Heat Acclimation Does Not Modify  Q 10  and Thermal Cardiac Reactivity

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Abstract

Heat acclimation (HA) is an essential modifier of physiological strain when working or exercising in the heat. It is unknown whether HA influences the increase of energy expenditure ( Q ₁₀ effect) or heart rate (thermal cardiac reactivity TCR) due to increased body temperature. Therefore, we studied these effects using a heat strain database of climatic chamber experiments performed by five semi-nude young males in either non-acclimated or acclimated state. Measured oxygen consumption rate (VO ₂), heart rate (HR), and rectal temperature ( T _re) averaged over the third hour of exposure were obtained from 273 trials in total. While workload (walking 4 km/h on level) was constant, heat stress conditions varied widely with air temperature 25–55°C, vapor pressure 0.5–5.3 kPa, and air velocity 0.3–2 m/s. HA was induced by repeated heat exposures over a minimum of 3 weeks. Non-acclimated experiments took place in wintertime with a maximum of two exposures per week. The influence of T _re and HA on VO ₂ and HR was analyzed separately with mixed model ANCOVA. Rising T _re significantly ( p < 0.01) increased both VO ₂ (by about 7% per degree increase of T _re) and HR (by 39–41 bpm per degree T _re); neither slope nor intercept depended significantly on HA ( p > 0.4). The effects of T _re in this study agree with former outcomes for VO ₂ (7%/°C increase corresponding to Q ₁₀ = 2) and for HR (TCR of 33 bpm/°C in ISO 9886). Our results indicate that both relations are independent of HA with implications for heat stress assessment at workplaces and for modeling heat balance.

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Author and article information

Contributors

Bernhard Kampmann: URI : https://loop.frontiersin.org/people/781145/overview

Peter Bröde: URI : https://loop.frontiersin.org/people/774546/overview

Journal

Journal ID (nlm-ta): Front Physiol

Journal ID (iso-abbrev): Front Physiol

Journal ID (publisher-id): Front. Physiol.

Title: Frontiers in Physiology

Publisher: Frontiers Media S.A.

ISSN (Electronic): 1664-042X

Publication date (Electronic): 17 December 2019

Publication date Collection: 2019

Volume: 10

Electronic Location Identifier: 1524

Affiliations

[1] ¹Department of Occupational Health Science, School of Mechanical Engineering and Safety Engineering, University of Wuppertal , Wuppertal, Germany

[2] ²Department of Immunology, Leibniz Research Centre for Working Environment and Human Factors (IfADo) , Dortmund, Germany

Author notes

Edited by: Andrew T. Garrett, University of Hull, United Kingdom

Reviewed by: Michal Horowitz, Hebrew University of Jerusalem, Israel; Fabien Andre Basset, Memorial University of Newfoundland, Canada

*Correspondence: Peter Bröde, broede@ 123456ifado.de

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Article

DOI: 10.3389/fphys.2019.01524

PMC ID: 6929604

SO-VID: fdde747f-4271-45d1-8966-a9fd92e23986

License:

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

History

Date received : 28 July 2019

Date accepted : 04 December 2019

Page count

Figures: 2, Tables: 1, Equations: 2, References: 43, Pages: 6, Words: 4230

Funding

Funded by: Open Access Fund of the Leibniz Association

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