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Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration

Garrett, A.T.; Goosens, N.G.; Rehrer, N.J.; Patterson, M.J.; Harrison, J.; Sammut, I.; Cotter, J.D.

Authors

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Dr Andrew Garrett A.Garrett@hull.ac.uk
Senior Lecturer in Exercise and Environmental Physiology

N.G. Goosens

N.J. Rehrer

M.J. Patterson

J. Harrison

I. Sammut

J.D. Cotter



Abstract

Most heat acclimation data are from regimes longer than 1 week, and acclimation advice is to prevent dehydration. Objectives: We hypothesized that (i) short-term (5-day) heat acclimation would substantially improve physiological strain and exercise tolerance under heat stress, and (ii) dehydration would provide a thermally independent stimulus for adaptation. Methods: Nine aerobically fit males heat acclimated using controlled-hyperthermia (rectal temperature 38.5°C) for 90 min on 5 days; once euhydrated (EUH) and once dehydrated (DEH) during acclimation bouts. Exercising heat stress tests (HSTs) were completed before and after acclimations (90-min cycling in T a 35°C, 60% RH). Results: During acclimation bouts, [aldosterone] plasma rose more across DEH than EUH (95%CI for difference between regimes: 40-411 pg ml -1 ; P=0.03; n=5) and was positively related to plasma volume expansion (r=0.65; P=0.05), which tended to be larger in DEH (CI: -1 to 10%; P=0.06; n=9). In HSTs, resting forearm perfusion increased more in DEH (by 5.9 ml 100 tissue ml -1 min -1 : -11.5 to -1.0; P=0.04) and end-exercise cardiac frequency fell to a greater extent (by 11 b min -1 : -1 to 22; P=0.05). Hydration-related effects on other endocrine, cardiovascular, and psychophysical responses to HSTs were unclear. Rectal temperature was unchanged at rest but was 0.3°C lower at end exercise (P < 0.01; interaction: P=0.52). Conclusions: Short-term (5-day) heat acclimation induced effective adaptations, some of which were more pronounced after fluid-regulatory strain from permissive dehydration, and not attributable to dehydration effects on body temperature. Am. J. Hum. Biol. 26:311-320, 2014. © 2014 Wiley Periodicals, Inc.

Journal Article Type Article
Publication Date 2014-05
Journal American journal of human biology
Print ISSN 1042-0533
Electronic ISSN 1520-6300
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 26
Issue 3
Pages 311-320
Institution Citation Garrett, A., Goosens, N., Rehrer, N., Patterson, M., Harrison, J., Sammut, I., & Cotter, J. (2014). Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration. American journal of human biology : the official journal of the Human Biology Council, 26(3), 311-320. https://doi.org/10.1002/ajhb.22509
DOI https://doi.org/10.1002/ajhb.22509
Keywords Short-term, Hypohydration, Dehydration, Fluid regulation, Plasma volume
Publisher URL http://onlinelibrary.wiley.com/doi/10.1002/ajhb.22509/abstract
Additional Information Authors' accepted manuscript of article: Garrett, A.T., Goosens, N.G., Rehrer, N.J., Patterson, M.J., Harrison, J., Sammut, I. and Cotter, J.D. (2014), Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration. American journal of human biology, 26: 311–320. ©2014 Wiley Periodicals, Inc.

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