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Diet and Nutrition

Hydration before, during and after exercise

  • 3 things to know
  • Paper 2

Overview

Dehydration and thermoregulation, fluid loss and worked calculations, hydrating before, during and after exercise, isotonic, hypotonic and hypertonic drinks, and hyponatraemia.

What you need to know

Answer each one before you reveal it.

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Key term

When does an isotonic drink suit a performer, and when is a hypotonic drink more useful?

Numbers

A tennis player has a mass of 70.0 kg before a match and 68.6 kg after it. What percentage of body mass has been lost?

Key term

Why is water essential during exercise?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why is water essential during exercise?

    Model answer

    Water is the main component of blood plasma and of sweat. Sweating removes heat, so water is vital for regulating body temperature.

  2. 2

    How does dehydration affect the cardiovascular system during exercise?

    Model answer

    Dehydration reduces plasma volume, so the blood becomes more viscous. Stroke volume falls and heart rate rises to maintain cardiac output.

  3. 3

    Explain how dehydration affects thermoregulation.

    Model answer

    Less fluid is available for sweating, so the body loses heat less effectively. Core temperature rises and the risk of heat exhaustion increases.

  4. 4

    What level of fluid loss begins to impair performance?

    Model answer

    A loss of about 2% of body mass through sweating can noticeably reduce performance. Larger losses cause greater impairment and raise the risk of heat illness.

  5. 5

    A tennis player has a mass of 70.0 kg before a match and 68.6 kg after it. What percentage of body mass has been lost?

    Model answer

    The player has lost 2% of body mass. The loss is 70.0 − 68.6 = 1.4 kg. Percentage lost = 1.4 ÷ 70.0 × 100 = 2%.

  6. 6

    A footballer loses 1.2 kg of body mass during a match. Using a guideline of 1.5 litres of fluid per kilogram lost, how much should be drunk afterwards?

    Model answer

    The footballer should drink about 1.8 litres of fluid. Fluid needed = 1.2 kg × 1.5 L per kg = 1.8 L.

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