Chapter 10

 Transfer of Body Heat ◦ Conduction ◦ Convection ◦ Radiation ◦ Evaporation  Humidity and Heat Loss

 Efficiency of Energy Systems and Temperature  Hypothalamus  Body Temperature and Effectors ◦ Sweat glands ◦ Smooth muscle around arterioles ◦ Skeletal muscle ◦ Endocrine glands

 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

 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 T DB T WB T G

 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

◦ Heat Stroke  Ss – core temperature >40 ⁰ C (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

 Preventing Hyperthermia ◦ When possible decrease effort to decrease heat production ◦ Recognize Ss of hyperthermia ◦ When WBGT exceeds 28 ⁰ C (82.4 ⁰ F) do not practice or compete outdoors ◦ Frequent fluid breaks ◦ Appropriate clothing – skin exposure

 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

 Body temperature and heart rate increase to a lesser degree during exercise at any heat load  Decrease rate of glycogen utilization after acclimitization

 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

 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

 Mechanisms: ◦ Shivering ◦ Nonshivering thermogenesis ◦ Peripheral vasoconstriction  Factors to consider in heat loss ◦ Temperature gradient ◦ Surface area ◦ Windchill

 Physiological Responses to Exercise in the Cold ◦ Muscle function ◦ Metabolic responses  Health Risks ◦ Hypothermia ◦ Cardiorespiratory effects

 Increased subcutaneous fat  Greater cold tolerance ◦ Increased blood flow and warming of exposed areas