Research investigating thermoregulatory energy costs in free-living humans is limited. We determined the total energy expenditure (TEE) of Tuvan pastoralists living in an extreme cold environment and explored the contribution of physical activity and cold-induced thermogenesis. Twelve semi-nomadic pastoralists (47 ± 8 years, 64 ± 8 kg) living under traditional circumstances, in Tuva, south-central Siberia, Russia, were observed during two consecutive 6-day periods in winter. TEE was measured via the doubly labelled water technique. Skin and ambient temperatures, and physical activity were continuously monitored. The outdoor temperature during the observation period was − 27.4 ± 5.4 °C. During the daytime, the participants were exposed to ambient temperatures below 0 °C for 297 ± 131 min/day. The Tuvan pastoralists were more physically active compared to western populations (609 ± 90 min/day of light, moderate, and vigorous physical activity). In addition, TEE was 13.49 ± 1.33 MJ/day (3224 ± 318 kcal/day), which was significantly larger by 17% and 31% than predicted by body mass, and fat-free mass, respectively. Our research suggests the daily cold exposure combined with high levels of physical activity contributed to the elevated TEE. Future research should reconsider the assumption that energy costs due to thermoregulation are negligible in free-living humans.
Muscle glycogen use and glucose uptake during cold exposure increases with shivering intensity. We hypothesized that cold exposure, with shivering, would subsequently increase glucose tolerance. Fifteen healthy men (age 26 ± 5 years, body mass index 23.9 ± 2.5 kg m-2) completed two experimental trials after an overnight fast. Cold exposure (10°C) was applied during the first trial, via a water-perfused suit, to induce at least 1 h of shivering in each participant. For comparison, a thermoneutral (32°C) condition was applied during the second trial, under identical conditions, for the same duration as determined during the cold exposure. After the thermal exposures, participants rested under a duvet for 90 min which was followed by a 3 h oral glucose tolerance test. Skin temperature (mean ± SE) decreased at the end of the cold exposure compared to before (26.9 ± 0.3 versus 33.7 ± 0.1°C, P < 0.001). Total energy expenditure during the 1 h of shivering was larger than during the time-matched thermoneutral condition (619 ± 23 versus 309 ± 7 kJ, P < 0.001). Cold exposure increased the areas under the glucose and insulin curves by 4.8% (P = 0.066) and 24% (P = 0.112), respectively. The Matsuda and insulin-glucose indices changed after cold exposure by −21% (P = 0.125), and 30% (P = 0.100), respectively. Cold exposure did not subsequently increase glucose tolerance. Instead, the Matsuda and insulin-glucose indices suggest insulin resistance post-shivering.
Muscle glycogen use and glucose uptake during cold exposure increases with shivering intensity. We hypothesized that cold exposure, with shivering, would subsequently increase glucose tolerance. Fifteen healthy men (age = 26 ± 5 yr, body mass index = 23.9 ± 2.5 kg m -2 ) completed two experimental trials after an overnight fast. Cold exposure (10°C) was applied during the first trial, via a waterperfused suit, to induce at least 1 h of shivering in each participant. For comparison, a thermoneutral (32°C) condition was applied during the second trial, under identical conditions, for the same duration as determined during the cold exposure. After the thermal exposures, participants rested under a duvet for 90 min which was followed by a 3-h oral glucose tolerance test. Skin temperature (mean ± SE) decreased at the end of the cold exposure compared to before (26.9 ± 0.3 vs. 33.7 ± 0.1°C, P < 0.001). Total energy expenditure during the 1 h of shivering was larger than during the timematched thermoneutral condition (619 ± 23 vs. 309 ± 7 kJ, P < 0.001). Cold exposure increased the areas under the glucose and insulin curves by 4.8% (P = 0.066) and 24% (P = 0.112), respectively. The Matsuda and insulin-glucose indices changed after cold exposure by −21% (P = 0.125), and 30% (P = 0.100), respectively. Cold exposure did not subsequently increase glucose tolerance. Instead, the Matsuda and insulin-glucose indices suggest insulin resistance post-shivering.
ObjectivesThis study compared the metabolic and vascular responses, to whole‐body and finger cold exposure, of a traditional population lifelong exposed to extreme cold winters with Western Europeans.MethodsThirteen cold acclimatized Tuvan pastoralist adults (45 ± 9 years; 24.1 ± 3.2 kg/m2) and 13 matched Western European controls (43 ± 15 years; 22.6 ± 1.4 kg/m2) completed a whole‐body cold (10°C) air exposure test and a cold‐induced vasodilation (CIVD) test, which involved the immersion of the middle finger into ice‐water for 30 min.ResultsDuring the whole‐body cold exposure, the durations until the onset of shivering for three monitored skeletal muscles were similar for both groups. Cold exposure increased the Tuvans' energy expenditure by (mean ± SD) 0.9 ± 0.7 kJ min−1 and the Europeans' by 1.3 ± 1.54 kJ min−1; these changes were not significantly different. The forearm‐fingertip skin temperature gradient of the Tuvans was lower, indicating less vasoconstriction, than the Europeans during the cold exposure (0 ± 4.5°C vs. 8.8 ± 2.7°C). A CIVD response occurred in 92% of the Tuvans and 36% of the Europeans. In line, finger temperature during the CIVD test was higher in the Tuvans than the Europeans (13.4 ± 3.4°C vs. 3.9 ± 2.3°C).ConclusionCold‐induced thermogenesis and the onset of shivering were similar in both populations. However, vasoconstriction at the extremities was reduced in the Tuvans compared to the Europeans. The enhanced blood flow to the extremities could be beneficial for living in an extreme cold environment by improving dexterity, comfort, and reducing the risk of cold‐injuries.
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