physical exercise: dehydration and sport

Staying hydrated during sport: The interplay between dehydration and sport

Dehydration refers to a state where there is an inadequate amount of fluid in the body. People who participate in endurance sports or long workouts are particularly at risk of becoming dehydrated quickly. A person is considered dehydrated when they have lost more than 2% of their body weight during exercise.1 All levels of dehydration impair physical performance, even mild dehydration. It reduces physical performance by increasing heart rate and reduces mental function and skill level. It also causes the person to have an increased exertion perception (i.e. exercise feels harder than usual and the athlete fatigues earlier).2

How does dehydration occur from vigorous exercise or sport?

Dehydration during physical exercise is common, because voluntary fluid intake is usually less than fluid losses that occur from sweating. Dehydration causes negative effects on the body’s ability to function and these are magnified by increases in heat stress, exercise duration and exercise intensity. Drinking enough fluids during sport helps to minimise the decrease in blood volume and blood flow to muscles that occurs when a person is dehydrated. Staying hydrated also minimises the rise in core body temperature that happens when we exercise.3

What are the signs and symptoms of dehydration during sport?

Symptoms of dehydration during exercise may include:1
  • A dry or sticky mouth
  • Decreased or no urine output
  • Weakness
  • Dizziness
  • Concentrated, dark coloured urine
  • Skin that doesn’t bounce back quickly when pinched

How can I help to prevent dehydration during sport or physical exercise?

In order to prevent dehydration, drink plenty of water before, during and after exercise. This is particularly important in hot weather or during intensive activity. Take a drink bottle with you and try to drink at least every 15 to 20 minutes during your exercise session. Avoid drinks containing caffeine, such as coffee, colas, or tea. These increase urine output and therefore your risk of becoming dehydrated. You should also avoid drinking alcohol for the same reason. Wear one layer of light coloured, lightweight clothing when exercising outdoors and change into dry clothes as soon as possible if they become soaked with sweat. You should also stop exercising if you feel dizzy, light headed or very tired.4

How do I treat the symptoms of dehydration after playing sport?

If you become mildly or moderately dehydrated while exercising, you can usually alleviate the symptoms by doing the following:5
  • Stop exercising and rest.
  • Get out of the sun and lie down in a cool spot.
  • Remove any extra clothes and prop your feet up.
  • Drink an electrolyte sports rehydration drink to replace lost fluids and minerals. You should drink approximately 2 litres of cool liquids over the following 2‐4 hours.
  • Rest for the next 24 hours and continue to drink a lot of fluids. You may start to feel better within a few hours, although it could take as long as 36 hours to replace fluid losses completely.