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