Neuromuscular mechanisms for cold-induced changes in voluntary and involuntary muscle activity

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Hundreds of Canadians die annually from cold exposure, often during cold-water immersion. Survival and recovery can be improved by understanding our body's physiological responses to cold. My research program focuses on physiologic mechanisms contributing to enhancing physical performance and survival in the cold. Thus, I intend to further study mechanisms for, and implications of cold-induced reduction in voluntary muscle activity and involuntary shivering. Magnetic stimulation (MS) and electrical stimulation (ES) of muscle activity, will identify effects of local muscle and/or body core cooling on excitatory and inhibitory neural pathways. Transcranial MS (at the top of the skull) stimulates the entire motor pathway from corticospinal neurons, to motor neuron, to muscle. Cervico-medullary ES (at the base of the skull) specifically stimulates spinal motor neurons. We will also specifically explore the effects of cooling the body core and/or the local muscle during brief and fatiguing voluntary muscle contractions. Therefore, we can differentiate between local and central neural circuits and whether they are excitatory or inhibitory, and determine the proportional contribution of each. These techniques will also help determine central mechanisms that account for submaximal shivering intensity, even when core temperature is decreasing (a condition when one would expect a maximal response but it is not). During many of the studies in this research program, we will determine if there is an effect of sex on the responses. Results could direct future research to maximize muscle contraction and shivering during cold-water survival situations. Finally, if there are sex effects, female data may be used to improve cold survival models used by the Canadian Coast Guard. I intend to train 8-10 HQP in the next 5 years, who will become exercise scientists, university professors, physicians and physiotherapists. Some of these HQP will be involved in teaching or coaching on topics that will improve both performance, safe participation and survival in extreme environments.