Lecture 2 (Temperature Regulation)
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Transcript of Lecture 2 (Temperature Regulation)
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Production
Voluntary Exercise
Involuntary Shivering Action of hormones
Thyroxine Catecholamines
Fig 12.2
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Exchange During Exercise
Fig 12.3
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Responses to Heat Stress
Fig 12.4
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Responses to Cold Stress
Fig 12.5
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Exchange During Exercise
Fig 12.6
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Body Temperature During Arm and Leg Exercise
Fig 12.7
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Exchange During Exercise Effect of Ambient Temperature
Fig 12.8
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Exchange During ExerciseEffect of Exercise Intensity
Fig 12.9
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Exercise in Hot/Humid Environments
Inability to lose heat Higher core temperature Higher sweat rate
Can result in: Impaired performance Hyperthermia
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Core Temperature and Sweat Rate During Exercise in Heat/Humidity
Fig 12.10
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
Heat Acclimatization
Increased plasma volume Earlier onset of sweating Higher sweat rate Reduced sodium chloride loss in
sweat Reduced skin blood flow
(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
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