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ThermoregulationChapter 10
Transfer of Body Heat◦ Conduction ◦ Convection◦ Radiation◦ Evaporation
Humidity and Heat Loss
Mechanisms of Body Temperature Regulation
Mechanisms of Body Temperature Regulation
Effect of air temperature on effectiveness of avenues of heat loss
Mechanisms of Body Temperature Regulation
Efficiency of Energy Systems and Temperature
Hypothalamus Body Temperature and Effectors
◦ Sweat glands◦ Smooth muscle around arterioles◦ Skeletal muscle◦ Endocrine glands
Mechanisms of Body Temperature Regulation
CV Responses Energy Production
◦ Glycogen dependence and lactate Driven by epinephrine
Body Fluid Balance – Sweating◦ Heavy and light sweating – electrolytes◦ Blood volume changes – aldosterone and ADH
secretion
Physiological Responses to Exercise in the Heat
Heat Stress◦ Air temperature, humidity, air velocity, & amount
of thermal radiation all influence heat stress◦ Wet bulb globe temperature (WBGT) – designed to
account for all avenues of heat loss and gain. Difference between WB and dry bulb is an indicator
of environments ability to cool by evaporation Black globe temperature is an indicator of
environments capacity for transmitting radiated heat.
◦ Overall challenge to body temperature is expressed as WBGT WBGT = 0.1 TDB + 0.7 TWB + 0.2 TG
Exercise in the Heat
Heat Related Disorders◦ Heat Cramps
Ss - severe cramping of primary muscles due to mineral losses and dehydration
Tx – move to cooler location and administer fluids or saline solution
◦ Heat Exhaustion Ss – extreme fatigue, dizziness, dyspnea, nausea, cold
or clammy or hot and dry skin, weak, rapid pulse. CV unable to meet body’s needs Tx – move to cooler environment with elevated feet,
salt water administered, IV saline if unconcious. If untreated can result in heat stroke
Exercise in the Heat
◦ Heat Stroke Ss – core temperature >40⁰C (104 ⁰ F, cessation of
sweating, hot and dry skin, rapid pulse and respiration, hypertension, confusion or unconciousness
Untreated can progress to coma and death Tx – rapid cooling in a cold bath or wrapping in wet
sheets and fanning the victim Cause is failure of thermoregulatory mechanisms
Exercise in the Heat
Preventing Hyperthermia◦ When possible decrease effort to decrease heat
production◦ Recognize Ss of hyperthermia◦ When WBGT exceeds 28 ⁰C (82.4 ⁰ F) do not
practice or compete outdoors◦ Frequent fluid breaks◦ Appropriate clothing – skin exposure
Exercise in the Heat
Adjustments of the body to repeated, prolonged exercise bouts in the heat
Result is an increased ability to dissipate heat and reduce risk of heat illness◦ Sweat rate increases◦ Amount of sweat produced in exposed areas
increases◦ Sweating starts earlier – creates heat gradient◦ Less mineral content in sweat
Heat Acclimatization
Body temperature and heart rate increase to a lesser degree during exercise at any heat load
Decrease rate of glycogen utilization after acclimitization
Heat Acclimatization
Achieving heat acclimatization depends on exposure to a hot environment plus ◦ The environmental conditions during each session◦ Duration of heat exposure◦ Intensity of exercise
5-10 days of training in the heat will result in acclimatization.◦ Training intensity should be reduced in first few
days to prevent heat illness
Heat Acclimatization
Exercise in the Cold
Exercise in the Cold Cold Stress – any environmental condition
that causes a loss of body heat that threatens homeostasis
A decrease in skin or blood temperature stimulates mechanisms designed to produce heat and conserve heat
Exercise in the Cold
Mechanisms:◦ Shivering◦ Nonshivering thermogenesis◦ Peripheral vasoconstriction
Factors to consider in heat loss◦ Temperature gradient◦ Surface area◦ Windchill
Exercise in the Cold
Physiological Responses to Exercise in the Cold◦ Muscle function◦ Metabolic responses
Health Risks◦ Hypothermia◦ Cardiorespiratory effects
Exercise in the Cold
Increased subcutaneous fat Greater cold tolerance
◦ Increased blood flow and warming of exposed areas
Acclimatization to the Cold