Hydration & Exercise: Before, During and After working out


Around 60% of our bodies are made up of water and it plays a vital role in every bodily function. During exercise we can lose up to 1L of water per hour, mainly through sweating and breathing.


If we don’t top these fluids back up then we can get dehydrated. Being dehydrated can affect both our general health and how well we can exercise. We’ll feel tired more quickly and wont be able to control our temperature as well as usual.


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





Once the session is over, 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 recover.


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


What about sports drinks?


There is a huge array of sports drinks on the market most claiming additional benefits over water.


If you’re doing moderate amounts of exercise, you probably won’t need them. It’s only if you’re doing a lot of strenuous training that they 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 can help you keep going for longer. As well as replacing lost fluid, they contain carbohydrates (sugar) and electrolytes. Electrolytes are the substances (sodium, potassium, magnesium and chloride) that salts break down into when they dissolve in fluid. If you do take the occasional sports drink only drink it after you start training or after you finish. Also check the sugar level in it. For every 4g of sugar that is equivalent to 1 teaspoon of white sugar (see table here).



Being dehydrated can affect your energy levels. Your muscle cells are almost three-quarters water so if your short on fluids, you’ll feel the strain. Drinking little and often is the best way of hitting your exercise targets.


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

  • genetics – some people sweat more than others

  • size – larger people tend to sweat more than smaller people. And men sweat more than women

  • fitness – fitter people sweat more 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. Simply, if you feel thirsty, drink. However ideally you should drink before you feel thirsty. There is a more accurate way to work out how much fluid you lose while exercising and how much to drink to compensate for it.


Sweat Rate Calculation (SWC) = weight before exercising – weight after exercising


The difference in weight (SWC) is due to your loss in fluid. For every kilogram of weight loss that is equivalent to one litre of fluid. However, this needs to be over compensated, so:


For every kilogram of body weight lost during exercise, drink up to one and a half litres.



It may not have crossed your mind but making sure you’re well hydrated before you exercise is really important, especially when it’s hot.


If you’re dehydrated before you even 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.


So, before you exercise, drink steadily during the day and ideally drink around 500ml of fluid at least four hours before you start. Then 10 to 15 minutes before you exercise, top up your fluid levels by drinking about 250ml. So try and arrive a little early for your session, relax and drink before warming up.