Staying Hydrated before, during and after exercise

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Maintaining adequate hydration is essential for the performance of an athlete. Water balance on a daily basis depends on the net difference between water gain and water loss. Dehydration is the excessive loss of body water which can decrease performance during exercise and have negative effects on physical and mental function. Therefore, sufficient fluid intake before, during and after exercise is important for health and optimal performance. There are several ways to estimate our hydration status.

How do I know whether I am dehydrated after exercise?

Dehydration can be detected by frequent monitoring of body weight. Specifically, one way to check your hydration status is to weigh yourself before and after exercise. This can be used to estimate your sweat loss and your fluid requirements. Below you can find the percentage of change in body weight before and after exercise and the state of dehydration it indicates:

% Body Weight Change

  • Well Hydrated
                        -1 to +1%
  • Minimal Dehydration          -1 to -3%
  • Significant Dehydration     -3 to -5%
  • Serious Dehydration            > -5%

These fluid losses need to be replaced, as a body water deficit of greater than 2% of body weight marks the level of dehydration that can adversely affect performance.

A good rule to manage the dehydration is to consume 1.5 litres of fluid per kg difference between your weight before and your weight after exercise. For example, if an athlete weighs 70 kg before exercise and then weight drops to 69.5 kg after exercise; they should consume 0.75 litres of water / liquids.


Is there any other way with which I can estimate the hydration levels of my body?

There are many other ways which can help you estimate your hydration levels. For example:

  • The monitoring of your urination habits (frequency and amount)
  • The monitoring of your urine colour (the darker the urine the more dehydrated we are).


Can I drink anything else other than water while exercising?

Apart from water, you can also consume fluids such as fruit juices, energy drinks and sports drinks. For athletes exercising for more than one hour, such as endurance cyclists and marathon runners it is also recommended to consume isotonic fluids during exercise.

Isotonic drinks contain similar concentrations of salt and sugar as in the human body, thus they are absorbed into the body more rapidly than water, as well as providing energy. A simple recipe is isotonic drink 200ml squash (not sugar-free or low calorie), 750-800ml water and a large pinch of salt (1/4 tsp). This will produce an isotonic drink containing 6-7% carbohydrate solution, depending on the type of squash used.

It is important to highlight that the fluids must be consumed wisely. Excessive consumption of fluids will lead to frequent urination and as such it can affect your performance. Moreover, you should not consume too much water, especially in long races because of the risk of hyponatremia (low sodium in the blood). Hyponatremia can be prevented by use of isotonic drinks.


What else should I have in my mind about maintaining a good hydration status?

Two important rules that would be good to keep in mind are:

  • Do not wait to feel thirsty to drink. Take a few sips every 10 to 20 minutes during exercise to stay properly hydrated.
  • Following the completion of your exercise session, replenish your fluid loss and avoid caffeine (e.g. tea, coffee) or alcohol as they are diuretics and can interfere in your hydration plan.




American College of Sports Medicine. 2011. Selecting and Effectively Using Hydration for Fitness. [online] Available from:

Casa, D.J., Clarkson, P.M. and Roberts, W.O., 2005. American College of Sports Medicine Roundtable on Hydration and Physical Activity: Consensus Statements. Current Sports Medicine Reports, Vol. 4, no. 115–127, [online] Available from:




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