The Importance of Fluid Intake In Long Distance Running

The Importance of Fluid Intake In Long Distance Running

The Importance of Fluid Intake In Long Distance Running

Written By: Alex Cook
Charlotte Purdue

A good performance in distance running is heavily influenced by fluid intake and taking simple steps to get your intake right could make all the difference to the outcome of your race. We have teamed up with sports dietitian and Salomon ambassador, Alex Cook to discuss all there is to know about fluid intake in long distance running.

Why it’s important

Water makes up over half of our bodyweight and we simply cannot survive without it. It is used for many essential processes; controlling temperature, removing waste products and transporting nutrients and oxygen around the body. Regular ingestion of fluids is not only vital for normal functioning of the body, but it is also vital for optimal sports performance.

Performance & Dehydration

During prolonged exercise athletes are at risk of dehydration. Exercise produces heat and as a result our bodies lose large amounts of water and electrolytes through sweat to cool down. Dehydration results in an increased heart rate, increased perceived exertion, stomach upset and loss of coordination and the more dehydrated you become, the more the effects are pronounced. When an individual is dehydrated by as little as two per cent of their bodyweight, performance is impaired.

In contrast, having too much fluid can be equally as damaging, affecting performance through minor irritations such as stomach discomfort. Some athletes may believe that “more is better” due to the focus we place on remaining hydrated during exercise, but this can have damaging effects and slower runners that are out for longer tend to be at higher risk. So how can we ensure we achieve this fine line between too much fluid or too little?


In order to avoid dehydration, an athlete needs to drink sufficient fluid to match their sweat loss. It is impossible to recommend a generic fluid replacement plan as the amount of sweat lost is highly individual, being governed by various factors such as environment, length and intensity of exercise, metabolic rate and even genetics. As such, the amount of water needed to remain in fluid balance is different for every athlete and situation. For example, Kenyan endurance runners are renowned for taking on little fluid when training. A study by Fudge et al (2008) found that although Kenyan athletes took on little fluid even during demanding training sessions, they managed to remain well hydrated, showing that one hat does not fit all.

The American College of Sports Medicine’s main message is that the goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance. You can do this by listening to your body and drinking to thirst or by estimating sweat rate during exercise. This way you can gauge the amount of fluid lost and be guided on how much you need to drink to match your losses. 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.

How to Calculate Sweat Rate

  1. Record your pre-training weight (kg)
  2. Record your post-training weight (kg)
  3. Run for 30-60min without drinking fluid
  4. Subtract post-run weight from pre-training weight and multiply by 1000 (convert to grams)
  5. The amount you lost in grams is equal to that lost in fluid
  6. If you did a 30min session, multiply that by two to get your ml per hour figure. This is the amount you should aim to drink in subsequent runs (remembering this will change with such things as running intensity and heat

Water or Sports Drinks?

Studies have shown that sports drinks that contain carbohydrates (6-8%) and sodium enhance fluid intake and absorption. This makes sports drinks ideal. Sodium should always be ingested when large salt losses occur, for example; those with a high sweat rate, when exercising for longer than 2 hours or when excreting very “salty” sweat. Water is still fine otherwise, but it won’t stimulate fluid intake in the same way and therefore a more planned approach to drinking may be required to ensure consumption matches requirements.

If you want to learn how to make your own sports drink, check out this article.

The key message is to be aware, but not obsessed. Think about your own hydration strategy and don’t copy the runner in front of you, everyone is different! Check out our entire hydration range here.

Top tips

  • Think about how long you are going to be running for as oppose to the distance. If you are going to be running for longer than 90 mins you will need to consider hydration
  • Start the race hydrated, having little and often during the morning (300-600ml)
  • Try and match fluid intake with weight loss (just below and definitely not over). You can work out your sweat rate for more prescriptive hydration or you can drink to thirst (the later is more appropriate if you run at a slower pace)
  • Drink early in the race and taking ‘little and often’ is better than large doses
  • Do not over drink, weight gain during a marathon 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

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