Do E2 and P4 contribute to the explained variance in core temperature response for trained women during exertional heat stress when metabolic rates are very high?

Purpose Women remain underrepresented in the exercise thermoregulation literature despite their participation in leisuretime and occupational physical activity in heat-stressful environments continuing to increase. Here, we determined the relative contribution of the primary ovarian hormones (estrogen [E-2] and progesterone [P-4]) alongside other morphological (e.g., body mass), physiological (e.g., sweat rates), functional (e.g., aerobic fitness) and environmental (e.g., vapor pressure) factors in explaining the individual variation in core temperature responses for trained women working at very high metabolic rates, specifically peak core temperature (T-peak) and work output (mean power output). Methods Thirty-six trained women (32 +/- 9 year, 53 +/- 9 ml.kg(-1).min(-1)), distinguished by intra-participant (early follicular and mid-luteal phases) or inter-participant (ovulatory vs. anovulatory vs. oral contraceptive pill user) differences in their endogenous E-2 and P-4 concentrations, completed a self-paced 30-min cycling work trial in warm-dry (2.2 +/- 0.2 kPa, 34.1 +/- 0.2 degrees C, 41.4 +/- 3.4% RH) and/or warm-humid (3.4 +/- 0.1 kPa, 30.2 +/- 1.2 degrees C, 79.8 +/- 3.7% RH) conditions that yielded 115 separate trials. Stepwise linear regression was used to explain the variance of the dependent variables. Results Models were able to account for 60% of the variance in T-peak ((R) over bar (2) : 41% core temperature at the start of work trial, (R) over bar (2) : 15% power output, (R) over bar (2) : 4% [E-2]) and 44% of the variance in mean power output ((R) over bar (2) : 35% peak aerobic power, (R) over bar (2) : 9% perceived exertion). Conclusion E-2 contributes a small amount toward the core temperature response in trained women, whereby starting core temperature and peak aerobic power explain the greatest variance in T-peak and work output, respectively.