The importance of fluids to runners

Why fluid is vital to runners

While diet is an important factor in good running performance, the intake of fluids is just as important, if not more so. Staying hydrated and avoiding dehydration is vital both to perform well and for your own well being.

When exercising, the body sweats in order to keep itself cool. Sweat comes from water in the blood, so this needs to be replaced to prevent dehydration. If we run or exercise while dehydrated, the body's temperature can rise quickly which can cause heatstroke, and can in some cases be potentially fatal.

Fluid requirements for runners

As a general rule, it is said the average person needs to drink about 2 liters (67.6oz) of fluid a day. Exercise increases this requirement. Essentially, the more you sweat, the more you need to drink to replace the lost fluid.

Some people naturally sweat heavily, while others seem to barely sweat at all, but even small losses of water can cause fatigue. Training harder, running longer or exercising in hot and humid surroundings can all increase your need for more fluid.

It is estimated that during exercise we lose on average 500 to 1000ml (16.9 to 33.18oz) of fluid an hour. You can work out how much fluid you lose by weighing yourself both before and after exercise. (It is best to take the measurements while naked, so as not to include the sweat absorbed within your clothing.) Each kilogram of weight loss equates to 1 liter of fluid loss. However, you will lose more fluid as urine, so you should drink at least 1.5 liters (50.7oz) of fluid for every kilogram (2.2lb) of weight lost.

The color of urine is also a good indicator of fluid loss. If it's pale — almost straw coloured — and in plentiful supply, then you're well hydrated, but if it’s dark and limited in flow, then you need more fluid.

Facts about fluid loss and exercise

  • a 2 per cent loss of body weight may affect your ability to exercise.
  • a 4 per cent loss of bodyweight can cause exhaustion.
  • If you’re competing, for every 1 per cent drop in body weight there’s about a 5 per cent drop in performance.

If you exercise without replacing fluid, you will become increasingly dehydrated. Your body will find it increasingly difficult to keep cool, your temperature will rise, and you will feel lightheaded and nauseous and ultimately, get fatigue or heatstroke. The only way to prevent deydration is to be well hydrated before you exercise and keep topping up your levels during the activity.

Drinking schedule for running

To succeed with your drinking strategy, you need to get into the habit of drinking during your training, so that your body can gradually adapt to increased fluid intakes. In a race, it is highly unlikely that you will drink too much fluid — not drinking enough is usually the problem.

Most of the time you can probably get away with just consuming plain water, but this may become a problem when you’re sweating very heavily for a prolonged period of time. In these circumstances, an isotonic sports drink containing sodium would be a better option.

Before a run

Always start every running session well hydrated. Aim to drink 300 to 500ml (10.15 to 16.9oz) of fluid around 15 to 20 minutes prior to your session. During exercise, aim to drink 150 to 250ml (5.07o to 8.45oz) every 15 minutes to offset fluid losses — drinking smaller volumes more frequently minimizes stomach discomfort. As a rule, the more you sweat, the more you'll need to drink.

After running exercise

How much fluid you need to drink after your run will depend on how much you have lost, but try to drink at least 500ml (16.9oz). As a rule try to drink 1.5 liters (50.7oz) of fluid for every kilogram (2.2lb) of weight lost during exercise, or keep drinking until your urine is light-coloured. You will get used to what color is usual when you are well hydrated.

Which fluid for runners?

Which fluid you opt for depends on how hard you exercise, and for how long. If you're exercising at a low-to-moderate intensity for less than an hour, then water will be sufficient. If you find it difficult to drink large quantities of plain water, try adding some juice, which will also provide you with some carbohydrates to help restock glycogen stores.

Sports drinks for runners

If your session involves continuous exercise for over an hour, then a sports drink would probably be a better option than just water. Sports drinks help maintain better fluid levels, plus the added carbohydrates provide vital glucose. Most sports drinks are 5 to 8 per cent carbohydrate, which makes them 'isotonic' — a similar concentration to blood — and, therefore, quickly absorbed.

A sports drinks has the added benefit of containing sodium which replaces that lost through sweating. This added sodium is of use particularly if you're someone whose sweat tends to be salty and leaves white marks on your clothes. The sodium has the added benefit of encouraging you to drink more.

Alcohol and running

Although alcohol in moderation is fine, it should not be consumed prior to exercise as this has a detrimental effect on co-ordination skills and performance, and increases the risk of injury. You also need to rehydrate properly after a run before drinking alcohol as alcohol causes dehydration and slows recovery from an injury.

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