Exercise is thirsty work. When your swimmers exercise they lose water not only through sweat, but also through water vapour from the air they breathe out. The harder and longer they exercise the more fluid they will lose. It is difficult for swimmers to appreciate how much fluid they are losing through sweat as they are already in water! However, an excessive loss of fluid - dehydration - impairs performance and has health implications.

When a swimmer becomes dehydrated, their blood thickens and so the heart has to work harder to pump blood around the body. It becomes much harder to do the same level and intensity of exercise. Also the more dehydrated they become, the harder it is to sweat, and so their body temperature starts to rise.

Swimmers can limit their fluid loss by following a few guidelines:

                Ensure they have been drinking regularly prior to the session - prevention is better that cure. If they are training in the evening, then they need to ensure that they have been drinking regularly all day. If they are training first thing in the morning, then they should have plenty to drink before they set out.

                Drink during exercise. All swimmers should be encouraged to drink during training sessions, even beginners who are doing very low level workouts. This establishes good habits which will stay with them through their swimming career.
Swimmers should be encouraged to drink as much as they comfortably can. Little sips taken regularly may help swimmers to achieve this.

               After training, maintain hydration. It is virtually impossible to drink too much.


What to drink?

There are a number of different commercial products on the market which are aimed at athletes, each claiming to be the best for top level performance. The type of drink to chose depends on the level and intensity of the exercise, the temperature and the rate at which the individual sweats. The following table gives a working guide:


Exercise conditions

Sports drink

Exercise lasting less than 30 minutes


Low to moderate intensity exercise lasting up to 1 hour

Water or a fluid replacing drink (hypotonic or isotonic)

Strenuous exercise lasting 1-2 hours

Water or a fluid replacing drink (hypotonic or isotonic)

Strenuous exercise lasting more than 90 minutes under cool conditions

Hypotonic or isotonic sports drink, or a carbohydrate drink


                A hypotonic drink contains fewer particles per 100ml than the body's own fluids. As it is more dilute it is absorbed faster than plain water. Typically an hypotonic drink contains less than 4g of sugar per 100ml.

                An isotonic drink has the same number of particles per 100ml and is therefore absorbed at the same rate as plain water. Most commercial isotonic drinks contain between 4g and 8g of sugar per 100ml. In theory these drinks provide an ideal compromise between hydration and refuelling with carbohydrates.

                A carbohydrate drink (hypertonic) contains more particles per 100ml than the body's fluids, and is therefore not good for rehydrating during training. It is best used after training to refuel the muscles.


hypotonic drinks

isotonic drinks


Diluted squash (1 part squash to 6 parts water) Diluted fruit juice (1:3)

Diluted squash (1:4)

Diluted fruit juice (1:1)


Try and ensure that your swimmers do not drink too many fizzy drinks during the day as these are diuretics and can promote fluid toss rather than aid rehydration. They are also not good for their teeth!


The urine test

To check how hydrated your swimmers are, get them to do the urine test(!). When they visit the toilet, get them to look at the colour and nature of their urine. If it is pale and copious, then they are well hydrated and should keep up the good work. If it is dark yellow, and there is not a lot of it, then they are becoming dehydrated and should ensure that they take plenty of fluids. Remind the swimmers that thirst is a very poor indicator of hydration - when you feel thirsty you are already becoming dehydrated.