Nutrition

Why is Hydration Important for Exercise?

Around 70% of our body is made up of water and it is vital for every chemical reaction in the body. We need around 2-3 litres a day to transport nutrients, help with cellular enzyme activity and digestion of food, to carry out waste and toxins, and also to support brain function for mood, energy and concentration.

We lose water and also body salts (largely sodium and chloride) through urine, but also when it evaporates as sweat and the in the air we breathe. More fluids are lost during exercise, particularly in warmer weather, but a loss of only 1-2% of our body weight can impair performance by around 10-20%.

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HOW TO STAY HYDRATED

Some of the water we need will be extracted from our food, but day to day, we should be aiming to drink around 1.5 - 2 litres (c 6 large glasses) to replenish our stores.

This amount should be increased during exercise to prevent dehydration, and sports drinks which also contain carbohydrate (CHO) in the form of glucose, can also be beneficial to help replenish glycogen stores.

Everyone loses fluids at different rates, and depending on their level of exertion, but as a general guide, always start any exercise session well-hydrated, then follow these guidelines according to the duration of your session:

• Exercise under 30 minutes:
  No need to drink whilst exercising (unless it's very warm), but re-hydrate with water after the session.

• Exercise from 30-60 minutes:
  As above, then re-hydrate post-training with a drink containing both water and CHO.

• Exercise 1-3 hrs:
  Take a sports drink with you which combines water and CHO. Sip regularly throughout the session - aim for 30-60g CHO per hour. Continue to use the same drink post training.

• Exercise 3hrs +:

• Choose a sports drink which combines water, CHO and some sodium/salts. Sip regularly taking on 30-60g CHO per hour and continue to drink post training.

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CHECKING HYDRATION LEVELS:

There are two effective ways to check hydration levels when exercising. Weigh yourself both pre and post a session to see how much weight has reduced. A 1kg weight loss equates to around 1 litre of fluid and you should aim to restore levels to your original weight post-training. You can also check your urine colour. The darker it is, the more dehydrated you are (although if you are taking single nutrient supplements these can affect urine colour; e.g. B Vitamins can turn urine fluorescent yellow.)

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TYPES OF SPORTS DRINKS

Commercial sports drinks are designed to offer you a combination of the fluids and salts you lose during exercise, and they come with a variety of descriptions.

• Hypotonic
  Contain a small amount of CHO (under 4%). This is lower than your blood plasma concentration and so they are relatively easy to absorb and digest.

• Isotonic
  Contain 4-8% CHO and also some salts, which is similar to the concentration of the blood plasma, so are a better choice for replacing fluids rapidly during prolonged exercise.

• Hypertonic
  Include a higher concentration of CHO at over 8%, but do not include salts, and are sometimes used for refuelling glycogen stores post exercise. They can also be used during endurance events, but should be combined with isotonic drinks to ensure salts are also replenished.

Sports drinks can easily be made at home and are much cheaper than buying commercial brands. An isotonic drink you can try could include:

• 200ml of fruit squash

• 800ml water

• A pinch of salt

Mix together and cool in the fridge

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TIPS FOR HYDRATING

• Don't allow yourself to become thirsty. If you are thirsty you are already dehydrated.

• Check your urine colour to monitor our levels of hydration.

• Sip small amounts frequently and practice drinking as part of your training (particularly if you are in training for a big event).

• Try sports drinks before the event to ensure they agree with you. Most endurance events will tell you which ones they use.

• Don't over-drink.   This can lead to hyponatremia, whereby plasma sodium levels are depleted to dangerous levels, resulting in confusion, lack of co-ordination and in some cases this can be fatal.

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Keen to learn more about fuelling for performance and adventures? Then check out our Nutrition category for more handy tips, advice and recipes.