evaporation and decreases thermoregulatory strain to the point where the menstrual phase‐related thermodynamic and autonomic differences become nullified (Lei et al . ). Furthermore, these menstrual phase‐related effects were relatively small in well‐trained women.…”

“…Therefore, a secondary objective was to compare the results of the current OCP cohort matched in relevant physical and fitness characteristics with those of our previous eumenorrhoeic cohort (Lei et al . ).…”

“…In our previous investigation, the performance of eumenorrhoeic athletes was impaired in humid compared to dry ambient heat matched for wet bulb globe temperature (WBGT) (27 °C) (Lei et al . ). To our knowledge, no previous study has compared thermoregulatory and performance responses in women taking OCP when exposed to humid vs .…”