The combined effect of hypoxia and cold on substrate metabolism in men at rest

Crant, Robert A. (2020) The combined effect of hypoxia and cold on substrate metabolism in men at rest. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (956kB)

Abstract

This study was designed to examine the acute metabolic response of men to the combined exposure to cold and hypoxia at rest. As the individual effects of both conditions have been extensively studied, our research focused on their combined effects in an effort to develop a better understanding of a lesser known topic. Eight participants (age:28.9±11.8 y; weight:80.7±11.5 kg; height:175.8±0.067 m; BMI:29±11 kg∙m⁻²) were recruited to participate in three experimental sessions for two hours on separate days. The experiment conditions included cold (C), hypoxia (H), and both cold and hypoxia combined (CH). Participants were asked to fast for 12 hours prior to beginning each experimental session. Once they arrived at the laboratory, the participants were instructed to lay in a supine position on a bed and were placed underneath a canopy for 30 minutes to measure their basal metabolic rate (BMR). Once the BMR protocol was complete, participants were then fitted with 4 wireless Electromyography (EMG) electrodes [trapezius (TR), pectoralis major (PE), rectus abdominis (RA), and rectus femoris (RF)] and were instructed to complete a maximal voluntary contraction (MVC) protocol for all four muscles. Shivering activity throughout the experimental sessions was expressed as percentage of the MVC values for each muscle group. Upon the completion of the MVC protocol, participants were asked to self-insert a rectal thermocouple, used to monitor core-body temperature throughout the sessions. Next, 11 skin thermo-sensors, using a modified Hardy and Dubois 12-point system, were applied directly to their skin, before they were finally fitted with a liquid conditioned suit. Once all initial procedures were complete, they were then transferred to an enclosed chamber to be exposed, in a random order while in a seated position, to C (FIO2=0.2093, 10°C), H (FᵢO₂=0.135 or ~2500m), or CH (10°C + FᵢO₂=0.135). Mean skin temperature significantly dropped over time during exposure in the climatic chamber from 31.9±0.9°C to 26.9±0.9°C and from 32.6±0.8°C to 26.4±1.0°C for C and C+H respectively, with no change in H, from 32.5±0.7°C to 33.1±0.7°C. Energy production (EP) responded accordingly, as it significantly increased over time from 5.8±0.6kcal·min⁻¹ to 10.6±1.9 kcal·min⁻¹ and from 6.0±0.9 kcal·min⁻¹ to 10.6±1.4 kcal·min⁻¹ for C and CH, respectively. A slight non-significant effect was observed in H, from 5.8±0.4 kcal·min⁻¹ to 6.7±0.7 kcal·min⁻¹. This effect was attributed to the seated position of the participants during exposure. The individual contributions of substrates to EP significantly differed between conditions over time, as glucose oxidation was higher during C when compared to H and CH, while lipid oxidation was higher during CH compared to C and H. To conclude, while the combination of CH did not impact energy production when compared to the other conditions, it did alter the contribution of individual substrates to energy production.

Actions (login required)

View Item