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Chapter 12 Temperature Regulation

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1 Chapter 12 Temperature Regulation
EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

2 Objectives Define tem homeotherm
Present an overview of heat balance during exercise Discuss the concept of “core temperature” List the principle means of involuntarily increasing heat production Define four processes by which the body can lose heat during exercise Discuss the role of hypothalamus as the body’s thermostat

3 Objectives Explain the thermal events that occur during exercise in both a cool/moderate and hot/humid environment List physiological adaptations that occur during acclimatization to heat Describe physiological responses to a cold environment Discuss physiological changes that occur in response to cold acclimatization

4 An Overview of Heat Balance
In order to maintain a constant core temperature, heat loss must match heat gain Thermal gradient from body core to skin surface Fig 12.1

5 Temperature Measurement During Exercise
Deep-body (core) temperature Thermocouples or thermistors Rectum, ear, and esophagus Skin temperature Thermistors at various locations Calculate mean skin temperature

6 Heat Production Voluntary Exercise Involuntary Shivering
Action of hormones Thyroxine Catecholamines Fig 12.2

7 Heat Loss Radiation Transfer of heat via infrared rays
No physical contact between surfaces 60% heat loss at rest Conduction Heat loss due to contact with another surface

8 Heat Loss Convection Form of conductive heat loss
Heat transferred to air or water Evaporation Heat transferred via water (sweat) on skin surface Evaporation rate depends on: Temperature and relative humidity Convective currents around the body Amount of skin surface exposed 25% heat loss at rest Most important means during exercise

9 Heat Exchange During Exercise
Fig 12.3

10 The Hypothalamus: The Body’s Thermostat
Increased core temperature Anterior hypothalamus Commencement of sweating Increased skin blood flow Cold exposure Posterior hypothalamus Increase heat production Shivering Decrease heat loss Decreased skin blood flow

11 Responses to Heat Stress
Fig 12.4

12 Responses to Cold Stress
Fig 12.5

13 Heat Exchange During Exercise
Metabolic energy (heat) production stimulates heat loss Evaporative heat loss Most important means of heat loss Convective heat loss Small contribution Radiative heat loss Small role in total heat loss

14 Heat Exchange During Exercise
Fig 12.6

15 Body Temperature Increase During Exercise
Increase in body temperature with work rate Linear across wide range of temperatures Linear for both arm and leg exercise Temperature proportional to active muscle mass

16 Body Temperature During Arm and Leg Exercise
Fig 12.7

17 Heat Exchange During Exercise Effect of Ambient Temperature
As ambient temperature increases, Heat production remains constant Lower convective and radiant heat loss Higher evaporative heat loss

18 Heat Exchange During Exercise Effect of Ambient Temperature
Fig 12.8

19 Heat Exchange During Exercise Effect of Exercise Intensity
With increased exercise intensity Heat production increases Higher net heat loss Lower convective and radiant heat loss Higher evaporative heat loss

20 Heat Exchange During Exercise Effect of Exercise Intensity
Fig 12.9

21 Exercise in Hot/Humid Environments
Inability to lose heat Higher core temperature Higher sweat rate Can result in: Impaired performance Hyperthermia

22 Core Temperature and Sweat Rate During Exercise in Heat/Humidity
Fig 12.10

23 Heat Acclimatization Increased plasma volume Earlier onset of sweating
Higher sweat rate Reduced sodium chloride loss in sweat Reduced skin blood flow

24 Exercise in a Cold Environment
Enhanced heat loss Reduces chance of heat injury May result in hypothermia Cold acclimatization Improved ability to sleep in the cold Increased nonshivering thermogenesis Higher intermittent blood flow to hands and feet Results in ability to maintain core temperature

25 Chapter 12 Temperature Regulation

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