Thermoregulation Exercise in Hot and Cold Environments Mgr. Tereza Brůžová Learning objectives ■ Why do we need to regulate body temperature? ■ How do we regulate body temperature - mechanisms of heat transfer ■ How our body gets rid of excess heat? ■ How our body minimizes heat loss in cold environments? ■ Do factors such as humidity, wind and cloud cover impact when exercising in hot environment? Thermoregulation ■ Humans are endothermic organisms ■ Keep their body temperature within certain range even if the temperature of the environment changes significantly ■ Metabolic processes as a heat source ■ Most heat in generated in the liver, brain, heart, and in skeletal muscles ■ We have systems that decrease or increase our body temperature as needed ■ Ectothermic organisms use external energy sources to regulate body temperature Thermoregulation ■ Is the ability of an organism to control its body temperature 1 Why is it important? Thermoregulation ■ Is the ability of an organism to control its body temperature ■ Temperature influences the speed of biochemical processes Substrate, which is a complementary the optimum temperature is reached, shape to the enzyme active site where the reaction occurs at its fastest / 0 10 20 30 40 50 60 temperature °C © ABPI 2015 Heat Transfer A. Radiation - Heat transfer through infrared rays which are emitted by all objects with temperature above absolute zero; approx. 60% of heat transfer (HT) evaporace (22 %) B. Convection - Heat transfer through air flow; approx. 15% of HT; quicker transfer in windy environments D. Evaporation - Crucial when temperature of the environment is higher than body temperature, its efficacy depends on humidity; at rest approx. 20%, during exercise up to 80% of HT; around 450-800 ml per day; 580 kcal/L vedení objekty, kterých se dotýkáme (3 %) C. Conduction - Heat transfer through direct molecular contact with an object; approx. 3% of HT Heat Transfer Rest Exercise Mechanism of heat loss % total kcal/min % total kcal/min Conduction and convection 20 Radiation 60 Evaporation 20 Total 100 0.3 15 2.2 0.9 5 0.8 0.3 80 12.0 1.5 100 15.0 Heat Transfer Skin and Heat Transfer Sweat gland Heat in blood Surface of 1.5-1.8 m2 Mass around 4.5 kg Epidermis Dermis i Subcutaneous-layer Papillary layer Reticular layer shaft Sweat pore Epidermal ridge Dermal papilla Arrector pili muscle Sebaceous (oil) gland Sweat gland duct Merocrine sweat gland Vein Artery Adipose connective tissue Hair follicle Sensory Areolar Sensory receptors connective tissue nerve fiber Source: Mescher AL: Junqueira's Basic Histology: Text and Atlas, 12th Edition: http://www.3ccessmedicine.com Copyright © The McGraw-Hill Companies, Inc. All rights reserved. Body Temperature ■ At rest, the temperature is kept around 37 °C ■ When exercising it can exceed 40 °C (104 °F) ■ Can raise up to 42 °C (107.6 °F) in active muscles ■ Small increases can make their function more efficient ■ Too high temperature can cause affect the nervous system, can cause enzyme denaturation the optimum temperature is reached, where the reaction occurs at its fastest Before (left) and after (right) running outside at 30° C (75% humidity) 0 0S00"C 27 250"C ■ Iff! \ 1 ■ 37 450X the rate of reaction increases as the temperature increases Body Temperature Assessment ■ Is assessed from skin temperature (Tskin) and core temperature (Tr) " Tbody = (0.4 x Tskin) + (0.6 x Tr) Heat Content ■ Total calories of heat contained in body tissues ■ Average specific heat of body tissues is 0.83 kcal x kg-1 x °C_1 ■ Heat content = 0.83 (Body weight x Tbody) ■ Heat produced by average body at rest is 1.25 to 1.5 kcal per minute ■ Heat produced during exercise can exceed 15 kcal per minute ■ This heat must be dissipated by the body's thermoregulatory systems Thermoregulation Control 1. By preoptic area of the anterior hypothalamus = "thermostat' 2. Central and peripheral thermoreceptors 3. Effectors a) Sweat glands b) Smooth muscles around arterioles c) Skeletal muscle d) Endocrine glands Hypothalamus Control 3. Effectors Warn up Weenanisns our body uses: Cool down Sweat production Vasodilation, Vasoconstriction Shivering Goosebumps «- CONSERVE H£RT «• GENERATE mOR£ .CONTRACT ERECTOR RUSClES (IfiYER of insuirtimg air) CONSTRICT (vrsocomstrictiom) s h£rt £n£rgv is iqst Energy FROn RESPIRATION HEAT ENERGY AS WASTE muSClES CONTRACT AUTOMATICALLY The opposite: SWEAT -TRkES H£RT ENERGY RU1RV WITH IT ERECTOR miASClES RELAX £xPAMO (VASODILATE) nOR£ h£at £n£rgy TRANSFERRED TO SURROUNDINGS 3. Effectors ■ Sweat production ■ Vasodilation, Vasoconstriction ■ Shivering ■ Goosebumps Pores ■ As body temperature rises the production of sweat increases ■ Sweat evaporates when it reaches skin ■ Accounts for up to 80% of heat loss during exercise 3. Effectors ■ Sweat production ■ Vasodilation, Vasoconstriction ■ Shivering ■ Goosebumps 3. Effectors ■ Sweat production ■ Vasodilation, Vasoconstriction ■ Shivering ■ Goosebumps Dermal Circulation Exercising in Hot and Cold Environments HOT environments Exercising in Hot Environment Cardiovascular response: ■ Active muscies and skin compete for blood supply ■ Stroke volume decreases ■ Heart rate gradually increases to compensate for lower SV (cardiovascular drift) Exercising in Hot Environment Metabolic Response: Body Temperature u Oxygen Uptake X Glycogen Depletion Muscle Lactate \J 6 Sweating \J / High volumes of sweat cause: ■ Decreased blood volume ■ Loss of minerals and electrolytes ■ Release of aldosterone and ADH and water reabsorption in kidneys Loss of ions through sweat during exercise Subjects Sweat Na+ (mmol/L) Sweat CI" (mmol/L) Sweat K+ (mmol/L) Untrained males 90 60 4 Trained males 35 30 4 Untrained females 105 98 4 Trained females 62 Data from the Human Performance Laboratory, Ball State University 47 4 Variables Affecting Environmental Heat Load Air Temperature Humidity Air Flow Velocity Thermal Radiation Temperature control in hot environment ■ When temperature of the environment is higher than your body temperature "'"environment ^ ~^body ■ You gain heat from radiation, convection, and conduction. EVAPORATION becomes the oniy way of heat ioss Temperature control in hot environment ■ When temperature of the environment is higher than your body temperature "'"environment ^ ~^body ■ You gain heat from radiation, convection, and conduction. EVAPORATION becomes the oniy way of heat ioss ■ The efficacy of evaporation is Limited by HUMIDITY - The higher the humidity the slower the evaporation ■ Excessive sweating may lead to dehydration, reduced plasma volume and increased Tbody Excessive sweating ■ Reduced blood amounts hinder heat loss through capillaries ■ Fluid intake is especially important when exercising in hot environment Wet Bulb Globe Temperature (WBGT) Measures the heat stress in direct sunlight BLACK GLOBE Considers temperature, humidity, wind speed, sun angie and soiar radiation (cloud cover) Wet Bulb How the wet bulb temperature works Dry bulb temperature Wet bulb temperature Wet Bulb Globe Temperature Dry bulb measures air temperature (TDB) Wet bulb measures temperature as water evaporates from it (TWB) Black globe absorbs radiated heat (TG) WBGT = 0.1TDB + 0.7TWB + 0.2TG Thermometer for evaporative water loss Thermometer for globe temperature a. Thermometer for air temperature Warning Signs of Heat Disorders Headache and nausea Warning signs Heat illness ^ Thirst Profuse sweating Fatigue Chills or goose bumps Cessation ot sweating Faintness or dizziness Muscle cramps Strong and rapid pulse Hot and dry skin Heat cramps ■ Heat exhaustion Increasing severity Contusion Heat stroke Treatment of Heat Disorders = Hyperthermia A group of illnesses caused by prolonged exposure to hot temperatures, restricted fluid intake, or failure of the body's ability to regulate its temperature ■ Heat cramps ■ the least severe; warning sign that more serious problems may develop ■ 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 (liquid with electrolytes) ■ Results from the cardiovascular system being unable to meet the needs of muscles and skin due to lower blood volume (from sweating) ■ Heat stroke ■ Immediate medical treatment vitally important!!! ■ Failure of the thermoregulatory system ■ rapidly cool body in cold water, ice bath or with wet towels Subjective Symptoms Associated with Overheating Rectal temperature Symptoms 40-40.5° C (104-105° F) Cold sensation over stomach and back with piloerection (goose bumps) 40.5-41.1° C (105-106° F) Muscular weakness, disorientation, and loss of postural equilibrium 41.1-41.7° C (106-107° F) Diminished sweating, loss of consciousness and hypothalamic control >42.2° C (> 108° F) Death Preventing Hyperthermia ■ Avoid exercising in hot and humid conditions above a WBGT index of 28° C (82.4° F) ■ Schedule practices or events in early morning or at night ■ Wear light-weight, light-colored, loosely-woven clothing ■ Drink plenty fluids ■ Know the symptoms of heat stress ot_____ 0 30 60 90 120 150 Running time (min) Heat Acclimatization ■ With exercise the ability to get rid of excess heat improves ■ Sweat sooner, sweat glands produce a greater volume of sweat, and the sweat is more dilute (less concentrated) ■ Reduced blood flow to skin; more available to muscle ■ Blood volume increases ■ Heart rate increases more slowly ■ Stroke volume increases ■ Muscle glycogen usage decreases 41 - Unacclimatized —■— - Heat acclimatized 0 30 60 90 a Exercise time (min) 200 190 180 0 30 60 90 b Exercise time (min) Heat Acclimatization 41 40 O is 39 E "to o 38 CD 37 0 l 200 190 180 170 g 160 € 150 g 140 130 120 0 Unacclimatized Heat acclimatized 30 60 Exercise time (min) 90 30 60 Exercise time (min) 90 COLD environments How does the Body Conserve Heat? ■ SHIVERING - rapid involuntary cycle of contraction and relaxation of muscles ■ NONSHIVERING THERMOGENESIS - stimulation of metabolism to produce heat (BAT - brown adipose tissue) ■ PERIPHERAL VASOCONSTRICTION - to reduce blood flow close to skin thus minimizing heat exchange with the environment ■ Warming of inspired air - paranasal sinuses What Affects Body Heat Loss? ■ Body size ■ Air temperature ■ Wind chili ■ Water immersion Water —o— 25.6° C —o— 17.4° C Air —o— 23.0° C —□— 23.0° C Swimming ( feline -5 0 5 10 15 20 25 30 35 40 45 50 Exercise duration (min) Responses to Exercise in the Cold ■ Muscle weakens and fatigue occurs more rapidly ■ Susceptibility to hypothermia increases ■ Exercise-induced FFA mobilization is impaired due to vasoconstriction of subcutaneous blood vessels Health Risks of Exercise in the Cold Ability to regulate body temperature is lost if Tbody drops below 34.5° C (94.1° F) Hypothermia causes heart rate to drop, which reduces cardiac output Vasoconstriction in the skin reduces blood flow to skin, eventually causing frostbite Skin without cold damage. STAGES OF FROSTBITE Frostnip Mild frostbite that irritates the skin, causing redness and a cold feeling followed by numbness. Superficial frostbite Skin feels warm, a sign of serious skin involvement. A fluid-filled blister may appear 24 to 36 hours after rewarming the skin. SYMPTOMS OF FROSTBITE At first, cold skin and a prickling feeling Numbness Red, white, bluish-white or grayish-yellow skin Hard or waxy-looking skin Clumsiness due to joint and muscle stiffness Blistering after rewarming, in severe cases You may experience numbness. Joints or muscles may no longer work. Large blisters form 24 to 48 hours after rewarming. Afterward, the area turns black and hard. KEY POINTS ■ Body temperature is regulated for all biochemical processes to run at an optimal speed - low temperature means slower processes, too high temperature can cause damage (denaturation of enzymes) ■ Means of heat transfer - Conduction, convection, radiation, evaporation ■ Body temperature is kept around 37 °C at rest ■ Hypothalamus is the center of thermoregulation ■ Mechanisms such as sweat production, vasoconstriction and vasodilation, shivering and goosebumps for heat loss and heat conservation KEY POINTS ■ Humidity - affects sweating ■ HOT environment - evaporation is the main mechanism of heat loss, mechanisms of heat loss - vasoconstriction and vasodilation ■ Heat stress, WBGT ■ Dry and wet bulb temperature, black globe temperature ■ Heat disorders - heat cramps, heat exhaustion, heat stroke ■ Acclimatization to hot environment ■ COLD environment - mechanisms of conserving heat Thank you 0