7-Temperature-Regulation (1).pptx

Scott Scott K. K. Powers Powers Edward Edward T. T. Howley Howley Theory and Application to Fitness and Performance SEVENTH EDITION Chapter Temperature Re...

Scott Scott K. K. Powers Powers Edward Edward T. T. Howley Howley Theory and Application to Fitness and Performance SEVENTH EDITION Chapter Temperature Regulation Chapter 12 Objectives 1. Define the term homeotherm. 2. Present an overview of heat balance during exercise. 3. Discuss the concept of “core temperature.” 4. List the principal means of involuntarily increasing heat production. 5. Define four processes by which the body can lose heat during exercise. 6. Discuss the role of hypothalamus as the body’s thermostat. Chapter 12 Objectives 7. Explain the thermal events that occur during exercise in both a cool/moderate and hot/humid environment. 8. List physiological adaptations that occur during acclimatization to heat. 9. Describe the physiological responses to a cold environment. 10. Discuss the physiological changes that occur in response to cold acclimatization. Chapter 12 Outline  Overview of Heat  Heat Storage in the  Exercise in the Heat Balance During Body During Exercise Sweat Rates During  Body’s Thermostat— Exercise Exercise Hypothalamus Exercise Performance in a  Temperature Hot Environment Shift in the Hypothalamic Measurement During Thermostat Set Point Gender and Age Exercise Due to Fever Differences in  Overview of Heat  Heat Index—A Thermoregulation Heat Acclimatization Production/Heat Loss Measure of How Hot Loss of Acclimatization Heat Production It Feels  Thermal Events During  Exercise in a Cold Heat Loss Environment Exercise Cold Acclimatization Chapter 12 Overview of Heat Balance During Exercise An Overview of Heat Balance Humans are homeotherms – Maintain constant body core temperature – Heat loss must match heat gain Normal core temperature is 37°C – Above 45°C  May destroy proteins and enzymes and lead to death – Below 34°C  May cause slowed metabolism and arrhythmias Thermal gradient from body core to skin surface – Ideal gradient is ~4°C – In extreme cold, may be 20°C Chapter 12 Overview of Heat Balance During Exercise An Overview of Heat Balance Figure 12.1 Chapter 12 Overview of Heat Balance During Exercise In Summary  Homeotherms are animals that maintain a rather constant body core temperature. In order to maintain a constant core temperature, heat loss must match heat gain.  Temperature varies a great deal within the body. In general, there is a thermal gradient from the deep bode temperature (core temperature) to the shell (skin) temperature. Chapter 12 Temperature Measurement During Exercise Temperature Measurement During Exercise Deep-body (core) temperature – Measured at rectum, ear, or esophagus  Usually in laboratory Skin temperature – Thermistors at various locations – Calculate mean skin temperature Tskin = (Tforehead + Tchest + Tforearm + Tthigh + Tcalf + Tabdomen + Tback) ÷ 7 Chapter 12 Temperature Measurement During Exercise In Summary  Measurements of deep-body temperature can be accomplished via mercury thermometers, or devices known as thermocouples or thermistors. Common sites of measurement include the rectum, the ear (tympanic temperature), and the esophagus.  Skin temperature can be measured by placing temperature sensors (thermistors) on the skin at various locations. Chapter 12 Overview of Heat Production/Heat Loss Heat Production Voluntary – Exercise  70–80% energy expenditure appears as heat Involuntary – Shivering  Increases heat production by ~5x – Action of hormones  Thyroxine  Catecholamines  Called nonshivering thermogenesis Chapter 12 Overview of Heat Production/Heat Loss Heat Production Figure 12.2 Chapter 12 Overview of Heat Production/Heat Loss Heat Loss Radiation – Transfer of heat via infrared rays – 60% heat loss at rest – Can be a method of heat gain Conduction – Heat loss due to contact with another surface Convection – Heat transferred to air or water – Example: a fan pushing air past skin Chapter 12 Overview of Heat Production/Heat Loss Heat Loss Evaporation – Heat from skin converts water (sweat) to water vapor  Requires vapor pressure gradient between skin and air – Evaporation rate depends on:  Temperature and relative humidity  Convective currents around the body  Amount of skin surface exposed – Body loses 0.58 kcal heat/L sweat evaporated  1 L sweat results in heat loss of 580 kcal – 25% heat loss at rest  Most important means of heat loss during exercise Chapter 12 Overview of Heat Production/Heat Loss Temperature, Relative Humidity, and Vapor Pressure Chapter 12 Overview of Heat Production/Heat Loss Review methods of heat loss and heat gain?? Chapter 12 Overview of Heat Production/Heat Loss Heat Exchange Mechanisms During Exercise Figure 12.3 Chapter 12 Overview of Heat Production/Heat Loss Heat Storage in the Body During Exercise Heat produced that is not lost is stored in body tissues – Will raise body temperature Body heat gain during exercise = heat produced – heat loss Amount of heat required to raise body temperature – Specific heat of human body is 0.83 kcal/kg Heat required to raise body temp 1°C = specific heat x body mass Chapter 12 Chapter 12 Overview of Heat Production/Heat Loss In Summary  Muscular exercise can result in large amounts of heat production. Since the body is at most 20% to 30% efficient, 70% to 80% of the energy expended during exercise is released as heat.  Body heat can be lost by evaporation, convection, conduction, and radiation. During exercise in a cool environment, evaporation is the primary avenue for heat loss. Chapter 12 Overview of Heat Production/Heat Loss In Summary  The rate of evaporation from the skin is dependent upon three factors: (1) temperature and relative humidity, (2) convective currents around the body, and (3) the amount of skin exposed to the environment.  Body heat storage is the difference between heat production and heat loss.  The amount of heat required to elevate body temperature by 1°C is termed the specific heat of the body. Chapter 12 The Body’s Thermostat—Hypothalamus The Body’s Thermostat—Hypothalamus Anterior hypothalamus – Responds to increased core temperature – Commencement of sweating  Increased evaporative heat loss – Increased skin blood flow  Allows increased heat loss Posterior hypothalamus – Responds to decreased core temperature – Shivering and increased norepinephrine release  Increased heat production – Decreased skin blood flow  Decreased heat loss Chapter 12 The Body’s Thermostat—Hypothalamus Physiological Responses to “Heat Load” Figure 12.4 Chapter 12 The Body’s Thermostat—Hypothalamus Physiological Responses to Cold Stress Figure 12.5 Chapter 12 The Body’s Thermostat—Hypothalamus Shift in Hypothalamic Set Point Due to Fever Fever – Increased body temperature above normal – Due to pyrogens  Proteins or toxins from bacteria – Change in set point of hypothalamus Chapter 12 The Body’s Thermostat—Hypothalamus In Summary  The body’s thermostat is located in the hypothalamus.  The anterior hypothalamus is responsible for reacting to increases in core temperature, while the posterior hypothalamus governs the body’s responses to a decrease in temperature.  An increase in core temperature results in the anterior hypothalamus initiating a series of physiological actions aimed at increasing heat loss. These actions include: (1) the commencement of sweating and (2) an increase in skin blood flow. Chapter 12 The Body’s Thermostat—Hypothalamus In Summary  Cold exposure results in the posterior hypothalamus promoting physiological changes that increase body heat production (shivering) and reduce heat loss (cutaneous vasoconstriction). Chapter 12 Thermal Events During Exercise Thermal Events During Exercise As exercise intensity increases: – Heat production increases – Linear increase in body temperature  Core temperature proportional to active muscle mass – Higher net heat loss  Lower convective and radiant heat loss  Higher evaporative heat loss As ambient temperature increases: – Heat production remains constant – Lower convective and radiant heat loss – Higher evaporative heat loss Chapter 12 Thermal Events During Exercise Changes in Metabolic Energy Production and Heat Loss During Exercise Figure 12.6 Chapter 12 Thermal Events During Exercise Body Temperature During Arm and Leg Exercise Figure 12.7 Chapter 12 Chapter 12 Thermal Events During Exercise Thermal Events During Exercise Increase in body temperature is directly related to exercise intensity – Body heat load increases with intensity Mechanisms of heat loss during exercise – Evaporation  Most important means of heat loss – Convection  Small contribution – Radiation  Small role in total heat loss Chapter 12 Chapter 12 Thermal Events During Exercise In Summary  During constant intensity exercise, the increase in body temperature is directly related to the exercise intensity.  Body heat production increases in proportion to exercise intensity. Chapter 12 Chapter 12 Chapter 12 Chapter 12 Chapter 12 Exercise in the Heat Clinical Applications 12.1 Exercise-Related Heat Injuries Can Be Prevented Guidelines – Exercise during the coolest part of the day – Minimize exercise intensity and duration on hot/humid days – Expose a maximal surface area of skin for evaporation – Provide frequent rests/cool-down breaks with equipment removal – Avoid dehydration with frequent water breaks – Rest/cool-down breaks should be in the shade and offer circulating, cool air Chapter 12 Exercise in the Heat The Winning Edge 12.1 Prevention of Dehydration During Exercise Dehydration of 1–2% body weight can impair performance Guidelines – Hydrate prior to performance  400–800 ml fluid within three hours prior to exercise – Consume 150–300 ml fluid every 15–20 min  Volume adjusted based on environmental conditions – Ensure adequate rehydration  Consume equivalent of 150% weight loss  1 kg body weight = 1.5 L fluid replacement – Monitor urine color Sports drinks are superior to water for rehydration Chapter 12 Exercise in the Heat Exercise Performance in a Hot Environment Can result in muscle fatigue and impaired performance – Reduced mental drive for motor performance – Reduced muscle blood flow – Accelerated glycogen metabolism – Increased lactic acid production – Increased free radical production Chapter 12 Chapter 12 Chapter 12 Exercise in the Heat Heat Acclimatization Requires exercise in hot environment Adaptations occur within 7–14 days – Increased plasma volume – Earlier onset of sweating – Higher sweat rate – Reduced sodium chloride loss in sweat – Reduced skin blood flow – Increased cellular heat shock proteins Acclimatization lost within a few days of inactivity Chapter 12 Chapter 12 Chapter 12 Exercise in the Heat Primary Adaptations of Heat Acclimatization Chapter 12 Exercise in the Heat In Summary  During prolonged exercise in a moderate environment, core temperature will increase gradually above the normal resting value and will reach a plateau at approximately thirty to forty-five minutes.  During exercise in a hot/humid environment, core temperature does not reach a plateau, but will continue to rise. Long-term exercise in this type of environment increases the risk of heat injury.  Heat acclimatization results in: (1) an increase in plasma volume, (2) an earlier onset of sweating, (3) a higher sweat rate, (4) a reduction in the amount of electrolytes lost in sweat, (5) a reduction in skin blood flow, and (6) increased levels of heat shock protein in tissues. Chapter 12 Exercise in a Cold Environment Exercise in a Cold Environment Enhanced heat loss – Reduces chance of heat injury – May result in hypothermia  Loss of judgment and risk of further cold injury Cold acclimatization – Results in lower skin temperature at which shivering begins  Increased nonshivering thermogenesis – Maintain higher hand and foot temperature  Improved peripheral blood flow – Improved ability to sleep in the cold  Due to reduced shivering – Adaptations begin in one week Chapter 12 Exercise in a Cold Environment In Summary  Exercise in a cold environment enhances an athlete’s ability to lose heat and therefore greatly reduces the chance of heat injury.  Cold acclimatization results in three physiological adaptations: (1) improved ability to sleep in cold environments, (2) increased nonshivering thermogenesis, and (3) a higher intermittent blood flow to the hands and feet. The overall goal of these adaptations is to increase heat production and maintain core temperature, which will make the individual more comfortable during cold exposure. Chapter 12 Study Questions 1. Define the following terms: (1) homeotherm, (2) hyperthermia, and (3) hypothermia. 2. Why does a significant increase in core temperature represent a threat to life? 3. Explain the comment that the term body temperature is a misnomer. 4. How is body temperature measured during exercise? 5. Briefly discuss the role of the hypothalamus in temperature regulation. How do the anterior hypothalamus and posterior hypothalamus differ in function? Chapter 12 Study Questions 6. List and define the four mechanisms of heat loss. Which of these avenues plays the most important part during exercise in a hot/dry environment? 7. Discuss the two general categories of heat production in people. 8. What hormones are involved in biochemical heat production? 9. Briefly outline the thermal events that occur during prolonged exercise in a moderate environment. Include in your discussion information about changes in core temperature, skin blood flow, sweating, and skin temperature. Chapter 12 Study Questions 10. Calculate the amount of evaporation that must occur to remove 400 kcal of heat from the body. 11. How much heat would be removed from the skin if 520 ml of sweat evaporated during a thirty-minute period? 12. List and discuss the physiological adaptations that occur during heat acclimatization. 13. How might exercise in a cold environment affect dexterity in such skills as throwing and catching? 14. Discuss the physiological changes that occur in response to chronic exposure to cold.