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Human tolerance to heat strain during exercise: influence of hydration.
J Appl Physiol (1985). 1992 Jul; 73(1):368-75.JA

Abstract

This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a given level of physiological strain. Seventeen heat-acclimated men [maximal oxygen uptake (VO2max) from 45 to 65 ml.kg-1.min-1] attempted two heat stress tests (HSTs): one when euhydrated and one when hypohydrated by 8% of total body water. The HSTs consisted of 180 min of rest and treadmill walking (45% VO2max) in a hot-dry (ambient temperature 49 degrees C, relative humidity 20%) environment. The required evaporative cooling (Ereq) exceeded the maximal evaporative cooling capacity of the environment (Emax); thus thermal equilibrium could not be achieved and 27 of 34 HSTs ended by exhaustion from heat strain. Our findings concerning exhaustion from heat strain are 1) hypohydration reduced the core temperature that could be tolerated; 2) aerobic fitness, per se, did not influence the magnitude of heat strain that could be tolerated; 3) curves can be developed to estimate exhaustion rates for a given level of physiological strain; and 4) exhaustion was rarely associated with a core temperature up to 38 degrees C, and it always occurred before a temperature of 40 degrees C was achieved. These findings are applicable to heat-acclimated individuals performing moderate-intensity exercise under conditions where Ereq approximates or exceeds Emax and who have high skin temperatures.

Authors+Show Affiliations

US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

1506393

Citation

Sawka, M N., et al. "Human Tolerance to Heat Strain During Exercise: Influence of Hydration." Journal of Applied Physiology (Bethesda, Md. : 1985), vol. 73, no. 1, 1992, pp. 368-75.
Sawka MN, Young AJ, Latzka WA, et al. Human tolerance to heat strain during exercise: influence of hydration. J Appl Physiol (1985). 1992;73(1):368-75.
Sawka, M. N., Young, A. J., Latzka, W. A., Neufer, P. D., Quigley, M. D., & Pandolf, K. B. (1992). Human tolerance to heat strain during exercise: influence of hydration. Journal of Applied Physiology (Bethesda, Md. : 1985), 73(1), 368-75.
Sawka MN, et al. Human Tolerance to Heat Strain During Exercise: Influence of Hydration. J Appl Physiol (1985). 1992;73(1):368-75. PubMed PMID: 1506393.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Human tolerance to heat strain during exercise: influence of hydration. AU - Sawka,M N, AU - Young,A J, AU - Latzka,W A, AU - Neufer,P D, AU - Quigley,M D, AU - Pandolf,K B, PY - 1992/7/1/pubmed PY - 1992/7/1/medline PY - 1992/7/1/entrez SP - 368 EP - 75 JF - Journal of applied physiology (Bethesda, Md. : 1985) JO - J Appl Physiol (1985) VL - 73 IS - 1 N2 - This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a given level of physiological strain. Seventeen heat-acclimated men [maximal oxygen uptake (VO2max) from 45 to 65 ml.kg-1.min-1] attempted two heat stress tests (HSTs): one when euhydrated and one when hypohydrated by 8% of total body water. The HSTs consisted of 180 min of rest and treadmill walking (45% VO2max) in a hot-dry (ambient temperature 49 degrees C, relative humidity 20%) environment. The required evaporative cooling (Ereq) exceeded the maximal evaporative cooling capacity of the environment (Emax); thus thermal equilibrium could not be achieved and 27 of 34 HSTs ended by exhaustion from heat strain. Our findings concerning exhaustion from heat strain are 1) hypohydration reduced the core temperature that could be tolerated; 2) aerobic fitness, per se, did not influence the magnitude of heat strain that could be tolerated; 3) curves can be developed to estimate exhaustion rates for a given level of physiological strain; and 4) exhaustion was rarely associated with a core temperature up to 38 degrees C, and it always occurred before a temperature of 40 degrees C was achieved. These findings are applicable to heat-acclimated individuals performing moderate-intensity exercise under conditions where Ereq approximates or exceeds Emax and who have high skin temperatures. SN - 8750-7587 UR - https://www.unboundmedicine.com/medline/citation/1506393/Human_tolerance_to_heat_strain_during_exercise:_influence_of_hydration_ L2 - https://journals.physiology.org/doi/10.1152/jappl.1992.73.1.368?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -