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Water, electrolytes and temperature regulation; dehydration and hyperhydration sheet
10-mark answer frame

Discuss the role of water and electrolytes in temperature regulation. Add the effects of dehydration and hyperhydration on performance.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Open in two lines. Water makes up about 50-60% of body weight. In exercise it carries fuel and oxygen and removes heat through sweat.
  2. 2 · Draw the heat-loss flow. [Flow: muscle heat → blood → skin vessels widen → sweat → evaporation]
  3. 3 · Water and electrolytes.
    • Water: transport, blood volume, cooling.
    • Sodium and chloride: fluid in blood, lost in sweat.
    • Potassium, calcium, magnesium: nerve and muscle.
  4. 4 · Temperature regulation.
    • Hypothalamus senses core temperature.
    • Vasodilation and sweating; evaporation is the main route.
    • Humidity reduces cooling; acclimatisation in 10-14 days.
  5. 5 · Dehydration and heat illness. Over 2% loss impairs performance; 3-5% cuts strength and skill; heat cramps, exhaustion and stroke.
  6. 6 · Hyperhydration and hyponatraemia. Extra drinking before heat events gives little gain; overdrinking during long events lowers sodium below 135 mmol/L.
  7. 7 · Nutrition link. Urine colour and weight checks; salted nimbu pani, buttermilk or sports drinks in long, sweaty sessions.
  8. 8 · Close in one line. Drink enough to stay within 2% loss, but never so much that weight goes up.

Scoring tip: Give the 2% figure and the 135 mmol/L cut-off; these two numbers anchor the whole answer.