Heat stress impairs exogenous carbohydrate oxidation during prolonged running when maintaining euhydration.

Mougin, L; Horner, M; Edwards, D; Nickels, M; Taylor, L; James, LJ; Mears, SA

Heat stress impairs exogenous carbohydrate oxidation during prolonged running when maintaining euhydration.

Mougin, L Horner, M Edwards, D Nickels, M Taylor, L James, LJ Mears, SA

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Publisher:: American Physiological Society
Publication Type:: Journal Article
Citation:: J Appl Physiol (1985), 2025, 139, (6), pp. 1436-1446
Issue Date:: 2025-12-01

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Field	Value	Language
dc.contributor.author	Mougin, L
dc.contributor.author	Horner, M
dc.contributor.author	Edwards, D
dc.contributor.author	Nickels, M
dc.contributor.author	Taylor, L
dc.contributor.author	James, LJ
dc.contributor.author	Mears, SA
dc.date.accessioned	2026-05-26T03:06:48Z
dc.date.available	2026-05-26T03:06:48Z
dc.date.issued	2025-12-01
dc.identifier.citation	J Appl Physiol (1985), 2025, 139, (6), pp. 1436-1446
dc.identifier.issn	8750-7587
dc.identifier.issn	1522-1601
dc.identifier.uri	http://hdl.handle.net/10453/195132
dc.description.abstract	This study investigated the effect of running in a hot environment compared with a temperate environment on exogenous carbohydrate oxidation, while maintaining a state of euhydration. Ten trained runners (24 ± 6 yr; 72.7 ± 8.3 kg; V̇o2peak: 63 ± 6 mL/kg/min) completed two trials [100 min of steady state running at ∼65% V̇o2peak in either a temperate (19°C; TEMP) or a hot environment (34°C; HOT)]. Water was provided every 20 min to replace ∼90% of body mass losses (TEMP: 0.8 ± 0.2 L; HOT: 1.7 ± 0.4 L). In each trial, participants consumed 60 g/h (bolus every 20 min) of a 35% dextrose solution enriched with [U-13C] glucose (145 ± 2 δ‰ vs. PDB). Expired breath (analyzed for 13C:12C) and blood samples were collected every 20 min during exercise. Average (40-100 min) and peak exogenous carbohydrate oxidation rates were 20% (HOT: 0.43 ± 0.09 vs. TEMP: 0.54 ± 0.12 g/min; P = 0.006) and 18% (HOT: 0.67 ± 0.10 vs. TEMP: 0.81 ± 0.11 g/min; P = 0.002) lower in HOT than in TEMP, respectively. Total carbohydrate oxidation (P = 0.111) was not significantly different between trials, resulting in a greater contribution from endogenous sources in HOT versus TEMP (2.10 ± 0.35 vs. 1.86 ± 0.30 g/min; P = 0.020). Gastrointestinal temperature and heart rate (P < 0.001) were greater in HOT. Even with adequate hydration, running in a hot environment reduced exogenous carbohydrate.NEW & NOTEWORTHY This study showed that exogenous carbohydrate oxidation is reduced by ∼20% during running in the heat, even while controlling fluid intake to maintain euhydration, highlighting that heat stress alone impairs exogenous carbohydrate use. These findings suggest a lower exogenous carbohydrate oxidation and a greater reliance on endogenous stores when exercising in the heat, independently of the effects of dehydration.
dc.format	Print-Electronic
dc.language	eng
dc.publisher	American Physiological Society
dc.relation.ispartof	J Appl Physiol (1985)
dc.relation.isbasedon	10.1152/japplphysiol.00873.2025
dc.rights	info:eu-repo/semantics/openAccess
dc.subject	06 Biological Sciences, 11 Medical and Health Sciences
dc.subject.classification	Physiology
dc.subject.classification	31 Biological sciences
dc.subject.classification	32 Biomedical and clinical sciences
dc.subject.classification	42 Health sciences
dc.subject.mesh	Humans
dc.subject.mesh	Running
dc.subject.mesh	Male
dc.subject.mesh	Oxidation-Reduction
dc.subject.mesh	Adult
dc.subject.mesh	Young Adult
dc.subject.mesh	Hot Temperature
dc.subject.mesh	Carbohydrate Metabolism
dc.subject.mesh	Oxygen Consumption
dc.subject.mesh	Heat-Shock Response
dc.subject.mesh	Heat Stress Disorders
dc.subject.mesh	Glucose
dc.subject.mesh	Dehydration
dc.subject.mesh	Female
dc.subject.mesh	Humans
dc.subject.mesh	Dehydration
dc.subject.mesh	Heat Stress Disorders
dc.subject.mesh	Glucose
dc.subject.mesh	Oxidation-Reduction
dc.subject.mesh	Oxygen Consumption
dc.subject.mesh	Heat-Shock Response
dc.subject.mesh	Running
dc.subject.mesh	Adult
dc.subject.mesh	Female
dc.subject.mesh	Male
dc.subject.mesh	Carbohydrate Metabolism
dc.subject.mesh	Hot Temperature
dc.subject.mesh	Young Adult
dc.subject.mesh	Humans
dc.subject.mesh	Running
dc.subject.mesh	Male
dc.subject.mesh	Oxidation-Reduction
dc.subject.mesh	Adult
dc.subject.mesh	Young Adult
dc.subject.mesh	Hot Temperature
dc.subject.mesh	Carbohydrate Metabolism
dc.subject.mesh	Oxygen Consumption
dc.subject.mesh	Heat-Shock Response
dc.subject.mesh	Heat Stress Disorders
dc.subject.mesh	Glucose
dc.subject.mesh	Dehydration
dc.subject.mesh	Female
dc.title	Heat stress impairs exogenous carbohydrate oxidation during prolonged running when maintaining euhydration.
dc.type	Journal Article
utslib.citation.volume	139
utslib.location.activity	United States
utslib.for	06 Biological Sciences
utslib.for	11 Medical and Health Sciences
pubs.organisational-group	University of Technology Sydney
pubs.organisational-group	University of Technology Sydney/Faculty of Health
utslib.copyright.status	open_access	*
dc.rights.license	This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/
dc.date.updated	2026-05-26T03:06:46Z
pubs.issue	6
pubs.publication-status	Published
pubs.volume	139
utslib.citation.issue	6

Abstract:

This study investigated the effect of running in a hot environment compared with a temperate environment on exogenous carbohydrate oxidation, while maintaining a state of euhydration. Ten trained runners (24 ± 6 yr; 72.7 ± 8.3 kg; V̇o2peak: 63 ± 6 mL/kg/min) completed two trials [100 min of steady state running at ∼65% V̇o2peak in either a temperate (19°C; TEMP) or a hot environment (34°C; HOT)]. Water was provided every 20 min to replace ∼90% of body mass losses (TEMP: 0.8 ± 0.2 L; HOT: 1.7 ± 0.4 L). In each trial, participants consumed 60 g/h (bolus every 20 min) of a 35% dextrose solution enriched with [U-13C] glucose (145 ± 2 δ‰ vs. PDB). Expired breath (analyzed for 13C:12C) and blood samples were collected every 20 min during exercise. Average (40-100 min) and peak exogenous carbohydrate oxidation rates were 20% (HOT: 0.43 ± 0.09 vs. TEMP: 0.54 ± 0.12 g/min; P = 0.006) and 18% (HOT: 0.67 ± 0.10 vs. TEMP: 0.81 ± 0.11 g/min; P = 0.002) lower in HOT than in TEMP, respectively. Total carbohydrate oxidation (P = 0.111) was not significantly different between trials, resulting in a greater contribution from endogenous sources in HOT versus TEMP (2.10 ± 0.35 vs. 1.86 ± 0.30 g/min; P = 0.020). Gastrointestinal temperature and heart rate (P < 0.001) were greater in HOT. Even with adequate hydration, running in a hot environment reduced exogenous carbohydrate.NEW & NOTEWORTHY This study showed that exogenous carbohydrate oxidation is reduced by ∼20% during running in the heat, even while controlling fluid intake to maintain euhydration, highlighting that heat stress alone impairs exogenous carbohydrate use. These findings suggest a lower exogenous carbohydrate oxidation and a greater reliance on endogenous stores when exercising in the heat, independently of the effects of dehydration.

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