Sex modulates whole‐body sudomotor thermosensitivity during exercise

Abstract

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.Abstract 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 (V O 2 max ) 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%V O 2 max , 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 (R 2 = 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.

Do Heat Events Pose a Greater Health Risk for Individuals with Type 2 Diabetes?

“…49 Decrements in skin blood flow and sweating may not occur at a uniform rate over the entire body and can vary between individuals of similar age. 50 Within the diabetes population the response is heterogeneous.…”

Repeatability of a running heat tolerance test

“…Female participants (n ¼5) taking oral contraceptive performed the experimental sessions during the no pill phase of oral contraceptive use. These timings were selected as they have been shown to be effective in controlling for hormonal fluctuations (Gagnon and Kenny, 2011). Twenty four hours prior to conducting the trials participants were instructed to maintain normal hydration and refrain from the consumption of alcohol, and exhaustive exercise.…”

Sex differences in postsynaptic sweating and cutaneous vasodilation

“…Furthermore, these sex differences only become evident above a certain requirement for heat loss and are solely attributed to a lower sweat gland output in females (10). In contrast, cutaneous blood flow (onset and thermosensitivity) does not differ between males and females during exercise in the heat (10,11).…”

“…sweat gland; skin blood flow; temperature regulation; thermoregulation SEX DIFFERENCES IN TEMPERATURE regulation during exercise exist irrespective of confounding differences in metabolic heat production and physical characteristics. Specifically, females exhibit a lower increase in both local (10) and whole body (10,11) sudomotor activity as a function of increases in body temperature (i.e., thermosensitivity), with no differences in the onset threshold of these responses. Furthermore, these sex differences only become evident above a certain requirement for heat loss and are solely attributed to a lower sweat gland output in females (10).…”