Water, electrolytes and temperature regulation; dehydration and hyperhydration
Working muscles make heat, which the body loses mainly by evaporating sweat. Losing more than 2% of body weight as sweat hurts performance; drinking far too much causes hyponatraemia.
Roles of water and electrolytes in exercise
| Item | Role |
|---|---|
| Water | Carries glucose and oxygen to muscle and removes CO2 and lactate; keeps up blood volume for the heart; cools the body through sweat; cushions joints |
| Sodium | Main mineral outside cells; holds water in the blood; drives thirst; the main mineral lost in sweat |
| Chloride | Travels with sodium; also lost in sweat |
| Potassium | Main mineral inside cells; nerve and muscle function; small sweat loss |
| Calcium and magnesium | Muscle contraction and relaxation |
How the body controls temperature during exercise
- 1Working muscles release heat: about 75-80% of the energy they use.
- 2★Core temperature rises; the hypothalamus senses it.
- 3Skin blood vessels widen (vasodilation) and carry heat to the skin.
- 4★Sweat glands release sweat; evaporation removes heat (about 580 kcal for each litre that evaporates).
- 5Radiation, conduction and convection help only when the air is cooler than the skin.
- 6In humid coastal cities such as Chennai, Mumbai and Kolkata, sweat drips off instead of evaporating, so cooling is poor.
- 7Heat acclimatisation over about 10-14 days: earlier and more sweating, more dilute sweat, bigger plasma volume, lower heart rate.
★ one-way, controls the pace
Effects of dehydration on performance
| Fluid lost (% of body weight) | Typical effects |
|---|---|
| About 1% | Thirst; body temperature starts to rise faster |
| Over 2% | Aerobic performance, concentration and decision-making fall (ACSM) |
| About 3-5% | Endurance falls further; skill drops; strength and power fall a little; headache, cramps, nausea; risk of heat exhaustion |
| Higher losses | Risk of heat stroke and collapse; can be life-threatening |
Heat illness
| Type | Signs | First aid |
|---|---|---|
| Heat cramps | Painful muscle cramps; heavy, salty sweating | Stop, stretch, drink fluid with salt |
| Heat exhaustion | Tiredness, dizziness, headache, nausea, pale clammy skin, fast pulse | Shade, lie down with legs raised, cool the body, give fluids with salt |
| Heat stroke | Core temperature above about 40 °C with confusion or collapse; a medical emergency | Call for help; cool at once (cold-water immersion or ice towels); then hospital |
Hyperhydration vs hyponatraemia
Indian summers make hydration planning essential: a fast bowler in Chennai or a kabaddi player in a hall without air-conditioning can lose more than a litre an hour. Teach athletes to check urine colour and body weight, and to use salted nimbu pani, buttermilk or a sports drink in long, sweaty sessions.
2 marks: “What is exercise-associated hyponatraemia?” Blood sodium below 135 mmol/L during or after exercise, usually from drinking more than sweat losses; causes headache, confusion and seizures.
5 marks: “Explain heat illness in athletes.” Heat cramps, heat exhaustion and heat stroke: signs and first aid for each; prevention by acclimatisation, fluids and timing of training.
10 marks: “Discuss the role of water and electrolytes in temperature regulation and the effects of dehydration and hyperhydration on performance.” Roles of water and electrolytes, steps of temperature control, dehydration effects by % loss, heat illness, hyperhydration and hyponatraemia.
2% rule: lose more than 2% of body weight and performance drops; gain weight during exercise and you drank too much.