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2010 hot conditions

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  • Use of hot and cold cups to feel the transfer of heat
  • Put your hand above hot water
  • Leave the cup of hot or cold water on a table for a few minutes and feel the table.
  • It rained, how does the road dry? the water evaporates!
  • Conduction ; The athlete’s skin goes a rosy red colour.
  • Transcript

    • 1. Heat transfers and hot conditions P1 BND Sport Yr 2
    • 2. 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.
    • 3. Task: List different ways that heat can be transferred.
    • 4. The transfer of heat
      • 4 different ways to lose or gain heat:
      • Conduction
      • Convection
      • Radiation
      • Evaporation
    • 5. 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.
    • 6. 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.
    • 7. 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.
    • 8. 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
    • 9. 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.
    • 10. 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.
    • 11. 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.
    • 12. 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?
    • 13. 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.
    • 14. 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.
    • 15. 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.
    • 16. 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.
    • 17. Heat Transfer when exercising Contracting muscles Solar Radiation; Air temperature Air humidity Evaporation (respiratory) Convection Conduction Evaporation (sweat) Energy metabolism
    • 18. Can you name 3 types of ‘illnesses’ caused by exercising in hot conditions?
    • 19. Next week:
      • We will consider these illnesses.