Decrease in Body Temperature: Effects on Motor Nervous System Function, Exercise Performance and Response to Active Heating

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Hurrie, Daryl M.G.
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Introduction: Canadians are exposed to cold environments much of the year. Cold affects participants in athletic, recreational, commercial and military activities. Cold exposure may change peripheral and/or central temperature, and this may have positive or negative consequences on human physiology and performance. Applied health sciences (AHS) practitioners should understand the wide-ranging consequences that cold exposure has on performance and recovery, and methods for reversing maladies caused by excessive cold exposure (e.g., hypothermia). Methods: Study one: corticospinal and spinal excitability were assessed via transcranial magnetic stimulation (motor cortex) and electrical stimulation (cervicomedullary junction) following skin cooling and rewarming. Results reveal the effects cooling has on areas of signal transmission involved in voluntary movement. Study two: three 30-min recovery strategies were performed between two identical sets of 3x30-s Wingate tests. Recovery periods included; leg cycling in cold or thermoneutral water, or sitting passively in thermoneutral water. Study three: shivering was pharmacologically inhibited in hypothermic participants following cold water immersion. The efficacy of three rewarming strategies were studied: electric heat pad, forced air warming blanket, and spontaneous rewarming. Results: In cold participants spinal excitability is facilitated by reduced skin or core temperature, while corticospinal excitability remains unchanged. Increases in spinal excitability may contribute to shivering, and may compensate for unchanging, or even decreasing corticospinal excitability. Active recovery in cold water successfully decreased core temperature and blood lactate, and likely maintained muscle temperature above baseline values. However, small significant post-recovery decreases in peak and average power occurred. Finally, in 2 hypothermic, non-shivering participants, there were no differences between either active warming methods or spontaneous warming for post cooling afterdrop or core rewarming rate. Conclusions: These studies inform practitioners on: 1) the effects of general cooling on neural pathways associated with voluntary movement, 2) the efficacy of active recovery during cold or thermoneutral water immersion on sprint interval training, and 3) the efficacy of rewarming hypothermic individuals with a novel field-based heating device. Results provide insight into physiological responses to cold exposure which are relevant to AHS practitioners in a variety of settings.
Thermoregulation, Environmental Medicine, Exercise Physiology, Shivering, Hypothermia
Hurrie, D. M. G., & Giesbrecht, G. G. (2020). Is active recovery during cold water immersiion bettern than active or passive recovery in thermoneutral water for post-recovery high intensity exercises performance? Appl Physiol Nutr Metab, 45(3), 3. doi:10.1139/apnm-2019-0189
Hurrie, D. M. G., Hildebrand, E., Arnould, S. M., Plett, J., Bellan, D., Buchel, A., & Giesbrecht, G. G. (2020). Comparison of Electric Resistive Heating Pads and Forced-Air Warming for Pre-hospital Warming of Non-shivering Hypothermic Subjects. Mil Med, 185(1-2), e154-e161. doi:10.1093/milmed/usz164