Heat Acclimation with or without Normobaric Hypoxia Exposure Leads to Similar Improvements in Endurance Performance in the Heat

Erik D Hanson; Matthew B Cooke; Mitchell J Anderson; Tracey Gerber; Jessica A Danaher; Christos G Stathis

doi:10.3390/sports10050069

Heat Acclimation with or without Normobaric Hypoxia Exposure Leads to Similar Improvements in Endurance Performance in the Heat

Sports (Basel). 2022 Apr 30;10(5):69. doi: 10.3390/sports10050069.

Authors

Erik D Hanson^{1

2}, Matthew B Cooke³, Mitchell J Anderson⁴, Tracey Gerber⁵, Jessica A Danaher^{5

6}, Christos G Stathis^{2

6}

Affiliations

¹ Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
² Institute for Health and Sport, Victoria University, Melbourne, VIC 8001, Australia.
³ Department of Health Sciences and Biostatistics, Swinburne University, Melbourne, VIC 8001, Australia.
⁴ Metabolic and Vascular Physiology, Baker IDI Heart and Diabetes Institute, Melbourne, VIC 3004, Australia.
⁵ College of Health and Biomedicine, Victoria University, Melbourne, VIC 8001, Australia.
⁶ School of Science, STEM College, Royal Melbourne Institute of Technology (RMIT), Melbourne, VIC 3001, Australia.

Abstract

Background: Combining the key adaptation of plasma volume (PV) expansion with synergistic physiological effects of other acclimation interventions to maximise endurance performance in the heat has potential. The current study investigated the effects of heat acclimation alone (H), combined with normobaric hypoxia exposure (H+NH), on endurance athletic performance.

Methods: Well-trained participants completed a heat-stress trial (30 °C, 80% relative humidity (RH), 20.8% fraction of inspired oxygen (FiO₂)) of a 75 min steady-state cycling (fixed workload) and a subsequent 15 min cycling time trial for distance before and after intervention. Participants completed 12 consecutive indoor training days with either heat acclimation (H; 60 min·day^-1, 30 °C, 80% RH; 20.8% FiO₂) or heat acclimation and overnight hypoxic environment (H+NH; ~12 h, 60% RH; 16% FiO₂ simulating altitude of ~2500 m). Control (CON) group trained outdoors with average maximum daily temperature of 16.5 °C and 60% RH.

Results: Both H and H+NH significantly improved time trial cycling distance by ~5.5% compared to CON, with no difference between environmental exposures. PV increased (+3.8%) and decreased (-4.1%) following H and H+NH, respectively, whereas haemoglobin concentration decreased (-2%) and increased (+3%) in H and H+NH, respectively.

Conclusion: Our results show that despite contrasting physiological adaptations to different environmental acclimation protocols, heat acclimation with or without hypoxic exposure demonstrated similar improvements in short-duration exercise performance in a hot environment.

Keywords: altitude training; concurrent training; heat acclimation; hypoxia; plasma volume.

Grants and funding

This research was funded by Nestle Australia and an internal grant from Victoria University.