The risks of dehydration


Water accounts for 60% of the weight of a human being. It is the main component of our body. Therefore, dehydration can have a serious effect on the body, because water intervenes in a many of the chemical reactions that make our body function properly. All forms of physical activity produce heat that must be eliminated. This is the reason why we perspire, a phenomenon that incurs the risk of dehydration.

What is a state of dehydration?

Dehydration refers to a lack of water, due to the imbalance between the water we drink and the water we lose.

When we are insufficiently hydrated, the volume of water in the blood decreases and our blood thickens. This means that the heart has to work harder to propel the blood into the vessels.

The level of oxygen and nutrients feeding our muscles is reduced, as is our capacity to eliminate toxins. Under these conditions, our performance drops. A loss of 1% of our body weight in water reduces our physical capacities by 10%.

Dehydration is a source of fatigue and muscular injury.

What are the signs of dehydration?

The main signs of dehydration are:

  • Feeling thirsty,
  • An increased heart rate,
  • A drop in blood pressure,
  • A drop in performance: fatigue, breathlessness, muscular pains.

Chronic dehydration

Chronic dehydration occurs in sportsmen who do not drink enough to meet their needs.

The signs of this condition are fatigue when exercising, feeling tired all the time, a loss of concentration and memory, etc. This fatigue results in a drop in performance, difficulties recovering, cramps, aches and muscular contractions. Your legs frequently feel heavy, especially when you wake up in the morning. Dark coloured urine in the morning is also a sign of dehydration.

This fatigue has a negative effect on the sportsman’s vigilance, which in turn results in a loss of precision. In this way, the loss of performance is accentuated and the risks of injury or falls are increased by the lack of motor coordination.

Drinking less than 1.5 litres of water per day exposes us to the risk of chronic dehydration.

Severe dehydration

Dehydration can stealthily creep up on you, long before you even feel thirsty. You will gradually feel tired when you exercise, your concentration will fail and the coordination of your movements will suffer. Your gestures are less precise and the risk of injury increases.

When exercising, 'one of the first signs of dehydration is feeling thirsty. But it is too late, because you are already dehydrated. You should never wait until you feel thirsty before drinking.

Coping with dehydration due to exercise demands plentiful consumption of liquids that help you to recover. Hypermineralised water is highly recommended.

Situations in which you may be dehydrated


The cold favours the elimination of the heat produced by the human body. In this case, the body reaches its thermal equilibrium more easily, and the sportsman does not feel the need to drink. So the cold can make you feel falsely comfortable and you do not feel the need to drink anything. This can incur the risk of dehydration and all its consequences.


When you exercise, you produce heat. In hot conditions, this heat cannot be properly evacuated, because the exterior environment is almost as hot as your body, or even hotter. This means that your body needs to struggle to eliminate the heat by perspiring even more. You will then lose a lot of water by sweating, sometimes as much as several litres per hour of exercise. Compensating for this loss of water in these situations can become difficult, or even impossible, and the risk of dehydration increases.

The wrong drinks

High-energy drinks have a concentration of particles (sugar, minerals) that is even higher than the concentration in your blood. When you consume this type of drink, the water does not migrate from the drink to your body, but in the other direction first. This incurs the risk of dehydration. Avoid high-energy drinks, even if they can be useful when doing sport under extreme climatic conditions, such as extreme cold.


At altitude, dehydration by perspiration is under-estimated, because you do not realise that you are sweating.

And what's more, the hyperventilation that is essential at altitude to compensate for hypoxia causes dehydration into the air.

Marie Fauchille
Dietician | Nutritionist
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      Your body needs water. For happy and healthy body, you need to compensate for water loss. Before, after and especially during physical exertion, dehydration is any athlete's worst enemy, affecting both the body and sporting performance. That's why staying properly hydrated is essential for all of us. This is why the Aptonia blog is going to publish its first report on the benefits and signs of good hydration for athletes. Firstly, here are 6 tips for staying efficiently hydrated before, during and after exercise.