Grant: Discovery Grants Program - Individual

Throughout evolution, humans have acquired efficient metabolic and physiological defenses to dissipate heat in warm climates. However, their furless bodies do little to prevent excessive heat loss in cold environments. In the cold, humans must rely on the concerted activation of metabolic and physiological processes that increase heat production and lower heat loss. When exercise is not possible, the increase in heat production is achieved involuntarily by the activation of shivering and to a lesser extent by nonshivering thermogenesis. By combining metabolic, isotopic, biochemical and electrophysiological approaches, the long-term objective of the proposed research program is to better understand the plasticity and interindividual variability of the mechanisms that regulate and maintain thermogenenic processes in humans exposed to adverse environments. Currently, it focuses on three main areas of research: 1) the relationship between muscle mass, thermogenic capacity and the partitioning of metabolic fuels, 2) plasticity and interindividual variability to cold acclimation, 3) the relationship between muscle mass distribution and changes in muscle activity during shivering. These overall questions constitute the continuation of previous experiments conducted for the last 16 y in my laboratory. They will advance the current knowledge by focusing on the plasticity and interindividual variability of cold responses in non-cold acclimatized and cold acclimatized women and men. Building on our previous studies, the proposed work will quantify the importance of: 1) individual variations in body morphology and composition on metabolic responses during acute cold exposure, 2) cold acclimation on changes and interindividual variability in the respective contributions of shivering and nonshivering thermogenesis to heat production, 3) the changes in muscle activity during shivering as they relate to the regional distribution of muscle mass. Building on the knowledge gained in the last fifteen years of NSERC funding, the proposed experiments will include the combination indirect calorimetry, whole body metabolic tracer and electromyographic methodologies developed in the applicant laboratory. This work will aim at better understanding the metabolic requirements of individual tissues in cold exposed adult humans and the metabolic requirements of shivering muscles. These combined techniques will allow the applicant and his trainees to establish more clearly the interindividual factors that modulate the relative use of metabolic fuels and the relative contribution of shivering and nonshivering thermogenesis. Results from this research program, together with the novel experimental approach, will expand on previous work funded by NSERC and provide novel information for shivering research. It will help achieve the long term objective of improving the characterization of the metabolic basis of shivering in humans.