Presentation on theme: "Exercise Thermoregulation, Fluid Balance, and Rehydration Chapter 10 Part 1."— Presentation transcript:
Exercise Thermoregulation, Fluid Balance, and Rehydration Chapter 10 Part 1
Temperature Regulation Body core temperature regulation –Critical for: Cellular structures Metabolic pathways –Too high - hyperthermia(5 o C) Protein structure of cells destroyed –Too low – hypothermia (10 o C) Slowed metabolism Cardiac arrhythmias
Temperature Regulation Thermal gradients –Determine rate and direction of heat transfer –Heat transfer from higher to lower temperature –Core to shell (skin) Typical gradient when ambient temp is less than body temp –Skin to core If ambient temperature is Greater than body temp
Temperature Regulation Net gain of body heat –Heat loss is less than heat production –Body temperature rises –Positive thermal balance Net loss of body heat –Heat loss exceeds heat production –Body temperature decreases –Negative thermal balance
Temperature Regulation Homeotherms (mammals) –Internal body temperature is kept fairly constant Humans are unable to tolerate wide changes Hour to hour, day to day variations < 1 o C Normal temperature: 37 o C Normal range 36.1 – 37.8 o C (97 – 100 o F) –Conversion: Tf = (Tc * 1.8) + 32 –So, if it is 37 o C, Tf = (37 * 1.8) + 32 – = 98.6 o F –Heavy exercise, illness, extreme conditions of heat and cold – can push an individual outside this range
Heat Balance Greater extremes –Early morning (<36 o C) –Heavy exercise >40 o C Muscles >42 o C or o F Body temperature (core temperature) reflects the balance between heat production and heat loss
Body Temperature Core body temperature: deep tissues Skeletal muscles and organs Shell body temperature: peripheral Skin Initiate response to external temperature Thermoreceptors relay information to Hypothalamus Cerebral cortex
Hypothalamic Regulation Hypothalamus (37 1 o C) Central coordinating center Acts as a thermostat Heat gain Heat loss
Heat-Regulating Mechanisms Activated by: Temperature changes in blood Skin heats up/cools down changes temperature of blood Directly stimulate hypothalamus Thermal receptors in the skin Provide input to modulate hypothalamic activity. Receptors (temperature regulation) Skin Subcutaneous tissue.
Radiation Objects “radiate” heat Body temperature is warmer than the environment. Radiant heat energy transfers to solid cooler objects around us. Body temperature is cooler than the environment. Radiant heat energy transfers to us.
Conduction Transfers heat directly through a liquid, solid, or gas from one molecule to another We conduct heat to cooler air, water or objects Warmer air, water or objects conduct heat to us
Convection Air, water movement So, if cool/hot air is travelling over the body (e.g. wind) or cool/hot water, we will be cooled/heated
Evaporation Major physiologic defense against overheating Respiratory water loss Sweat Heat stress 2-4 million sweat (eccrine) glands Secrete large quantities of hypotonic saline solution. *Cooling occurs when sweat evaporates from the skin surface. Has to evaporate
Environmental Temperature Increased ambient temperature Reduces heat loss by conduction, convection, and radiation. This heat loss stops when ambient temp exceeds body temp At that point, the only way to dissipate heat is Sweat evaporation from the skin depends upon: Surface exposed to the environment relative humidity of ambient air Convective air currents around the body
Heat-Dissipating Mechanisms Circulation Cardiac output (HR x SV) Rest – 15-20% to skeletal muscles Heavy exercise – 80-85% to skeletal muscles “Workhorse” to maintain thermal balance 15-25% of cardiac output – periphery If cardiac output falls, skin blood flow falls and ability to dissipate heat is reduced So, when exercising in the heat Cardiac output is directed more to periphery Less to muscle Cause of fatigue
Fluid conserving Mechanisms Hormones Antidiuretic hormone - ADH (Vasopressin) Posterior Pituitary Increases water reabsorption from kidneys Conserves water and maintains BP Aldosterone Adrenal cortex Increases reabsorption of sodium
Heat-related Deaths Since 1936 (National Safety Council) –30,000 people have died from heat related illnesses. On the average, 384 people die each year from heat stroke. –Associated with normal hot temperatures. –In the event of a heat wave, the number of deaths increase tremendously. Occurrence of heat related injuries –Often with the elderly; –People who are not in good physical condition; –or not acclimatized to the heat –Or heat waves
Exercise in the Heat Increased heat load Increased sweating Increased Fluid loss –Decreased plasma volume –Decreased cardiac output –Decreased cutaneous circulation
Distribution of Cardiac Output Thermoneutral environment vs hot environment
Water Loss Dehydration Sweat loss 0.5 – 1.5 L/h – moderate exercise –Maximal daily sweat rates L –Highest sweat rates 2 to 3 L/hr Can be sustained for only a few hours Considerable water loss Both intracellular and extracellular compartments The risk of heat illness Increases in a dehydrated state.
Sweat Rates 1 to 3% loss in body weight through dehydration can adversely affect performance and body’s physiologic function Marathon runners –Loss of 5 L –6-10% of body weight
Core Temperature and Sweat Rate During Exercise in Heat/Humidity Fig 12.10
Exercise in the Heat Compromised BF to muscles Increased use of glycogen Increased production of LA Hastens fatigue
Dehydration and Exercise Performance
Any degree of dehydration impairs Capacity of circulatory system Temperature-regulating mechanisms Dehydration - 2% body mass Impairs physical work capacity and physiologic function Predisposes to heat injury when exercising in a hot environment.
Dehydration and Exercise Performance The risk for dehydration increases during vigorous cold-weather exercise. Less moisture in cold Respiratory fluid loss is increased Excessive clothing Creates a heated microclimate under the clothing