Tags

Type your tag names separated by a space and hit enter

Short term heat acclimation reduces heat stress, but is not augmented by dehydration.
J Therm Biol. 2018 Dec; 78:227-234.JT

Abstract

Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg-1 15 min-1, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg-1 15 min-1, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance. Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn. Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ± 0.1-39.0 ± 0.1 °C: P < 0.001) and EUH acclimation (39.5 ± 0.1-38.9 ± 0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ± 0.06-1.89 ± 0.09 L h-1) compared to EUH acclimation (1.57 ± 0.06-1.79 ± 0.08 L h-1: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83). In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation.

Authors+Show Affiliations

Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT, United States.Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT, United States.Department of Health and Human Performance, Montana Center for Work Physiology and Exercise Metabolism, University of Montana, Missoula, MT, United States. Electronic address: charles.dumke@umontana.edu.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

30509641

Citation

Schleh, Michael W., et al. "Short Term Heat Acclimation Reduces Heat Stress, but Is Not Augmented By Dehydration." Journal of Thermal Biology, vol. 78, 2018, pp. 227-234.
Schleh MW, Ruby BC, Dumke CL. Short term heat acclimation reduces heat stress, but is not augmented by dehydration. J Therm Biol. 2018;78:227-234.
Schleh, M. W., Ruby, B. C., & Dumke, C. L. (2018). Short term heat acclimation reduces heat stress, but is not augmented by dehydration. Journal of Thermal Biology, 78, 227-234. https://doi.org/10.1016/j.jtherbio.2018.10.004
Schleh MW, Ruby BC, Dumke CL. Short Term Heat Acclimation Reduces Heat Stress, but Is Not Augmented By Dehydration. J Therm Biol. 2018;78:227-234. PubMed PMID: 30509641.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Short term heat acclimation reduces heat stress, but is not augmented by dehydration. AU - Schleh,Michael W, AU - Ruby,Brent C, AU - Dumke,Charles L, Y1 - 2018/10/19/ PY - 2018/06/29/received PY - 2018/09/21/revised PY - 2018/10/12/accepted PY - 2018/12/5/entrez PY - 2018/12/5/pubmed PY - 2019/1/15/medline KW - Core temperature KW - Heat stress KW - Hypohydration KW - Physiologic strain KW - Plasma volume SP - 227 EP - 234 JF - Journal of thermal biology JO - J. Therm. Biol. VL - 78 N2 - Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg-1 15 min-1, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg-1 15 min-1, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance. Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn. Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ± 0.1-39.0 ± 0.1 °C: P < 0.001) and EUH acclimation (39.5 ± 0.1-38.9 ± 0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ± 0.06-1.89 ± 0.09 L h-1) compared to EUH acclimation (1.57 ± 0.06-1.79 ± 0.08 L h-1: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83). In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation. SN - 0306-4565 UR - https://www.unboundmedicine.com/medline/citation/30509641/Short_term_heat_acclimation_reduces_heat_stress_but_is_not_augmented_by_dehydration_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0306-4565(18)30283-3 DB - PRIME DP - Unbound Medicine ER -