Environmental Physiology Introduction to Heat and Cold Exercise Outcomes - MEDI 2023 - PDF

Environmental Physiology Introduction to heat and cold exercise outcomes Dr Natalie Kwai Senior Lecturer  What you should be able to do after this Lecture: Recall heat transfer principles and...

Environmental Physiology Introduction to heat and cold exercise outcomes Dr Natalie Kwai Senior Lecturer  What you should be able to do after this Lecture: Recall heat transfer principles and thermoregulation Describe heat transfer parameters of relevance to exercise Learning Describe key alterations in physiological function in response to excessive heat Outcomes Describe extreme heat illness (EHI) and symptoms of EHI Briefly describe key alterations to physiological function in response to cold exposure Resources Périard JD, Eijsvogels TMH, Daanen HAM. Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies. Physiol Rev. 2021 Oct 1;101(4):1873-1979. doi: 10.1152/physrev.00038.2020. Epub 2021 Apr 8. PMID: 33829868. Feng, Z., Hu, Y., Yu, S., Bai, H., Sun, Y., Gao, W., Li, J., Qin, X. and Zhang, X., 2023. Exercise in cold: Friend than foe to cardiovascular health. Life Sciences, p.121923. Tipton M, Bradford C. Moving in extreme environments: open water swimming in cold and warm water. Extrem Physiol Med. 2014 Jun 11;3:12. doi: 10.1186/2046-7648-3-12. PMID: 24921042; PMCID: PMC4052348. Plowman, S.A. and Smith, D.L., 2013. Exercise physiology for health fitness and performance. Lippincott Williams & Wilkins. Paal P, Pasquier M, Darocha T, Lechner R, Kosinski S, Wallner B, Zafren K, Brugger H. Accidental Hypothermia: 2021 Update. International Journal of Environmental Research and Public Health. 2022; 19(1):501. https://doi.org/10.3390/ijerph19010501 Heat Physiology Revision: Control Systems Physiology (MEDI 211) The body holds its temperature within a tightly managed range - Physiological processes (inc. enzyme function, Hb affinity to O2) Failure to maintain body temperature within this range results in adverse outcomes How is it controlled Thermal ThermalBalance Balance Revision: Control Systems Physiology (MEDI 211)  Introduction Heat exchange Periard et al. (2021)  Environmental Parameters Thermal Balance And how they affect heat transfer Four main environmental parameters affect the biophysical properties of human heat balance 1. Ambient temperature During exercise, ambient temperatures higher than skin temperature= dry-heat gain vs lower temperatures = heat loss Environments with a high ambient temperature and low humidity = evaporative heat loss 2. Humidity Higher humidity reduces evaporative heat loss 3. Air velocity Affected by wind speed, direction of travel during exercise and terrain Displacement of air across body = convective heat exchange (dependent on thermal gradient) 4. Solar radiation Periard et al. (2021) Depends on location on earth, time of day season, and level of skin area exposed  thermal gradient = heat transfer Environmental Parameters Thermal Balance And how they affect heat transfer Task dependent parameters which affect the biophysical properties of human heat balance 1. Metabolic Heat production Only 25% of metabolic energy is converted into mechanical work -> rest is lost as heat 2. Clothing Barrier between skin and environment Affect heat exchange - Water vapor evaporation - Exposure to solar radiation (skin coverage and/or reflective garments) Environmental Parameters Thermal Balance And how they affect heat transfer Personal parameters which affect the biophysical properties of human heat balance 3. Body surface area Larger surface area = increased evaporative heat loss 4. Body surface to mass ratio High body surface area-to-mass ratio experience less heat storage during uncompensable heat exposure than those with a lower ratio, due to the larger area for dry and evaporative heat loss relative to body mass E.g. smaller, heavier people do not release heat as well as larger people of the same weight 5. Sex Males have a higher sweat rate but Females have higher density of activated sweat glands during moderate intensity exercise (Bar-Or et al. 1968 and Shapiro et al. 1980) Environmental Parameters Thermal Balance And how they affect heat transfer Personal parameters which affect the biophysical properties of human heat balance 6. Age Older individuals have alterations to thermoregulator capacity and fluid regulation More susceptible to hyperthermia Children have underdeveloped thermoreg and fluid reg in addition to high BSA:M - Note: this may only be relevant in extreme environmental conditions compared to adults 7. Aerobic fitness Aerobic fitness positively correlates with enhanced heat loss capacity Response to training that improve heat transfer - Increased skin blood flow at lower core temp from increased Qc and increased BV - Increased sweat function Thermoregulation Thermal Balance A recap  Heat Exercise Exchange in heat Impact on function of different systems  Heat Exercise Exchange in heat Heat Illness When the cardiovascular system cannot meet the thermoregulatory and metabolic demands of the body, heat illness ensues Exertional Heat Illness occurs via a combination of exertional and heat stress and is most likely encountered by exercise professionals. Defined as a range of multisystem illnesses related to elevated body core temp (hyperthermia) - Physiological disruption of several organs or systems and can vary in severity  Heat Exercise Exchange in heat Heat Illness  Heat Exercise Exchange in heat Heat illness – risk factors  Heat Exercise Exchange in cold A recap on thermoregulation in cold Based on previous slides, what factors might affect alterations to an athlete’s heat transfer in cold?  Heat Exercise Exchange in cold The other end of the spectrum From a metabolic standpoint: Increases oxygen consumption in a dose-dependent manner in both active and passive cold water immersion and on land. - Shivering thermogenesis adds to cost Feng et al. (2023)  Heat Exercise Exchange in cold The other end of the spectrum From a metabolic standpoint: Increases oxygen consumption in a dose-dependent manner in both active and passive cold water immersion and on land. - Shivering thermogenesis adds to cost Nervous system alterations Conduction slowing in nervous system Altered peripheral sensation - Altered sensory feedback Tipton and Bradford (20214)  Heat Exchange Hypothermia What is it Core temp =