This chapter discusses temperature regulation during exercise. The body maintains core temperature through balancing heat production and heat loss. It produces heat through voluntary exercise and involuntary processes like shivering. Heat is lost via radiation, conduction, convection and evaporation. The hypothalamus acts as the body's thermostat, regulating responses like sweating and shivering. During exercise in heat, core temperature and sweat rate increase to balance heat. Acclimatization to heat enables higher sweat rates and reduced sodium loss. Cold environments enhance heat loss, while acclimatization improves non-shivering thermogenesis and intermittent blood flow.

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

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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

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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