Effect of 8 days of exercise-heat acclimation on aerobic exercise performance of men in hypobaric hypoxia

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 319; no. 1; pp. R114 - R122
• Main Authors: Salgado, Roy M, Coffman, Kirsten E, Bradbury, Karleigh E, Mitchell, Katherine M, Yurkevicius, Beau R, Luippold, Adam J, Mayer, Thomas A, Charkoudian, Nisha, Alba, Billie K, Fulco, Charles S, Kenefick, Robert W
• Format: Journal Article
• Language: English
• Published: United States 01.07.2020
• Subjects: altitude; exercise performance; acute mountain sickness; self-paced time-trial; Cross-acclimation
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00048.2020

Exercise-heat acclimation (EHA) induces adaptations that improves tolerance to heat exposure. Whether adaptations from EHA can also alter responses to hypobaric hypoxia (HH) conditions remains unclear. This study assessed whether EHA can alter time-trial performance and/or incidence of acute mountain sickness (AMS) during HH exposure. Thirteen sea level (SL) resident men (SL VO peak: 3.19 ± 0.43 l·min ) completed steady-state exercise followed by a 15-min cycle time-trial and assessment of AMS before (HH1; 3,500 m) and after (HH2) an 8-day EHA protocol (120 min; 5 km·hr ; 2% incline; 40°C and 40% RH). EHA induced lower heart rate (HR) and core temperature, and plasma volume expansion. Time-trial performance was not different between HH1 and HH2 after 2-hr(106.3±23.8 vs 101.4±23.0 kJ, p =0.71) or 24-hrs (107.3±23.4 vs 106.3±20.8 kJ, p>0.9). From HH1 to HH2, HR and oxygen saturation at the end of steady-state exercise and time-trial tests at 2 and 24-hrs was not different (p>0.05). Three of 13 volunteers developed AMS during HH1 but not during HH2, while a fourth volunteer only developed AMS during HH2. Heat shock protein 70 was not different from HH1 to HH2 at SL (1.9±0.7 vs 1.8±0.6 NII, p=0.97) or after 23-hrs (1.8±0.4 vs 1.7±0.5 NII, p=0.78) at HH. Our results indicate that this EHA protocol had little to no effect - neither beneficial nor detrimental - on exercise performance in HH. EHA may reduce AMS in those who initially developed AMS, however, studies at higher elevations having higher incidence rates are needed to confirm our findings.