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Heat acclimation does not affect maximal aerobic power in thermoneutral normoxic or hypoxic conditions
Jozef Stefan Institute, Ljubljana. (Department of Robotics and Biocybernetics)
Jozef Stefan Institute, Ljubljana. (Department of Robotics and Biocybernetics)
Jozef Stefan Institute, Ljubljana. (Department of Robotics and Biocybernetics)
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Environmental Physiology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Swedish Aerospace Physiology Centre, SAPC. (Avdelningen för Omgivningsfyiologi, Centrum för Flyg- och Rymdfysiologi)
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2019 (English)In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 104, p. 1250-1261Article in journal (Refereed) Published
Abstract [en]

What is the central question of this study? Controlled-hyperthermia heat acclimation protocols induce an array of thermoregulatory and cardiovascular adaptations that facilitate exercise in hot conditions. We investigated whether this ergogenic potential can be transferred to thermoneutral normoxic or hypoxic exercising conditions. What is the main finding and its importance? We show that heat acclimation did not affect maximal cardiac output or maximal aerobic power in thermoneutral normoxic/hypoxic conditions. Heat acclimation augmented the sweating response in thermoneutral normoxic conditions. The cross-adaptation theory according to which heat acclimation could facilitate hypoxic exercise capacity is not supported by our data. ABSTRACT: Heat acclimation (HA) mitigates heat-induced decrements in maximal aerobic power (V̇O2peak ) and augments exercise thermoregulatory responses in the heat. Whether this beneficial effect of HA is observed in hypoxic or thermoneutral conditions remains unresolved. We explored the effects of HA on exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot conditions. Twelve males (V̇O2peak 54.7(5.7) mL·kg-1 ·min-1 ) participated in a HA protocol comprising 10 daily 90-min controlled-hyperthermia (target rectal temperature, Tre  = 38.5 °C) exercise sessions. Before and after HA, we determined V̇O2peak in thermoneutral normoxic (NOR), thermoneutral hypoxic (13.5% Fi O2 ; HYP) and hot (35 °C, 50% RH; HE) conditions in a randomized and counterbalanced order. Preceding each maximal cycling test, a 30-min steady-state exercise at 40% of the NOR peak power output (Wpeak ) was employed to evaluate thermoregulatory responses. HA induced the expected adaptations in HE: reduced Tre and submaximal heart rate (HR), enhanced sweating response and expanded plasma volume. However, HA did not affect V̇O2peak or maximal cardiac output (COmax ) (P = 0.61). Wpeak was increased post-HA in NOR (P < 0.001) and HE (P < 0.001) by 41 ± 21 and 26 ± 22 W, respectively but not in HYP (P = 0.14). Gross mechanical efficiency was higher (P = 0.004) whereas resting Tre and sweating thresholds were lower (P < 0.01) post-HA across environments. Nevertheless, the gain of the sweating response decreased (P = 0.05) in HYP. In conclusion, our data do not support a beneficial cross-over effect of HA on V̇O2peak in normoxic or hypoxic conditions. This article is protected by copyright.

Place, publisher, year, edition, pages
2019. Vol. 104, p. 1250-1261
Keywords [en]
Heat training, cardiac output, cross-adaptation
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:kth:diva-240337DOI: 10.1113/EP087268ISI: 000459938200007PubMedID: 30536521Scopus ID: 2-s2.0-85060572881OAI: oai:DiVA.org:kth-240337DiVA, id: diva2:1271591
Note

QC 20190128

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-08-20Bibliographically approved

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Eiken, Ola

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