During exercise, our bodies sweat to keep the temperature from rising too much. As a result, we lose water through our skin and unless this is replenished, dehydration can arise.
Dehydration is defined as a body fluid deficit of more than 2 % of bodyweight (e.g. a 2 kg loss in a person weighing 100kg, or a 1 kg loss in a person weighing 50kg). When this happens, blood volume decreases leading to a drop in blood pressure and blood flow, making exercise much harder. Performance (both physical and mental) is impacted, and fatigue will set in faster. It is therefore essential that athletes strive to avoid a loss of body fluid of more than 2%.
Signs and symptoms of dehydration in athletes include:
- Dark-coloured urine and lower urine output
- Poor mental focus
- Confusion and unconsciousness in severe dehydration
Conditions/events that increase the risk of dehydration include:
- Warm weather and/or high humidity
- Exercising at higher altitudes
- Training at high intensities
- Concomitant diarrhoea and/or gastroenteritis
Electrolyte supplements or sports drinks can be used during training or competitions of long duration to help prevent dehydration and electrolyte imbalances. These contain glucose and salt that facilitate rehydration and replenish salts lost through sweat. If such drinks or supplements are not available, salty carbohydrate foods such as cereal or salted crackers can be consumed alongside water.
How much should you drink after training?
To fully rehydrate after training, you need to drink about 125 to 150mL for every 100g of body weight lost. This is because the body will keep losing fluids (sweat) even after exercise has stopped. Therefore, if you weigh yourself before and after exercise, and you find that you have lost 1kg, you should aim to drink between 1.25 to 1.5L of fluid to fully rehydrate.