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Training, The Environment, & Ergonomic Aids. Chapter 15 Applied Exercise Physiology. Thermoregulation. Basics Cold Stress Heat Stress Heat Dissipating Mechanisms Clothing Exercise in Heat Sweating Heat Tolerance Cold Tolerance. . Basics-1. Body temp fluctuates throughout the day
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Training, The Environment, & Ergonomic Aids Chapter 15 Applied Exercise Physiology
Thermoregulation • Basics • Cold Stress • Heat Stress • Heat Dissipating Mechanisms • Clothing • Exercise in Heat • Sweating • Heat Tolerance • Cold Tolerance
Basics-1 • Body temp fluctuates throughout the day • Lower in sleep; higher when awake- even during “lazing” • Tcore = Core Temperature • Eardrum, rectum, esophagus • Estimate the temperature of the hypothalamus • Oral Temperature is 1F less than rectal temperature • The body can tolerate a core temperature can drop 18F, but only increase 5F.
Basics-2 • Tskin = Shell Temperature • Arm, trunk, leg, head, etc. • Tbody = Mean Body Temperature (est. of avg. core temp • Tbody = (0.6 x Tcore)+ (0.4 x Tskin) • Hypothalamus= central coordinating center for temperature regulation; cannot “shut off” the heat • Thermal Receptors • Temperature changes in the blood
Cold Stress • When at rest in extreme cold: • Reduce heat loss • Increase heat production • Physiological Adaptations • Vascular Constriction • Muscular Activity • Hormonal Output (epinephrine & norepinephrine increase heat production; prolonged exposure releases thyroxine to elevate resting metabolism)
Heat Stress • Without thermoregulation, CBT could increase 1.8F per minute in intense, sustained exercise (3min=bad) • Mechanisms • Radiation • Conduction • Convection • Evaporation
Heat Dissipating Mechanisms • Circulatory System- Workhorse • Blood to skin for convection, conduction, radiation, & evaporation • Sweating begins seconds after vigorous exercise; after 30 min an equilibrium is established • Hormonal adjustments to conserve salts (aldosterone) & fluid lost in sweating (ADH; vasopressin)
Clothing • Cold- • Several layers or layers with fur, feathers, or synthetic fabrics • Wet clothing loses 90% of insulating qualities; heat moves away from the body faster since H2O conducts heat faster than air • Heat- • Loose fitting or moisture wicking fabrics • Light colors to help evaporate sweat & reflect heat
Exercise in Heat • Circulatory system competes: • Increase BF to active muscles • Increase BF to skin to dissipate heat • Sweating reduces blood plasma volume which decreases SV and increases HR • Max cardiac output & aerobic capacity decreases in heat exercise since increased HR isn’t offset by decreased SV • Core temp should increase in exercise; shows optimal physical functioning
Sweating • Blood plasma supplies most of sweat • Diuretics & laxatives or vomiting = dehydration • If left on their own, athletes only replace ½ of H2O lost during exercise • Dehydration • Increases systemic resistance to maintain BP • Decreases BF to skin which decreases heat dissipation • Dehydration in cold weather • Cold air has less moisture • Fluids used to humidify & warm incoming air • Cold increases urine production • Overdressing = more sweating
Heat Tolerance • Heat acclimatization- physiologic changes that increase heat tolerance • First sessions in heat should be light intensity & only 15-20 minutes • Benefits dissipate after 2-3 weeks in regular temperatures • Exercise in actual heat increases acclimatization and is more beneficial than simulated heat exercise • Excess body fat makes it harder to regulate temperature in heat because: • Fat is warmer than muscle • Fat insulates/holds more heat; prevents dissipation • Smaller body surface area to mass ratio= decreased evaporation • Heat Stress Index p. 535
Cold Tolerance • Wind Chill Index p. 536 • Cold air does not damage respiratory tract
Altitude • Barometric pressure decreases @ higher • Po2= density of O2 molecules • Dry, ambient air contains 20.9% oxygen • Does this change at different altitudes?
