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Thermoregulation
Normal body temperature fluctuates several degrees during the day in response to physical activity, emotions, and ambient temperature variations.Body temperature exhibits diurnal fluctuations: Lowest temperatures occur during sleep. Slightly higher temperatures persist awake. TERM 2
Contributing factors to heat gain and loss to
regulate core temperature at
DEFINITION 2 98.6F (37C). TERM 3
Thermal Balance Equation
DEFINITION 3 +M-E+/-TR+/-CD+/CV+SRWhere:M = MetabolismE = EvaporationTR = Thermal RadiationCD = ConductionCV = ConvectionSR = Solar Radiation TERM 4
Core Temperature During Physical Activity
DEFINITION 4 Heat generated by active muscles increase core temp to fever levels that incapacitate a person if caused by external heat stress alone. Increased core temp with PA does not reflect heat dissipation failure. Modest core temperature increase reflects favorable internal adjustments that create optimal thermal conditions for physiologic and metabolic function TERM 5
Intense PA for 2 to 3 hrs can induce
dehydration
DEFINITION 5 Can impede heat dissipation and compromise CV function and performanceAverage water loss per hour from sweating at various air temp during rest and light and moderate PA
Fluid Loss in Physical Activity
For acclimatized person, sweat loss peaks at 3 Lh1 during intense PA in heat and averages nearly 12 L/d. Intense sweating for several hr induces sweat gland fatigue that impairs core temp regulation. Hot, humid environ impede effectiveness of evaporative cooling and promotes large fluid losses TERM 7
Consequences of Dehydration
DEFINITION 7 Any dehydration impairs physiologic function and thermoregulation.Plasma volume decreases as dehydration progresses: Peripheral blood flow and sweating rate decrease to make thermoregulation more difficult. Premature fatigue occurs from reduced plasma volume that increases HR, RPE, core temp. Loss of plasma volume produces two effects: Initiates increases in systemic vascular resistance Reduces skin blood flow TERM 8
Factors That Affect Sweat-Loss Dehydration
DEFINITION 8 PA intensityPA durationEnvironmental tempSolar loadWind speedRelative humidityClothingWater Requirements (LH1) for rest and varying intensities of PA in the heat; indoors and outdoors at diverse temperatures and RH. TERM 9
Water Replacement and Rehydration
DEFINITION 9 Adequate fluid replacement sustains evaporative cooling of acclimatized humans. Proper scheduling of fluid replacement maintains plasma volume for optimal circulation and sweating progress. Well-hydrated athletes always function at a higher physiologic and performance level than dehydrated athletes. TERM 10
Acclimatization
DEFINITION 10 Repeated heat exposure with PA improves capacity for PA with less discomfort; optimal acclimatization requires adequate hydration.
Existing Age-Related Thermoregulatory
Differences: Children
Prepubescent children show lower sweating rate and higher core temperature during heat stress.Children take longer to heat acclimatize.Children exposed to environmental heat stress should exercise at a reduced intensity and receive additional time to acclimatize. TERM 17
Gender and Thermoregulation
DEFINITION 17 Women and men equally tolerate physiologic and thermal stress of PA when matched for fitness and acclimatization levels. Gender differences occur for four thermoregulatory mechanisms: Sweating Evaporative versus circulatory cooling Body surface area-to-mass ratio Menstruation TERM 18
Excess body fat
DEFINITION 18 Excess body fat negatively impacts performance in hot environments. Fats specific heat exceeds that of muscle tissue to insulate the bodys shell to retard peripheral heat conduction. Large overfat persons possess a smaller body surface area-to- mass ratio for sweat evaporation compared with leaner, smaller persons. Excess body fat directly adds to energy expended in weight- bearing activities. TERM 19
Cold Weather Physical Activity
DEFINITION 19 Human exposure to extreme cold produces considerable physiologic and psychologic challenges.Cold ranks high among the differing terrestrial environmental stressors for its potentially lethal consequences. Body loses heat 2 to 4 faster in cool water compared with air at the same temperature. Metabolic heat generated by muscular activity contributes to thermoregulation during cold stress. Individual differences in body fat content significantly effects physiologic function in a cold environment during rest and PA. TERM 20
Five factors compromise core temperature
regulation in the cold
DEFINITION 20 Chronic exertional fatigue Sleep loss Inadequate nourishment Reduced tissue insulation Depressed shivering heat production
Acclimatization to Cold
Humans adapt more poorly to chronic cold exposure than heat exposure. Increased heat production does not accompany body heat loss; individuals regulate at a lower core temperature in the cold. Repeated cold exposure of hands or feet brings about blood flow increases through these anatomic regions during cold stress. TERM 22
Early warning signs of cold injury include:
DEFINITION 22 Tingling and numbness in fingers and toes Burning sensation in nose and ears Disregarding signs of overexposure leads to frostbite
