Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms

Abstract

Physiological strain during exercise is increased by mild dehydration (~1-3% body mass loss). This response may be sex-dependent but there are no direct comparative data in this regard. This review aimed to develop a framework for future research by exploring the potential impact of sex on thermoregulatory and cardiac strain associated with exercise-induced dehydration. Sex-based comparisons were achieved by comparing trends from studies that implemented similar experimental protocols but recruited males and females separately. This revealed a higher core temperature (Tc) in response to exercise-induced dehydration in both sexes, however it seemingly occurred at a lower percent body mass loss in females. Although less clear, similar trends existed for cardiac strain. The average female may have a lower body water volume per body mass compared to males, and therefore the same % body mass loss between the sexes may represent a larger portion of total body water in females potentially posing a greater physiological strain. Additionally, the rate which Tc increases at exercise onset might be faster in females and induce a greater thermoregulatory challenge earlier into exercise. The Tc response at exercise onset is associated with lower sweating rates in females, which is commonly attributed to sex-differences in metabolic heat production. However, a reduced sweat gland sensitivity to stimuli, lower fluid output per sweat gland, and sex hormones promoting fluid retention in females may also contribute. In conclusion, the limited evidence suggests sex-based differences exist in thermoregulatory and cardiac strain associated with exercise-induced dehydration, and this warrants future investigations.

Sex differences in thermoregulation in mammals: Implications for energy homeostasis

“…On average, women have more sweat glands and higher sweat gland density than men ( 96 ). However, during passive and exercise heat stress, women exhibit a lower sweating rate than men ( 97 , 98 ). Evidence suggest that sweat glands in women have a lower frequency and amount of sweat excretion than men ( 97 ), which may be due to lower acetylcholine-induced sweating responses ( 99 ).…”

A Randomized Controlled Trial of Changes in Fluid Distribution across Menstrual Phases with Creatine Supplementation

“…The osmotic effect of the Cr monohydrate is well-documented in terms of ICF increases seen with Cr loading protocols. Nearly 60% of TBW is held intra-cellularly [ 36 ], citing a Cr-directed increase in osmotic pressure as the driver behind cellular swelling and ICF increases [ 17 ]. This is consistent with available studies in male only populations, with significant ICF increases seen in short-term Cr loading protocols ranging from 0.77 L ( p < 0.001) [ 31 ] to ~1.60 L [ 15 , 21 ].…”

Transepidermal water loss and stratum corneum hydration in forearm versus hand palm

“…It is known that in response to assessment procedures of various types there may be increased electrodermal activity reflective of increased hand eccrine gland activation 32 . There is also some limited evidence of reduced sweating rates in females that might be linked to lower sweat gland sensitivity or reduced sweat production per gland 33 . However, it is unclear if there is a gender differential in either palmer sweat gland density or response that could explain the present male‐female difference since no reports of direct gender comparisons have been located.…”