Shivering in the cold: from mechanisms of fuel selection to survival

Abstract

Haman, François. Shivering in the cold: from mechanisms of fuel selection to survival. J Appl Physiol 100: 1702-1708, 2006; doi:10.1152/japplphysiol.01088.2005.-In coldexposed adult humans, significant or lethal decreases in body temperature are delayed by reducing heat loss via peripheral vasoconstriction and by increasing rates of heat production via shivering thermogenesis. This brief review focuses on the mechanisms of fuel selection responsible for sustaining long-term shivering thermogenesis. It provides evidence to explain large discrepancies in fuel selection measurements among shivering studies, and it proposes links between choices in fuel selection mechanism and human survival in the cold. Over the last decades, a number of studies have quantified the contributions of carbohydrate (CHO) and lipid to total heat generation. However, the exact contributions of these fuels still remain unclear because of large differences in fuel selection measurements even at the same metabolic rate. Recent advances on the mechanisms of fuel selection during shivering provide some plausible explanations for these discrepancies between shivering studies. This new evidence indicates that muscles can sustain shivering over several hours using a variety of fuel mixtures achieved by modifying diet (changing the size of CHO reserves) or by changing muscle fiber recruitment (increasing or decreasing the recruitment of type II fibers). From a practical perspective, how does the choice of fuel selection mechanism affect human survival in the cold? Based on a glycogen-depletion model, estimates of shivering endurance show that, whereas the oxidation of widely different fuel mixtures does not improve survival time, the selective recruitment of fuel-specific muscle fibers provides a substantial advantage for cold survival. By combining fundamental research on fuel metabolism and applied strategies to improve shivering endurance, future research in this area promises to yield important new information on what limits human survival in the cold. energy metabolism; shivering thermogenesis; fuel selection; survival in the cold; thermoregulation SURVIVAL IN COLD ENVIRONMENTS has been an ongoing challenge for humans over the ages. As furless endotherms, they are well adapted for dissipating heat in warm climates but particularly bad at retaining it in cold environments. Over the past decades, much emphasis from an engineering standpoint has been placed on the development of protective clothing and shelters to reduce excessive heat loss and allow long-term survival in cold environments. Today, these efforts have improved access to more extreme climates for occupational and recreational activities. However, this greater accessibility has also increased the risks for cold-related injuries and/or hypothermia. In coldexposed adult humans, significant or lethal decreases in body temperature are delayed by reducing rates of heat loss via peripheral vasoconstriction and by increasing rates of heat production (Ḣ prod ) via shivering thermogenesis. ...

Mice lacking G0S2 are lean and cold-tolerant

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“…12, 13, 15 among others), but demonstrating D2 activity convincingly has been a challenge, except in the newborn mouse (5), to the point that some researchers estimate it unlikely that D2 plays a significant role as a local or systemic source of T 3 (13) in this species. However, skeletal muscle has been long known as a thyroid hormone-responsive tissue (45), and it participates in shivering (46), as well as in nonshivering, thermogenesis (47). This latter function is thought to result largely from stimulation by T 3 of Ca 2ϩ turnover via stimulation of SERCA activity and an enlarged sarcoplasmic Ca pool.…”

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