Sex modulates whole‐body sudomotor thermosensitivity during exercise

• Published in: The Journal of physiology Vol. 589; no. 24; pp. 6205 - 6217
• Main Authors: Gagnon, Daniel, Kenny, Glen P.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 15.12.2011; Wiley Subscription Services, Inc; Blackwell Science Inc
• Subjects: Adult; Body Temperature - physiology; Body Temperature Regulation - physiology; Calorimetry; Estradiol - blood; Exercise - physiology; Female; Humans; Integrative; Male; Oxygen Consumption; Progesterone - blood; Sex Factors; Sweating - physiology; Young Adult
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2011.219220

Non‐technical summary  The human body controls its temperature through coordinated physiological processes. Prior to the current study, it remained unknown if differences between males and females existed in these processes. The results from the current study show that females have a lower whole‐body sweat response during exercise in the heat compared to males, which results in a greater increase in body temperature. The physiological process responsible for the lower whole‐body sweat rate was a lower thermosensitivity of the response, meaning a lower increase in sweat production for a given increase in body temperature. Knowledge of sex‐related differences in the physiology of temperature regulation may lead to better improvements in heat exposure guidelines for industrial, military and athletic settings.   It is unclear whether true physiological differences exist in temperature regulation between males and females during exercise, independently of differences in physical characteristics and metabolic heat production. Therefore, we examined differences in the onset threshold and thermosensitivity of whole‐body sudomotor activity and cutaneous vascular conductance between males and females matched for body mass and surface area. Nine males and nine females performed 90 min of exercise at each of the following intensities in a warm/dry environment: 50% of maximum oxygen consumption () and at a fixed rate of metabolic heat production equal to 500 W. Evaporative heat loss (EHL, direct calorimetry) and cutaneous vascular conductance (CVC, laser‐Doppler) were measured continuously. Mean body temperature was calculated from the measurements of oesophageal and mean skin temperatures. During exercise at 50%, a lower rate of sudomotor activity was observed in females (385 ± 12 vs. 512 ± 24 W, P < 0.001). However, irrespective of sex, individual EHL values were strongly associated with metabolic heat production (R2= 0.82, P < 0.001). Nonetheless, a lower rate of EHL was observed in females when exercise was performed at 500 W of metabolic heat production (419 ± 7 vs. 454 ± 11 W, P= 0.032). Furthermore, a lower increase in EHL per increase in mean body temperature was observed in females (553 ± 77 vs. 795 ± 85 W °C−1, P= 0.051), with no differences in the onset threshold (36.77 ± 0.06 vs. 36.61 ± 0.11°C, P= 0.242). In contrast, no differences were observed in CVC. Collectively, these findings demonstrate that females have a lower thermosensitivity of the whole‐body sudomotor response compared to males during exercise in the heat performed at a fixed rate of metabolic heat production.