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Oxygen Consumption and Substrate Oxidation Rates Following Passive Acclimation to a Hot Environment
Author(s) -
Etter Clara Vada,
Beaudin Andrew E.,
Walsh Michael L.,
White Matthew D.
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.08737
Subject(s) - acclimatization , zoology , oxygen , chemistry , vo2 max , medicine , biology , heart rate , ecology , organic chemistry , blood pressure
Acclimation to a hot environment via prolonged or repeated, daily exposure to a heat stress results in adaptations of the human thermoregulatory responses. In this study, it was investigated whether metabolic responses to passive heat acclimation (HA) adapted similarly to thermoregulatory heat loss responses including following a 10‐day, 2 h·day −1 passive heat acclimation (HA) to 50°C and 20 % RH. This study was approved by the Simon Fraser University Office of Research Ethics. Purpose It was hypothesized that, similar to that seen during active heat acclimation with exercise, there would be an elevation of oxygen consumption following a passive heat acclimation. It was also hypothesized that following heat acclimation there would be increased lipid oxidation relative to the pre‐acclimation state. Methods Nine male participants performed two immersions in a 40°C bath separated by a 10‐day passive heat acclimation. Heat acclimation was performed in a climatic chamber controlled at 50°C and 20 % RH where participants remained seated at rest for 2 hr·day −1 with their rectal temperature maintained between 38.5 – 39.0°C. A two‐way repeated measures ANOVA with factors of Acclimation State (Pre and Post) and delta T ES (0 to 1.4°C above rest) was employed with post hoc analysis completed with two‐tailed, paired t‐tests. The significance level was p<0.05. Results HA was confirmed by a significant decrease in resting esophageal temperature (T ES ) from 37.60 ± 0.19 (mean ± SD) to 37.31 ± 0.11°C (p=0.001). During the 40°C immersions significant decreases in the T ES thresholds for temple cutaneous blood velocity from 37.34 ± 0.12 to 37.14 ± 0.16°C (p=0.008) and for forehead eccrine sweating from 37.61 ± 0.21 to 37.24 ± 0.24°C (p=0.007) also confirmed heat acclimation. HA did not influence oxygen consumption from 0.21 ± 0.07 to 0.22 ± 0.07 L/min (p=0.15). Carbohydrate oxidation rate increased from 0.21 ± 0.21 to 0.28 ± 0.26 g·min −1 (p=0.002). Lipid oxidation rate decreased from 1.16 ± 0.22 to 1.09 ± 0.24 g·min −1 (p<0.001). Conclusion Following a passive heat acclimation the evidence reports no change in oxygen consumption, and contrary to that hypothesized, there was a decrease in lipid oxidation rate and an increase in carbohydrate oxidation rate. Support or Funding Information Funding Source This project was supported by Natural Sciences and Engineering Research Council of Canada and the Canada Foundation for Innovation.