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You've seen it; runners carrying big water bottles on a run around the block, runners in events drinking a cup full and more at every water station. Sometimes it can be too much and sometimes not enough. Without drinking the right amount your whole running experience can be very different than it should be, but you can also go too far. Here we walk you through some of the do's and don'ts.

There are four phases we need to look at; normal everyday life, pre-training, training and during your event, if you're doing one.

Everyday life

First of all, we know that water is a crucial element for life, representing around 45% to 70% of our body. Like oil in a car, water in the body (and fluid in general) is needed for different functions such as transporting nutrients and compounds in the blood, removing waste products through urine, regulating body temperature, allowing our muscles to contract and joints to move. In fact, water acts as a lubricant and shock absorber in your joints. For athletes dehydration can lead to reduced endurance, strength and heat-related illness. There is evidence reporting that with just 1.5% of dehydration our concentration and mental ability can be impaired. Ironically, we don't feel thirsty until we are 1-2% dehydrated - which means that we need to drink before we realise it otherwise we are likely to end up training being already dehydrated.

You should be having 6-8 glasses of fluid a day whether you are training or not. This should be mostly water, low-fat milk, soy milk, no added sugar squash, or herbal teas.

Why? A humble glass of H2O may not be the most popular pre-workout tipple for Americans, but it's certainly the most essential. A study published in the journal Sports Medicine found dehydration "consistently attenuates strength (by 2%), power (by 3%) and high-intensity endurance (by 10%)."

Before Training

As a rule of thumb, drink a 250ml glass of water 30 minutes before you hit the gym, or starting your training run, to ensure your muscles are firing on all cylinders. Then follow that up with 500ml within 30 minutes of finishing. Deciding how much to sip mid-session is more subjective.

After 90 minutes of moderate exercise, water is no longer enough. At this point, your glycogen stores are low and it's time to start sipping electrolyte-rich sports drinks. For endurance athletes, managing minerals is exceptionally important and, although the concept of drinking too much water may seem strange, it can be dangerous. Drinking litres of water without replacing electrolytes can cause a condition called hyponatremia, which may lead to seizures, organ failure and even death. Staying hydrated is essential for our performance, mental and physical health. Therefore, it is crucial to start each training session or competition fully hydrated. However, this is not sufficient as we need to drink appropriate fluids even during training and competitions and restore hydration levels as soon as possible afterwards, to replace any fluids and salts lost through sweat. Why salts? Because when we train at high intensity we sweat a lot and, therefore, we need to be sure to have enough salts in our diet to compensate for the losses.

In general, the British Dietetics Associations (BDA) recommends around 2 litres of water per day for men and 1.6 litres per day for women. However, these guidelines do not take into account physical activity and sweat rates, which vary among individuals. Therefore, it is extremely important to create a hydration plan and adopt personalised hydration strategies to avoid dehydration. Studies have shown that, depending on the environment temperature, our body size and exercise intensity we can lose from 1.5L up to 4L during physical activity - all these fluids would need to be replaced.

During training

How much water should I drink while exercising?

There are no exact rules for how much water to drink while exercising, because everyone is different. You need to consider factors including your sweat rate, the heat and humidity in your environment, your clothing, and how long and hard you are exercising.

You may need to stay better hydrated if you have certain medical conditions, such as diabetes, heart disease, and cystic fibrosis. Some medications can act as diuretics, causing the body to lose more fluid. The American Council on Exercise has suggested the following basic guidelines for drinking water before, during, and after exercise:

  • Drink 17 to 20 ounces of water 2 to 3 hours before you start exercising.

  • Drink 8 ounces of water 20 to 30 minutes before you start exercising or during your warm-up.

  • Drink 7 to 10 ounces of water every 10 to 20 minutes during exercise.

  • Drink 8 ounces of water no more than 30 minutes after you exercise.

Athletes may want to measure how much fluid they lose during exercise to get a more specific measurement of how much water to drink (16 to 24 ounces of water for every pound of body weight lost). Dehydration happens when you lose more fluid than you drink. When your body doesn’t have enough water, it can’t work properly. Dehydration can range from mild to severe. Symptoms of dehydration can include the following:

  • Dizziness or lightheaded feeling

  • Nausea or vomiting

  • Muscle cramps

  • Dry mouth

  • Lack of sweating

  • Hard, fast heartbeat

Most people know that exercise and, in particular, training at a high intensity can lead to dehydration and pay attention to drink enough water before, during and after their workout. However, our body contains electrolytes, such as sodium, chloride, bicarbonate or potassium, which are minerals in charge of carrying out chemical reactions in our body and maintaining a steady blood volume. If you drink too much plain water you may end up diluting the body’s electrolytes, causing an electrolyte imbalance called hyponatremia. Therefore, if fluid losses during or after exercise are significant and you notice that you have a salty sweat, it may be necessary to include some electrolytes too.

What to drink solely depends on the type, intensity and duration of physical activity (and your goals). If you train at a low to moderate intensity for less than 1 hour with low sweat losses you only need water. If you train at a higher intensity with sessions lasting longer than 1 hour and great sweat losses you may need an isotonic sports drink or a homemade sports drink.

Event day

You can definitely drink too much water and, if you’re not also taking on adequate electrolytes, you’ll effectively dilute and affect the balance of your body’s fluids (hyponatraemia). This can lead to a feeling of being bloated and nauseous; in extreme it can be fatal. Cases of this have been seen in recent years at big city centre marathons where runners have drunk too much plain water.

Remember, as well as replacing lost fluid, you also have to replace lost electrolytes too. Anyone running for more than four hours should be guided by thirst – avoid drinking huge amounts of water, and use sports drinks that contain sodium.

What is heat illness?

Heat illness can occur when your body is dehydrated and can’t cool itself effectively during exercise in hot or humid weather. There are 3 stages of heat illness:

  • Heat cramps

  • Heat exhaustion

  • Heat Stroke

Symptoms of heat cramps include painful muscle spasms in the legs, stomach, arms, or back. Symptoms of heat exhaustion are more serious. They can include faint or weak feelings, nausea, headache, fast heartbeat, and low blood pressure. The most serious heat-related illness is heatstroke. Symptoms can include high body temperature (higher than 104°F), fast heartbeat, flushed skin, fast breathing, and possibly even confusion or delirium, loss of consciousness, or seizures. You should get emergency medical attention immediately if you experience any of the symptoms of heatstroke. Untreated heat stroke can lead to death.

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