1. © 2007 McGraw-Hill Higher Education. All rights reserved.
Chapter 12
Temperature Regulation
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 6th
edition
Scott K. Powers & Edward T. Howley

2. © 2007 McGraw-Hill Higher Education. All rights reserved.
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. © 2007 McGraw-Hill Higher Education. All rights reserved.
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

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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

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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

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

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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

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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

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Heat Exchange During Exercise
Fig 12.3

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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

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Responses to Heat Stress
Fig 12.4

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Responses to Cold Stress
Fig 12.5

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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

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Heat Exchange During Exercise
Fig 12.6

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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

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Body Temperature During
Arm and Leg Exercise
Fig 12.7

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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

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Heat Exchange During Exercise
Effect of Ambient Temperature
Fig 12.8

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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

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Heat Exchange During Exercise
Effect of Exercise Intensity
Fig 12.9

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

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

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

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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

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Chapter 12
Temperature Regulation