Whole-body heat exchange in women during constant- and variable-intensity work in the heat
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ORIGINAL ARTICLE
Whole‑body heat exchange in women during constant‑ and variable‑intensity work in the heat Sean R. Notley1 · Andrew W. D’Souza1 · Robert D. Meade1 · Brodie J. Richards1 · Glen P. Kenny1 Received: 9 July 2020 / Accepted: 27 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Time-weighted averaging is used in occupational heat stress guidelines to estimate the metabolic demands of variable-intensity work. However, compared to constant-intensity work of the same time-weighted average metabolic rate, variable-intensity work may cause decrements in total heat loss (dry + evaporative heat loss) that exacerbate heat storage in women. We therefore used direct calorimetry to assess whole-body total heat loss and heat storage (metabolic heat production minus total heat loss) in women and men during constant- and variable-intensity work of equal average intensity. Methods Ten women [mean (SD); 31 (11) years] and fourteen men [30 (8) years] completed two trials involving 90-min of constant- and variable-intensity work (cycling) eliciting an average metabolic heat production of ~ 200 W/m2 in dryheat (40 °C, ~ 15% relative humidity). External work was fixed at ~ 40 W/m2 for constant-intensity work, and alternated between ~ 15 and ~ 60 W/m2 (5-min each) for variable-intensity work. Results When expressed as a time-weighted average over each work period, total heat loss did not differ between men and women (mean difference [95% CI]; 4 W/m2 [− 11, 20]; p = 0.572) or between constant- and variable-intensity work (1 W/ m2 [− 3, 5]; p = 0.642). Consequently, heat storage did not differ significantly between men and women (− 4 W/m2 [− 17, 8]; p = 0.468) or between constant- and variable-intensity work (0 W/m2 [− 3, 3]; p = 0.834). Conclusion Neither whole-body heat loss nor heat storage was modulated by the partitioning of work intensity, indicating that time-weighted averaging is appropriate for estimating metabolic demand to assess occupational heat stress in women. Keywords Calorimetry · Heat exchange · Heat strain · Sex · Work Abbreviations AD Body surface area CON Constant-intensity work DHL Dry heat loss EHL Evaporative heat loss Ereq Evaporative requirement for heat loss HR Heart rate Tre Rectal temperature Tsk Mean skin temperature LBM Lean body mass LSR Local sweat rate Communicated by Narihiko Kondo. * Glen P. Kenny [email protected] 1
Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, 125 University Private, Room 367 Montpetit Hall, Ottawa, ON K1N 6N5, Canada
M-W Metabolic heat production VAR Variable-intensity work ̇ 2 peak Peak oxygen consumption VO WBSR Whole-body sweat rate
Introduction Occupational heat stress is a common physical hazard affecting millions of employees (Flouris et al. 2018). To prevent rises in core temperature (≥ 38 °C) that may compromise health (WHO 1969), occupational safety institutes recommend heat stress limits defined by the environmental conditions and the est
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