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European Journal of Applied Physiology

, Volume 119, Issue 11–12, pp 2513–2527 | Cite as

No ergogenic effects of a 10-day combined heat and hypoxic acclimation on aerobic performance in normoxic thermoneutral or hot conditions

  • Alexandros Sotiridis
  • Panagiotis Miliotis
  • Urša Ciuha
  • Maria Koskolou
  • Igor B. MekjavicEmail author
Original Article

Abstract

Purpose

Hypoxic acclimation enhances convective oxygen delivery to the muscles. Heat acclimation-elicited thermoregulatory benefits have been suggested not to be negated by adding daily exposure to hypoxia. Whether concomitant acclimation to both heat and hypoxia offers a synergistic enhancement of aerobic performance in thermoneutral or hot conditions remains unresolved.

Methods

Eight young males (\(\dot{V}{\text{O}}_{2\max }\): 51.6 ± 4.6 mL min−1 kg−1) underwent a 10-day normobaric hypoxic confinement (FiO2 = 0.14) interspersed with daily 90-min normoxic controlled hyperthermia (target rectal temperature: 38.5 °C) exercise sessions. Prior to, and following the confinement, the participants conducted a 30-min steady-state exercise followed by incremental exercise to exhaustion on a cycle ergometer in thermoneutral normoxic (NOR), thermoneutral hypoxic (FiO2 = 0.14; HYP) and hot (35 °C, 50% relative humidity; HE) conditions in a randomized and counterbalanced order. The steady-state exercise was performed at 40% NOR peak power output (Wpeak) to evaluate thermoregulatory function. Blood samples were obtained from an antecubital vein before, on days 1 and 10, and the first day post-acclimation.

Results

\(\dot{V}{\text{O}}_{2\max }\) and ventilatory thresholds were not modified in any environment following acclimation. Wpeak increased by 6.3 ± 3.4% in NOR and 4.0 ± 4.9% in HE, respectively. The magnitude and gain of the forehead sweating response were augmented in HE post-acclimation. EPO increased from baseline (17.8 ± 7.0 mIU mL−1) by 10.7 ± 8.8 mIU mL−1 on day 1 but returned to baseline levels by day 10 (15.7 ± 5.9 mIU mL−1).

Discussion

A 10-day combined heat and hypoxic acclimation conferred only minor benefits in aerobic performance and thermoregulation in thermoneutral or hot conditions. Thus, adoption of such a protocol does not seem warranted.

Keywords

Heat acclimation Hypoxic acclimation Thermoregulation Aerobic performance 

Abbreviations

ANOVA

Analysis of variance

CO

Cardiac output

ELISA

Enzyme-linked immunosorbent assay

EPO

Erythropoietin

FiO2

Fraction of inspired oxygen

GME

Gross mechanical efficiency

HE

Heat

HR

Heart rate

HSP

Heat shock protein

HYP

Hypoxia

NOR

Normoxia

PiO2

Partial pressure of inspired oxygen

PV

Plasma volume

RH

Relative humidity

RPE

Rating of perceived exertion

SpO2

Capillary oxyhaemoglobin saturation

SV

Stroke volume

Ta

Ambient temperature

Tc

Core temperature

Tre

Rectal temperature

Tsk

Weighted mean skin temperature

\(\dot{V}{\text{O}}_{2}\)

Submaximal oxygen uptake

\(\dot{V}{\text{O}}_{2\max }\)

Maximal aerobic power

VT

Ventilatory threshold

Wpeak

Peak power output

ΔΤf–f

Forearm–fingertip skin temperature difference

Notes

Acknowledgements

We are indebted to Caomhan Conaghan for his enthusiastic assistance during the study and the participants for their commitment.

Author contributions

AS, PM, MK and IBM conceived and designed the research. AS, PM, UC, MK and IBM performed experiments. AS and UC analysed the data. AS interpreted results. AS drafted the manuscript. AS, PM, UC, MK and IBM edited/revised the manuscript critically for important intellectual content.

Funding

Alexandros Sotiridis was recipient of a Young Investigator Postgraduate Fellowship from the Slovene Ministry of Education, Science and Sport (PR-07601).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the national research committee (National Committee for Medical Ethics, Ministry of Health, Republic of Slovenia, no. 0120-494/2018/9) and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Automation, Biocybernetics and RoboticsJozef Stefan InstituteLjubljanaSlovenia
  2. 2.Jozef Stefan International Postgraduate SchoolLjubljanaSlovenia
  3. 3.Section of Sport Medicine and Biology of Exercise, School of Physical Education and Sport ScienceNational and Kapodistrian University of AthensAthensGreece

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