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Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration.
Am J Hum Biol. 2014 May-Jun; 26(3):311-20.AJ

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 Ta 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.

Authors+Show Affiliations

School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand; Department of Sport, Health and Exercise Science, University of Hull, United Kingdom.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

24469986

Citation

Garrett, A T., et al. "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, vol. 26, no. 3, 2014, pp. 311-20.
Garrett AT, Goosens NG, Rehrer NJ, et al. Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration. Am J Hum Biol. 2014;26(3):311-20.
Garrett, A. T., Goosens, N. G., Rehrer, N. J., Patterson, M. J., Harrison, J., Sammut, I., & Cotter, J. D. (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), 311-20. https://doi.org/10.1002/ajhb.22509
Garrett AT, et al. Short-term Heat Acclimation Is Effective and May Be Enhanced Rather Than Impaired By Dehydration. Am J Hum Biol. 2014 May-Jun;26(3):311-20. PubMed PMID: 24469986.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Short-term heat acclimation is effective and may be enhanced rather than impaired by dehydration. AU - Garrett,A T, AU - Goosens,N G, AU - Rehrer,N J, AU - Patterson,M J, AU - Harrison,J, AU - Sammut,I, AU - Cotter,J D, Y1 - 2014/01/28/ PY - 2013/05/14/received PY - 2014/01/08/revised PY - 2014/01/08/accepted PY - 2014/1/29/entrez PY - 2014/1/29/pubmed PY - 2014/12/31/medline SP - 311 EP - 20 JF - American journal of human biology : the official journal of the Human Biology Council JO - Am. J. Hum. Biol. VL - 26 IS - 3 N2 - UNLABELLED: 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 Ta 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. SN - 1520-6300 UR - https://www.unboundmedicine.com/medline/citation/24469986/Short_term_heat_acclimation_is_effective_and_may_be_enhanced_rather_than_impaired_by_dehydration_ L2 - https://doi.org/10.1002/ajhb.22509 DB - PRIME DP - Unbound Medicine ER -