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Sex differences in the physiological adaptations to heat acclimation: a state-of-the-art review

Abstract

Over the last few decades, females have significantly increased their participation in athletic competitions and occupations (e.g. military, firefighters) in hot and thermally challenging environments. Heat acclimation, which involves repeated passive or active heat exposures that lead to physiological adaptations, is a tool commonly used to optimize performance in the heat. However, the scientific community’s understanding of adaptations to heat acclimation are largely based on male data, complicating the generalizability to female populations. Though limited, current evidence suggests that females may require a greater number of heat acclimation sessions or greater thermal stress to achieve the same magnitude of physiological adaptations as males. The underlying mechanisms explaining the temporal sex differences in the physiological adaptations to heat acclimation are currently unclear. Therefore, the aims of this state-of-the-art review are to: (i) present a brief yet comprehensive synthesis of the current female and sex difference literature, (ii) highlight sex-dependent (e.g. anthropometric, menstrual cycle) and sex-independent factors (e.g. environmental conditions, fitness) influencing the physiological and performance adaptations to heat acclimation, and (iii) address key avenues for future research.

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Abbreviations

E max :

Maximum evaporative capacity of the environment

E req :

Evaporative heat-loss requirement

HA:

Heat acclimation

HR:

Heart rate

HSP:

Heat shock proteins

HSP72:

Heat shock protein 72

MTHA:

Medium-term heat acclimation

LTHA:

Long-term heat acclimation

RH:

Relative humidity

SR:

Sweat rate

STHA:

Short-term heat acclimation

T core :

Core temperature

T skin :

Skin temperature

\(\dot{V}{\text{O}}_{{2{\text{max}}}}\) :

Maximal oxygen uptake

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Funding

This research was supported by the Natural Science and Engineering Research Council of Canada (NSERC) through a Canada Graduate Scholarship—Doctoral (KAW), Postgraduate Scholarship—Doctoral (PJW), and Discovery Grant (SSC, 2018-04077). KAW and PJW were also supported by Brock University Research Training Awards.

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Authors

Contributions

KAW conceived the review topic. KAW, PJW and SSC designed the review, drafted and revised the manuscript. All authors approved the final version of the manuscript.

Corresponding author

Correspondence to Stephen S. Cheung.

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Conflicts of interest

KAW, PJW, SSC all have no conflicts of interest to declare.

Additional information

Communicated by Michael Lindinger.

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Wickham, K.A., Wallace, P.J. & Cheung, S.S. Sex differences in the physiological adaptations to heat acclimation: a state-of-the-art review. Eur J Appl Physiol 121, 353–367 (2021). https://doi.org/10.1007/s00421-020-04550-y

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  • DOI: https://doi.org/10.1007/s00421-020-04550-y

Keywords

  • Heat acclimation
  • Sex differences
  • Thermal load
  • Heat stress
  • Thermal physiology