Lecture 2 (Temperature Regulation)

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LECTURE 2:Temperature Regulation

PHYSIOLOGY OF PHYSICAL ACTIVITIES

Adapted from

Theory and Application to Fitness and Performance, 5th edition

Scott K. Powers & Edward T. HowleyPresentation revised and updated by

Dr MOHD SANI MADON (PhD)

Universiti Pendidikan Sultan Idris

2007-2008

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Objectives

Define term 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 & 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 HypothalamusThe 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 ExerciseEffect 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 non-shivering thermogenesis Higher intermittent blood flow to hands and

feet Results in ability to maintain core temperature