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

Abstract

Key points One in two female athletes chronically take a combined, monophasic oral contraceptive pill (OCP). Previous thermoregulatory investigations proposed that an endogenous rhythm of the menstrual cycle still occurs with OCP usage. Forthcoming large international sporting events will expose female athletes to hot environments differing in their thermal profile, yet few data exist on how trained women will respond from both a thermoregulatory and performance stand‐point. In the present study, we have demonstrated that a small endogenous rhythm of the menstrual cycle still affects Tcore and also that chronic OCP use attenuates the sweating response, whereas behavioural thermoregulation is maintained. Furthermore, humid heat affects both performance and thermoregulatory responses to a greater extent than OCP usage and the menstrual cycle does. Abstract We studied thermoregulatory responses of ten well‐trained (V̇O2 max , 57 ± 7 mL min−1 kg−1) women taking a combined, monophasic oral contraceptive pill (OCP) (≥12 months) during exercise in dry and humid heat, across their active OCP cycle. They completed four trials, each of resting and cycling at fixed intensities (125 and 150 W), aiming to assess autonomic regulation, and then a self‐paced intensity (30‐min work trial) to assess behavioural regulation. Trials were conducted in quasi‐follicular (qF) and quasi‐luteal (qL) phases in dry (DRY) and humid (HUM) heat matched for wet bulb globe temperature (WBGT) (27°C). During rest and exercise at 125 W, rectal temperature was 0.15°C higher in qL than qF (P = 0.05) independent of environment (P = 0.17). The onset threshold and thermosensitivity of local sweat rate and forearm blood flow relative to mean body temperature was unaffected by the OCP cycle (both P > 0.30). Exercise performance did not differ between quasi‐phases (qF: 268 ± 31 kJ, qL: 263 ± 26 kJ, P = 0.31) but was 5 ± 7% higher during DRY than during HUM (273 ± 29 kJ, 258 ± 28 kJ; P = 0.03). Compared to matched eumenorrhoeic athletes, chronic OCP use impaired the sweating onset threshold and thermosensitivity (both P < 0.01). In well‐trained, OCP‐using women exercising in the heat: (i) a performance‐thermoregulatory trade‐off occurred that required behavioural adjustment; (ii) humidity impaired performance as a result of reduced evaporative power despite matched WBGT; and (iii) the sudomotor but not behavioural thermoregulatory responses were impaired compared to matched eumenorrhoeic athletes.

Individual Responses to Heat Stress: Implications for Hyperthermia and Physical Work Capacity

“…Based on a recent analysis, the weight of the evidence suggests that menstrual phase does alter the T c onset thresholds for sweating and vasodilation, with delays up to 0.5 • C in the luteal phase compared with the follicular phase (Charkoudian et al, 2014). Of note, mild rises in T c have been shown in the luteal phase with combined use of oral contraceptives (Lei et al, 2019). However, measurement of onset thresholds need to be conducted under well-controlled conditions, since their effects are quite small and can be negated by other factors, such as time of day (Stephenson and Kolka, 1985).…”

Heat alleviation strategies for athletic performance: A review and practitioner guidelines

“…The majority of the literature describing chronic heat alleviation techniques is collected in male participants, and accordingly, this raises doubts as to the confidence with which these findings can be directly applied to females. Recent work has begun to address the disparity in data examining sex-specific responses to HA as it is known that oral contraceptive users likely have an altered sweat response [179] and there are notional effects of estrogen on the HSP response [180]; both hallmark adaptations of HA [27,143]. In a study examining the magnitude and temporal patterning of HA between males and females using an isothermic HA protocol [110], it was noted that while STHA may be effective in achieving partial adaptation in females, females require LTHA to establish reductions in cardiovascular and thermoregulatory strain that are comparable to males.…”

Female Sex Hormone Effects on the Vasculature: Considering the Validity of Restricting Study Inclusion to Low-Hormone Phases

“…The luteal phase of the MC is associated with an approximate 0.5°C increase in core temperature (Stephenson and Kolka, 1999); however, female sex hormone concentrations do not appear to alter thermoregulatory effector responses (skin blood flow, sweat rate, etc.) (Charkoudian and Johnson, 1997;Gagnon and Kenny, 2012;Amano et al, 2017;Lei et al, 2019).…”