EXERCISE IN HOT AND COLD ENVIRONMENTS: THERMOREGULATION chapter 10.tif 0000014DE2862 Wilmore PP BB8DFF79: 85008.jpg 000A2885 PROJECTS 1 B727F70A: BODY HEAT GAINED AND LOST 83231/e2862 000002BBE2862 Wilmore PP B5AE00F7: Modes of Heat Transfer Conduction—direct molecular contact with an object Convection—motion of gas or liquid across heated surface Radiation—infrared rays Evaporation—as fluid evaporates, heat is lost (580 kcal/L) D:\Alternate Chapter Clipart\Chapter 10\Radiation.tiff HEAT REMOVAL FROM THE SKIN 83232/e2862 000002BBE2862 Wilmore PP B5AE00F7: THERMOGRAMS Before running outside at 30° C (75% humidity) Front Before After Back After running outside at 30° C (75% humidity) Before After Evaporation w As body temperature rises, sweat production increases. w Sweat reaches the skin and evaporates. w Evaporation accounts for 80% of heat lost during exercise, but only for about 20% at rest. D:\Alternate Chapter Clipart\Chapter 10\Raindrops.tiff w Insensible water loss removes about 10% of heat. w Dehydration is a potential problem with sweating. Estimated Caloric Heat Loss at Rest and During Prolonged Exercise Conduction and convection 20 0.3 15 2.2 Radiation 60 0.9 5 0.8 Evaporation 20 0.3 80 12.0 Total 100 1.5 100 15.0 Mechanism of heat loss % total kcal/min % total kcal/min Rest Exercise MECHANISMS FOR HEAT BALANCE 83235new/e2862 000004E5E2862 Wilmore PP B5AE00F7: Humidity w Plays a major role in heat loss w Affects our perception of thermal stress w When high (regardless of temperature), limits evaporation of sweat D:\Alternate Chapter Clipart\Chapter 10\Womantennis.tiff Internal Body Temperature w Can exceed 40 °C during exercise w May be 42 °C in active muscles w Small increases can make muscles' energy systems more efficient w Above 40 °C can affect the nervous system and reduce the ability to unload excess heat D:\Alternate Chapter Clipart\Chapter 10\Thermometer2.tiff Regulators of Heat Exchange Hypothalamus Central and peripheral thermoreceptors w Sweat glands w Smooth muscle around arterioles w Skeletal muscles w Endocrine glands Effectors D:\Alternate Chapter Clipart\Chapter 10\Skin.tiff HYPOTHALAMUS AND HYPERTHERMIA 83236/e2862 000002BBE2862 Wilmore PP B5AE00F7: HYPOTHALAMUS AND HYPOTHERMIA 83237/e2862 000002BBE2862 Wilmore PP B5AE00F7: Body Temperature Assessments Mean body temperature (Tbody) is the weighted average of w Skin temperature (Tskin) w Core temperature (Tr) Tbody = (0.4 ´ Tskin) + (0.6 ´ Tr) D:\Alternate Chapter Clipart\Chapter 10\Thermometer.tiff Rate of Heat Exchange w Heat produced by average body at rest is 1.25 to 1.5 kcal per minute. w Heat produced during exercise can exceed 15 kcal per minute. w This heat must be dissipated by the body’s thermoregulatory systems. D:\Alternate Chapter Clipart\Chapter 10\Soccer.tiff w 1 kcal = 4.185 kJ Cardiovascular Response to Exercise in the Heat w Active muscles and skin compete for blood supply. w Stroke volume decreases. w Heart rate gradually increases to compensate for lower SV (cardiovascular drift). D:\Alternate Chapter Clipart\Chapter 13\FootballQB.tiff Metabolic Responses to Exercise in the Heat w Body temperature increases. w Oxygen uptake increases. w Glycogen depletion is hastened. w Muscle lactate levels increase. D:\Alternate Chapter Clipart\Chapter 10\Volleyballserve.tiff w Metabolism speeds up. Body Fluid and Exercise in the Heat w Sweating increases. w High volumes of sweat cause – Blood volume to decrease, – Loss of minerals and electrolytes, and – Release of aldosterone and ADH and water reabsorption in kidneys. D:\Alternate Chapter Clipart\Chapter 15\Rugby.tiff EXERCISE IN HEAT AND COLD 83238/e2862 000002BBE2862 Wilmore PP B5AE00F7: 83239/e2862 000002BBE2862 Wilmore PP B5AE00F7: ECCRINE SWEAT GLAND 83240/e2862 000002BBE2862 Wilmore PP B5AE00F7: Body Temperature Control D:\Alternate Chapter Clipart\Chapter 10\Thermometer.tiff When Tenvironment > Tskin you start gaining heat from w Radiation (e.g., sun, pavement) w Convection (e.g., air) w Conduction (e.g., pavement) Evaporation requires sweating, and excessive sweating leads to dehydration, reduced plasma volume, and increased Tbody . You need more blood volume in skin to lose heat, but there is insufficient blood to do everything. Evaporation then becomes the only avenue of heat loss. Thus when you are in an environment with high humidity, evaporation is limited. Sodium, Chloride, and Potassium Concentrations in the Sweat of Trained and Untrained Subjects During Exercise Untrained males 90 60 4 Trained males 35 30 4 Untrained females 105 98 4 Trained females 62 47 4 Sweat Na+ Sweat Cl– Sweat K+ Subjects (mmol/L) (mmol/L) (mmol/L) Data from the Human Performance Laboratory, Ball State University Variables Affecting Environment Heat Load w Air temperature w Humidity—desert versus tropics w Air velocity—still air versus moving air w Amount of thermal radiation—e.g., cloud cover, ground D:\Alternate Chapter Clipart\Chapter 10\Surfer.tiff WARNING SIGNS OF HEAT DISORDERS 83242/e2862 000002BBE2862 Wilmore PP B5AE00F7: Treatment of Heat Disorders Heat cramps—move to cooler location and administer fluids or saline solution Heat exhaustion—move to cooler environment, elevate feet; give saline if conscious or intravenous saline if unconscious Heat stroke—rapidly cool body in cold water, ice bath or with wet towels; immediately seek medical attention FLUID INTAKE AND EXERCISING IN THE HEAT 83243/e2862 000002BBE2862 Wilmore PP B5AE00F7: Heat Acclimatization w Ability to get rid of excess heat improves w Sweat sooner, sweat glands produce a greater volume of sweat, and the sweat is more dilute (less concentrated) w Reduced blood flow to skin; more available to muscle w Blood volume increases w Heart rate increase is less (than nonacclimatized) w Stroke volume increases w Muscle glycogen usage decreases HEAT ACCLIMATIZATION 83244/e2862 000002BBE2862 Wilmore PP B5AE00F7: 83245/e2862 000002BBE2862 Wilmore PP B5AE00F7: Did You Know…? You can achieve heat acclimatization by exercising in the heat for 1 hour or more each day for 5 to 10 days. Cardiovascular adaptations occur within the first 3 to 5 days while changes in sweating mechanisms may take up to 10 days. Reduce exercise intensity to 60% to 70% the first few days before resuming more intense workouts. D:\Alternate Chapter Clipart\Chapter 06\Runningwoman.tiff How Does the Body Conserve Heat? Shivering—rapid involuntary cycle of contraction and relaxation of muscles Nonshivering thermogenesis—stimulation of metabolism Peripheral vasoconstriction—reduces blood flow to skin D:\Alternate Chapter Clipart\Chapter 10\Snowflake.tiff Factors That Affect Body Heat Loss w Body size and composition w Air temperature w Wind chill w Water immersion D:\Alternate Chapter Clipart\Chapter 10\Snowboarder.tiff WARMING OF INSPIRED AIR 83247new/e2862 000004E5E2862 Wilmore PP B5AE00F7: Responses to Exercise in the Cold w Muscles weaken and fatigue occurs more rapidly w Susceptibility to hypothermia increases w Exercise-induced free fatty acids mobilization is impaired due to vasoconstriction of subcutaneous blood vessels D:\Alternate Chapter Clipart\Chapter 10\Skiing.tiff Health Risks of Exercise in the Cold w Ability to regulate body temperature is lost if Tbody drops below 34.5° C. w Hypothermia causes heart rate to drop, which reduces cardiac output. w Vasoconstriction in the skin reduces blood flow to skin, eventually causing frostbite. D:\Alternate Chapter Clipart\Chapter 10\Snowflakes.tiff