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