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The importance of good hydration for athletes

December 29, 2021 5 min read

The importance of good hydration for athletes

This article is an automatic translation from our Original French blog. This text may contain translation errors. Thank you for your understanding.

Staying hydrated seems to make sense. All people drink and consume water-containing foods on a daily basis that can hydrate them. However, staying well hydrated is not as simple as you might think. A study published in the journal Nutrients, and conducted on 573 adults over 8 days, found the following:

- Only 60% were euhydrated, i.e. they did not drink too much or too little water.

- 20% were hyperhydrated, i.e. they had consumed too much water.

- 20% were dehydrated, i.e. they had not consumed enough water.

When we know that water consumption has a major influence on the composition of urine, from its smell and colour to its sodium and potassium concentration, we can imagine how poor hydration in sportsmen and women translates into a drop in performance.

Although this is a logical consequence in the minds of all athletes, especially endurance athletes, their knowledge of proper drinking is limited. We will therefore explain how to drink enough to be hydrated during exercise. First of all, let's define hydration and the term osmolality.

What is hydration and how does it work?

Hydration is simply defined as "the introduction of water into the body". However, this need for hydration is induced by multiple causes of dehydration, which are:

- Urine.

- Excrements.

- Perspiration and other evaporation through the skin.

- Evaporation through breathing.

Water balance is essential for health. This is why dehydration is immediately reflected in the osmolality. To explain this concept simply, let's say that urine osmolality calculates in moles the number of molecules present in it (potassium, sodium, phosphates, urea, creatinine, etc.). It is this variation in physiological osmolality (urine, blood) that will induce the thirst effect and therefore our water consumption.

Regular consumption of water, in balanced proportions, will allow us, in the long term, not to induce diseases, one of the causes of which is chronic dehydration.
In this case :

- Nephrolithiasis (otherwise known as "kidney stones" or "stone disease").

- Chronic kidney disease.

- Hyperglycaemia.

- The development of type II diabetes.

These are the reasons that strongly encourage the daily consumption of water, and on a regular basis. Especially since water consumption ensures the balance of electrolytes in the body, which are the minerals we need to contract our muscles, ensure blood circulation, etc.

Now, what is the correlation between hydration in sportsmen and women and their physical performance?

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The importance of hydration in physical performance

Poor hydration during physical activity has consequences that all sportsmen and women have already experienced, especially endurance sports. Certainly not everyone has realised that these effects are not inherent to a lack of training, but rather to dehydration. These symptoms include:

- Muscle cramps.

- Decreased physical capacity.

- Decreased cognitive abilities.

- Difficulties with thermoregulation.

For those who train for long-distance races (half-marathon, marathon, ultra-trail), it is not uncommon for your failures to be primarily related to poor hydration. This is particularly the case with regard to the appearance of muscle cramps.

Dehydration, which occurs as soon as a water loss of 1 to 2% of the body mass appears, leads to difficulties in thermoregulation. An increase in internal heat due to dehydration leads to a reduction in perspiration and a shift of blood to the skin, which results in a drop in central venous pressure. Thus, the heart is no longer able to regulate both metabolism and thermoregulation at the same time.

The question now is how to consume enough water to maintain performance at its maximum physical capacity?

How much water to drink during physical activity

The advice that is generally given is to drink water in three phases: before exercise, during exercise, and after exercise. However, water requirements differ not only from one individual to another, but also from one situation to another, since external environmental factors (temperature, humidity etc.) are crucial.

Water consumption before exercise

It is important to drink plenty of water before exercise so that you do not start your physical activity in a state of dehydration. However, it is totally unnecessary to overhydrate. Studies have shown that hyperhydration has no benefit compared to euhydration.

So how do you drink enough water without it forcing you to urinate during your physical activity or causing abdominal pain? No study will give you definite figures. You need to adjust your water intake to the colour of your urine.

Dehydration can be seen in the dark colour of the urine. If your urine is dark before the competition, drink about a litre of water over a few dozen minutes. You should then start your activity with a good water balance.

Drinking water during exercise

This is a common misconception among amateur runners: the idea that stopping to drink water, or simply slowing down, will waste time. In the short term, yes. In the long term, however, it will not only allow you to finish the race, but perhaps even accelerate at the end by taking advantage of the second wind.

So, again, don't drink huge quantities, unless the heat you're facing requires it. Adapt to the climatic conditions. In a temperate climate, the figures given often suggest drinking 1 to 2 glasses of water every 20 minutes.

Rehydration after exercise: should you give preference to milk?

When it comes to rehydration after exercise, there is no recipe to determine the number of centilitres or litres necessary to restore a good water balance or the best electrolyte levels.

However, water would not be the best drink to achieve euhydration in the long term. In fact, a study has shown that milk has superior virtues, not only to water, but also to energy drinks for athletes. While drinking milk kept the athletes tested hydrated, drinking water or energy drinks only kept them hydrated for the first hour after drinking them.

Therefore, if you are planning a major physical effort, have a bottle of milk with you after your effort, rather than just a bottle of water or some kind of energy drink.

The exceptions: iron men and experienced marathon runners

If your goal is to become an experienced cross-country runner, repetition of your training will allow you to push all the limits we have just described. For example, a top marathon runner is able to withstand a temperature of 40 degrees Celsius, combined with a 5% loss of body water, and still perform at a body temperature of 41 degrees Celsius.

The same applies to Iron Man runners, who lose between 4 and 8% of their body mass, with a water turnover of up to 16 litres, or an average of 1.33 litres per hour. This makes the risks of dehydration and hyperthermia the two main problems for these athletes.

Here the figures are more precise, indicating that a 3% dehydration leads to a 3-5% loss of performance over a running distance of 1500 to 10,000 metres. However, the intensive training of these athletes allows them to manage these situations of intense stress for the body.


In conclusion, hydration is an essential element of performance. You can use all the training techniques possible, but if you don't drink an ideal amount before and during exercise, you won't be able to take advantage of your full physical potential.
Water consumption is not just about sport. Hypohydration can lead to illness in the long term. It is therefore necessary to drink water regularly on a daily basis.
Finally, as you progress in your sport, you will push your body's limits further and further and increase its capacity to cope with dehydration of varying severity.