Hydration both when exercising, and not exercising, is important. The human body can go weeks without food but only days without water.  We need fluid for many bodily functions including regulating body temperature, moving waste products and nutrients through the body. Throughout the day we are always losing fluid in ways we cannot really measure such as through breathing, small amounts through the skin and also our urine. We don’t need to be surgically attached to a water bottle day and night, but we all need to be more aware of how much we are drinking.

Fluid Performance

In simple terms, to remain hydrated during light activity to marathon training, you need to drink enough fluids to match what you are losing. It is hard to advise a generic daily intake, though many may hear a general estimation of having 6-8 cups of water a day as a starting point. How much fluid we need though is governed by so many factors such as environment, length and intensity of exercise, metabolic rate and even genetics. Training for a marathon, your fluid needs will be higher than those that don’t exercise. On the days you train, you will need more fluid than on the days you don’t.

Day to day hydration basics

One really clear, straight forward indicator to show us if we are hydrated enough or not is the simple colour of out wee. When I go to the loo and it is clear, I feel a smug sense of achievement. The reality is, most of us can’t maintain that all the time. There are certainly external factors that will determine how much fluid we require, such as our environment or personal factors related to body size, the amount we exercise or how much we naturally sweat. You need to make sure you are drinking enough to keep your fluid balance, and writing it down or tracking it on an app is worthwhile.

Let’s keep it simple, and discuss the day to day. Keep an eye on the colour of your urine. Is it relatively clear or dark? Simply by monitoring this you know you need to drink more or you are hydrating well. When you wake up have a glass of water before your breakfast. Make sure you have a drink at each meal and carry a water bottle with you when you go out so you always have fluid with you. If you are training that day, when you get back from your session drink 250 – 500mls of water depending on session effort.  Continue to drink little and often until your urine is straw coloured. This indicates good hydration. Good news as well, teas and coffee in moderation also count towards your daily fluid requirements. They do not dehydrate as common thought says, so you can drink them guilt free, as long as you keep out the sugar!

How hydration affects performance

As during the day, how much fluid we need during our long runs can vary hugely between individuals.

The American College of Science and Medicine’s main message is that the goal of drinking during exercise is to prevent excessive dehydration and excessive changes in electrolyte balance to avoid decreased performance.  You can do this by listening to your body and drinking to thirst, or by estimating sweat rate so you can gauge the exact amount of fluid lost and therefore have know how much fluid to drink to match your losses during exercise. It must be noted though, sweat rate can vary from day-to-day and if you are serious about determining your fluid requirements, you will need to estimate your sweat rate under different conditions and exercise intensities (see end of blog on calculations). Methods include tracking pre and post-body mass or simply checking urine colour.

Water or Sports Drinks?

Studies have shown that flavoured drinks that contain carbohydrate and sodium enhance intake and fluid absorption. This makes sports drinks ideal. Sodium should always be ingested when large salt losses occur, e.g. those with a high sweat rate, exercise over 2 hours, or very “salty” sweat. Water is still fine, but it won’t stimulate fluid intake in the same way and therefore a more planned approach to drinking may benefit to ensure consumption matches requirements.

Top Tips

  • Fluid requirements are highly individual.
  • Drink when you get up and regularly during the day.  
  • Tea and coffee also count!
  • Continue to drink little and often to maintain hydration
  • If you stay hydrated during the day, you will start your exercise hydrated
  • Rehydrate after exercise to replace fluid lost through sweat during exercise

During Exercise

  • DO NOT drink at rates great than sweat loss.
  • Drinking during exercise is not always necessary, but if you are doing a long run or it is particularly hot, sweat rate will be increased, therefore, taking on fluids during activity will help prevent dehydration and symptoms related to it.
  • For longer duration (over 1hr) sports drinks are ideal as they not only hydrate well due to added electrolytes, but they also provide carbohydrate
  • Sodium should be included in fluids that are lasting longer than 1-2 hours where sweat loss has been high.

Race day

  • Start the race hydrated, having little and often during the morning (300-600ml) In endurance races, drink early and taking ‘little and often’ is better than large doses
  • Do not over drink, weight gain after exercise shows an increased risk for hyponatremia
  • If it is hotter than you are used to on race day, be prepared to slow your pace, as drinking more fluid won’t necessarily cool you down
  • After the race you need to drink 150 % of fluid lost (if 1kg weight is lost, you need to drink 1.5 litres) over the next one to two hours and then little and often through the remainder of the day.

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