Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males

Kevin John; Sayyam Kathuria; Jenny Peel; Joe Page; Robyn Aitkenhead; Aimee Felstead; Shane M. Heffernan; Owen Jeffries; Jamie Tallent; Mark Waldron

doi:10.1007/s00421-024-05460-z

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Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males

Journal article

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Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males

Kevin John, Sayyam Kathuria, Jenny Peel, Joe Page, Robyn Aitkenhead, Aimee Felstead, Shane M. Heffernan, Owen Jeffries, Jamie Tallent and Mark Waldron

European Journal of Applied Physiology, Vol.124, pp.2489-2502

2024

DOI: https://doi.org/10.1007/s00421-024-05460-z

PMCID: PMC11322244

PMID: 38568259

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Abstract

caffeine supplementation

ergogenic

endurance performance

heat

thermoregulation

Purpose Caffeine is a commonly used ergogenic aid for endurance events; however, its efficacy and safety have been questioned in hot environmental conditions. The aim of this study was to investigate the effects of acute caffeine supplementation on cycling time to exhaustion and thermoregulation in the heat. Methods In a double-blind, randomised, cross-over trial, 12 healthy caffeine-habituated and unacclimatised males cycled to exhaustion in the heat (35 °C, 40% RH) at an intensity associated with the thermoneutral gas exchange threshold, on two separate occasions, 60 min after ingesting caffeine (5 mg/kg) or placebo (5 mg/kg). Results There was no effect of caffeine supplementation on cycling time to exhaustion (TTE) (caffeine; 28.5 ± 8.3 min vs. placebo; 29.9 ± 8.8 min, P = 0.251). Caffeine increased pulmonary oxygen uptake by 7.4% (P = 0.003), heat production by 7.9% (P = 0.004), whole-body sweat rate (WBSR) by 21% (P = 0.008), evaporative heat transfer by 16.5% (P = 0.006) and decreased estimated skin blood flow by 14.1% (P < 0.001) compared to placebo. Core temperature was higher by 0.6% (P = 0.013) but thermal comfort decreased by − 18.3% (P = 0.040), in the caffeine condition, with no changes in rate of perceived exertion (P > 0.05). Conclusion The greater heat production and storage, as indicated by a sustained increase in core temperature, corroborate previous research showing a thermogenic effect of caffeine ingestion. When exercising at the pre-determined gas exchange threshold in the heat, 5 mg/kg of caffeine did not provide a performance benefit and increased the thermal strain of participants.

Details

Title: Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males
Authors: Kevin John - University of Canberra
Sayyam Kathuria - Swansea University
Jenny Peel - Swansea University
Joe Page - Swansea University
Robyn Aitkenhead - Swansea University
Aimee Felstead - Swansea University
Shane M. Heffernan - Swansea University
Owen Jeffries - Newcastle University
Jamie Tallent - University of Essex
Mark Waldron (Corresponding Author) - University of the Sunshine Coast, Queensland, School of Health and Behavioural Sciences - Legacy
Publication details: European Journal of Applied Physiology, Vol.124, pp.2489-2502
Publisher: Springer
Date published: 2024
DOI: 10.1007/s00421-024-05460-z
ISSN: 1439-6327
PMID: 38568259; PMC11322244
Copyright note: This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Data Availability: Data are available upon suitable request.
Organisation Unit: School of Health; School of Health and Behavioural Sciences - Legacy
Language: English
Record Identifier: 991016189402621
Output Type: Journal article

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