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Heat transfers and hot conditions P1

BND Sport Yr 2

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Aims:

Last lesson• We defined key terms and• Set the basics of thermoregulation.

This lesson we will look at :• The different types of heat transfer.• How the body can maximise heat loss in hot

conditions.

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Task:

List different ways that heat can be

transferred.

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The transfer of heat

4 different ways to lose or gain heat:

• Conduction

• Convection

• Radiation

• Evaporation

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Conduction

• This involves transferring heat directly from one object to another.

• This will not drastically affect the performer unless they are exercising in cold water.

• In this case, they will lose heat about 25 times quicker than in air.

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Convection

• It involves the movement of air molecules.• As air molecules moves over a performer’s

body, heat will be lost as the air carries heat away.

• Wind will increase the movement of air over the body’s surface, and therefore more heat will be lost.

• Hence why fans are used on hot days, or why a cool breeze is pleasant in hot conditions.

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Radiation

• Heat is lost to cooler objects around us, e.g. floors, walls etc.

• This is the main method of heat loss.

• A person’s body composition, size and mass will decide how much heat is lost through radiation.

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Will people with a high % body mass lose more or less than someone with a low % body

mass? Will a tall slim person lose

more or less heat than a short stocky person

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Radiation• Someone with a high % body fat will lose

less, as the body fat acts as an insulator.

• A tall slim person would lose more heat than a short stocky person.

• In hot countries, the sun gives off heat to the body, which will in turn increase the body’s temperature.

• So exercising in hot countries is difficult, as it is difficult for the body to lose excess heat.

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Evaporation

• This is the main method of losing heat, e.g. sweating

• As the sweat evaporates from the skin’s surface, it produces a cooling effect.

• Humid conditions however, reduce the effectiveness of this method

• Sweat will not evaporate in humid conditions, so no heat is lost.

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Exercise in the heat

• As it was highlighted earlier, exercise can increase the metabolic rate.

• It could also increase the core temperature by 1°C every 6 minutes if thermoregulation was not happening.

• If an athlete is exercising in a hot country, then they need to optimise heat loss to avoid hyperthermia.

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Heat loss in hot climates

• Conduction: The body’s blood vessels near the surface dilate to allow more blood to the surface.

• The heat from the blood warms the air and any cooler surfaces than it contacts.

• Conduction works together with convection.

• How?

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Heat loss in hot climates

• Convection:Heat loss is helped if the air around the performer is moving.

• If the air around the athlete is still, then it warms up and insulates the performer, reducing heat loss.

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Heat loss in hot climates

• Evaporation: This is the main way to lose heat.

• As athletes exercise they sweat, this cools the skin.

• If the skin is cooled, then it cools the blood as it is carried through blood vessels close to the skin.

• In order for an athlete to use this method of heat dissipation, they must be well hydrated, with adequate levels of salt and electrolytes in their body.

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Heat loss in hot climates

• In order for any of these three methods to work effectively, athletes rely on the circulatory system.

• The blood is redirected to the surface blood vessels, by dilation.

• In very hot conditions, 15-25% of the cardiac output is directed to the skin.

• Thus heart rate increases even further when exercising in hot climates.

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Heat loss in hot climates

• Heart rate is also raised if the athlete is dehydrated in any way.

• If an athlete is dehydrated, then their plasma level is lower.

• A decrease in the amount of plasma causes a decrease in stroke volume.

• Thus the heart rate must increase to maintain the cardiac output.

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Heat Transfer when exercising

Contracting muscles

Solar Radiation;

Air temperature

Air humidity

Evaporation

(respiratory)

Convection

Conduction

Evaporation

(sweat)

Energy metabolism

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Can you name 3 types of ‘illnesses’caused by

exercising in hot conditions?

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Next week:

We will consider these illnesses.