Keeping hydrated for exercise

Expert reviewer, Dr Leon Creaney, Sports & Exercise Medicine Consultant
Next review due March 2021

Whether you’re an elite athlete or a weekend warrior, hydration is key during exercise.

Here are some of our top tips to help guide you on how much you need to drink, and what to drink, before, during and after exercise.

Why is hydration important during exercise?

Around 60% of your body is water and it plays a vital role in every bodily function. You can lose a lot of fluid when you exercise – as much as a litre or two an hour – mainly through sweating and breathing.

If you don’t top this fluid back up, you can get dehydrated. This can affect both your general health and how well you can exercise. You’ll feel tired more quickly if you’re dehydrated, and you won’t be able to control your temperature as well as usual.

Water helps fuel your muscles, so drinking before, during and after exercise will boost your energy levels, and may help to prevent cramp.

Hydration before you exercise

It may not cross your mind, but making sure you’re well hydrated before you exercise is really important, especially in hot conditions.

If you’re dehydrated before you start exercising:

  • your core temperature will rise faster
  • your heart will have to work harder than usual

This will affect your performance and can even lead to heat stroke. Drinking enough will help you get the most out of your exercise session and feel good while you’re doing it.

One quick way to test if you’re hydrated is to check the colour of your urine. 

Image showing hydration level by urine colour 

Top tip

It can take time for fluids to be absorbed into your body. So drink steadily during the day and aim to drink around 500ml of fluid at least four hours before you exercise. In the 10 to 15 minutes before you exercise, top up your fluid levels by drinking about half this amount again.

Hydration during exercise

It’s important to drink water during a workout – take a water bottle with you on a run, for example. Being dehydrated can affect your energy levels. Your muscle cells are almost three-quarters water so if you're short on fluid, you’ll feel the strain. Drinking little and often rather than a lot less often will give you the best chance of hitting your exercise targets.

How much you need to drink will depend on how much you sweat and how long you exercise for. How much you sweat and lose water is influenced by your:

  • size – larger people tend to sweat more than smaller people, and men sweat more than women
  • fitness – fitter people sweat more and earlier in exercise because their bodies are accustomed to needing to cool down
  • environment – you sweat more in hot, humid conditions
  • exercise intensity – you sweat more as you exercise harder

The best way to figure out how much to drink is to respond to what your body tells you. If you feel thirsty, you really need to drink as your body is already showing signs that it needs to take on more fluid. Here’s another way to work out how much fluid you lose while exercising and how much to drink to compensate for it.

The sweat rate calculation
Weigh yourself before exercise (ideally do this first thing in the morning after you go to the toilet).
Weigh yourself after exercise.
Compare the figures.

For every kilogram of body weight you lose, drink up to a litre and a half of fluid.

Top tip

Make sure you always have a bottle of water handy when you exercise so you don’t get dehydrated.

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Hydration after exercise

Once all the hard work is over, no doubt you’ll be ready for something to drink. Not only will this be refreshing, but it will also restore your fluid levels and help your muscles to recover. The sooner you start to replace the fluid, the sooner you’ll recover.

Top tip

Don’t be tempted to reward yourself after exercise with a pint or a glass of wine. Alcohol is a diuretic, which means it removes water from your body by increasing how much urine your kidneys produce.

Do I need to drink sports drinks?

The array of sports drinks on the market can be overwhelming and they can contain lots of added sugar. So it’s hard to know which to choose and if they really offer any benefit.

If you’re doing moderate amounts of exercise, you won’t need them. Simple water is often the best thing to drink during and after a workout. But if you’re doing strenuous training, sports drinks may be useful.

  • If you’re exercising for less than an hour, water is all you need to keep hydrated.
  • If you’re exercising for longer than an hour, sports drinks or even just squash can help you keep going for longer. As well as replacing lost fluid, they contain carbohydrates (sugar) and electrolytes like sodium, potassium and magnesium, which you lose though sweat. These drinks provide fuel and help to keep you hydrated.

Make your own sports drink

To avoid spending lots of money on sports drinks which may contain lots of sugar and additives, try making your own at home. Mix 200ml squash (not a low-sugar variety) with 800ml water and add a large pinch of salt.

If you’re training for an endurance event like a marathon or triathlon, speak to a dietitian for advice that’s personalised for you. For more information, take a look at our guide on nutrition for sports and exercise.

Can you drink too much?

Drinking too much can potentially be harmful as it can cause a rare condition called hyponatraemia. This is when you drink more fluid than you lose through sweating and weeing. The excess water dilutes the salts in your body and your cells swell up, which can cause a number of problems. The amount you have to drink to get hyponatraemia varies hugely from person to person. The symptoms include:

  • feeling confused or disorientated
  • difficulty balancing
  • a headache
  • feeling sick or vomiting
  • feeling bloated

In a worst-case scenario, severe hyponatraemia can lead to a coma, seizures (fits) and even death.

If you have any of the symptoms above while you’re drinking while exercising, seek urgent medical advice.

Top tip

Get to know what your sweat rate is (see our Hydration during exercise section above) and track how much you’re drinking. If you’re using a refillable bottle, make a mental note of how many times you top it up.

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  • Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, March 2018
    Expert reviewer, Dr Leon Creaney, Sports & Exercise Medicine Consultant
    Next review due March 2021