Present Thermal Regulation

8/6/2019 Present Thermal Regulation

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Thermal / Body TemperatureThermal / Body TemperatureRegulationRegulation

Chapter 9Chapter 9

Presented by: Meghann Snyder, Kevin Lavoie,Presented by: Meghann Snyder, Kevin Lavoie,

Professor Steven DionProfessor Steven Dion

Salem State collegeSalem State college

Sport, Fitness & Leisure Studies DepartmentSport, Fitness & Leisure Studies Department


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Chapter 9 2

Without thermoregulation to facilitate exerciseWithout thermoregulation to facilitate exercise

the body would overheat and the effect wouldthe body would overheat and the effect wouldresult in death. Our core body temperature canresult in death. Our core body temperature can

drop 10 degrees and the body can still survive,drop 10 degrees and the body can still survive,

but a core increase of just 5 degrees is all webut a core increase of just 5 degrees is all we

can tolerate.can tolerate.

Many athletes have died of heat stress for thisMany athletes have died of heat stress for this

reason. It is important to know how to cool offreason. It is important to know how to cool off

in hot weather by understandingin hot weather by understanding

thermoregulation and the best ways to make itthermoregulation and the best ways to make it

work to your advantage.work to your advantage.


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Chapter 9 3

Thermal BalanceThermal Balance

A result of body mechanisms which:A result of body mechanisms which:

alter heat transfer to the shellalter heat transfer to the shell

regulate evaporative coolingregulate evaporative cooling

adjust heat productionadjust heat production


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Chapter 9 4


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Chapter 9 5

Factors That Affect Heat GainFactors That Affect Heat Gain

BMR, muscular activity, hormones, thermic effectBMR, muscular activity, hormones, thermic effect

of food, postural changes, and environment. (Totalof food, postural changes, and environment. (Total

metabolic rate can increase 3 to 5 times frommetabolic rate can increase 3 to 5 times from

shivering and 20 to 25 times during sustainedshivering and 20 to 25 times during sustainedvigorous exercise in aerobically fit individuals.vigorous exercise in aerobically fit individuals.

Heat is conserved when blood is shunted into theHeat is conserved when blood is shunted into the

cranial, thoracic and abdominal cavities andcranial, thoracic and abdominal cavities and

portions of muscle mass for insulation from theportions of muscle mass for insulation from the

shell.shell.


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Chapter 9 6

Factors That Affect Heat LossFactors That Affect Heat Loss

Radiation, conduction, convection, andRadiation, conduction, convection, and

evaporation, which is most important.evaporation, which is most important.

The body is cooled when internal heatThe body is cooled when internal heatbuildup causes the blood vessels to dilatebuildup causes the blood vessels to dilate

and direct warm blood to the shell.and direct warm blood to the shell.


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Chapter 9 7

Hypothalamic Regulation ofHypothalamic Regulation of

Core TemperatureCore Temperature The hypothalamus contains the central coordinationThe hypothalamus contains the central coordination

center for temperature regulation. It initiates thecenter for temperature regulation. It initiates theresponses that keep the body from overheating orresponses that keep the body from overheating orovercoolingovercooling

HeatHeat--regulating mechanisms are activated by either:regulating mechanisms are activated by either:

Thermal receptors in the skin or,Thermal receptors in the skin or,

Temperature changes in the bloodTemperature changes in the blood Free nerve endings in the skin respond to heat and coldFree nerve endings in the skin respond to heat and cold

and relay the senses to the hypothalamus and cerebraland relay the senses to the hypothalamus and cerebralcortex.cortex.


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Chapter 9 8

Thermoregulation in HeatThermoregulation in Heat

Stress: Heat LossStress: Heat Loss The body's thermoregulatory mechanismsThe body's thermoregulatory mechanisms

primarily protect against overheating.primarily protect against overheating.

Body heat loss occurs in four ways:Body heat loss occurs in four ways: (page 271)(page 271) radiationradiation

conduction,conduction,

convection,convection, evaporationevaporation


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Chapter 9 9

Heat Loss by RadiationHeat Loss by Radiation

Our bodies are usually warmer than theOur bodies are usually warmer than the

environment, so the air and the objectsenvironment, so the air and the objects

around us absorb our body heat.around us absorb our body heat.


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Chapter 9 10

Heat Loss by ConductionHeat Loss by Conduction

Heat loss by conduction involves the directHeat loss by conduction involves the direct

transfer of heat through a liquid, solid, ortransfer of heat through a liquid, solid, or

gas from one molecule to another.gas from one molecule to another. The rate of conductive heat loss depends onThe rate of conductive heat loss depends on

the temperature gradient between the skinthe temperature gradient between the skin

and surrounding surfaces and their thermaland surrounding surfaces and their thermal

qualitiesqualities


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Chapter 9 11

Heat Loss by ConvectionHeat Loss by Convection

On a breezy day, cooler air continuallyOn a breezy day, cooler air continually

replaces the warm air around the body, soreplaces the warm air around the body, so

heat loss increases because the air currentsheat loss increases because the air currentscarry the heat away.carry the heat away.


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Chapter 9 12

Heat Loss by EvaporationHeat Loss by Evaporation

Water vaporization from the respiratoryWater vaporization from the respiratory

passages and skin surface continuallypassages and skin surface continually

transfers heat to the environmenttransfers heat to the environment


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Chapter 9 13


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Chapter 9 14

Evaporative Heat Loss atHighEvaporative Heat Loss atHigh

Ambient TemperaturesAmbient Temperatures Increased temperatures reduces theIncreased temperatures reduces the

effectiveness of heat loss by conduction,effectiveness of heat loss by conduction,

convection, and radiation.convection, and radiation. When temperatures exceed the body'sWhen temperatures exceed the body's

temperature, these mechanisms contributetemperature, these mechanisms contribute

to heat gain.to heat gain.

When this occurs, the only avenue toWhen this occurs, the only avenue to

dissipate heat is through evaporation.dissipate heat is through evaporation.


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Chapter 9 15

Heat Loss in High HumidityHeat Loss in High Humidity

Sweat evaporation depends on 3 things:Sweat evaporation depends on 3 things:

Surface exposed to the environmentSurface exposed to the environment

Temperature and relative humidity ofTemperature and relative humidity ofambient airambient air

Convective air currents around the bodyConvective air currents around the body

Relative humidity exerts the greatest impact.Relative humidity exerts the greatest impact.


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Chapter 9 16

Effects ofClothing onEffects ofClothing on

Thermoregulation in the HeatThermoregulation in the Heat Dry clothing retards heat exchange, because if youDry clothing retards heat exchange, because if youswitch to a dry shirt you do not let evaporative coolingswitch to a dry shirt you do not let evaporative coolingtake effect. (Sweating doesnt cool you, evaporationtake effect. (Sweating doesnt cool you, evaporationdoes.)does.)

Heavy sweat shirts and rubber or plastic clothing causeHeavy sweat shirts and rubber or plastic clothing causehigh humidity near the skin and also retard evaporativehigh humidity near the skin and also retard evaporativecooling.cooling.

Loose clothing is recommended for evaporation since itLoose clothing is recommended for evaporation since itpermits the free convection of air between the skin andpermits the free convection of air between the skin andenvironment.environment.

Light clothing to reflect light is recommended opposedLight clothing to reflect light is recommended opposedto dark which absorbs itto dark which absorbs it


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Chapter 9 17

Football UniformsFootball Uniforms

Football gear causes a major barrier to heatFootball gear causes a major barrier to heatdissipation and seals off 50% of the skin fromdissipation and seals off 50% of the skin fromevaporative cooling.evaporative cooling.

The weight of the gear also makes the musclesThe weight of the gear also makes the musclesproduce more heatproduce more heat

Large players also have a small surface area toLarge players also have a small surface area to

mass ratio and more body fatmass ratio and more body fat Football has had many heat related deaths in theFootball has had many heat related deaths in the

past 20 yearspast 20 years


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Chapter 9 18

The Modern Cycling Helmet doesThe Modern Cycling Helmet does

not ThwartHeat Dissipationnot ThwartHeat Dissipation

Modern helmets are lightweight,Modern helmets are lightweight,aerodynamic, and ventilated.aerodynamic, and ventilated.

They do not keep heat from escapingThey do not keep heat from escaping

through the head.through the head.

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Present Thermal Regulation