Water (H2O) is the main constituent of the human body. The body is made up of around 60% water in adults, and even 75% in young children. Our build can have an influence on this level. The leaner a person is, the higher their water content. Depending on our activity, the human body will also consume more or less water. For our health, it's vital that our intake covers our losses. If our body alerts us when we run out, it's often too late. So it's important to anticipate our needs.
In everyday life, water has many properties that help our bodies function. It transports nutrients into the body via the blood, regulates body temperature via sweat, eliminates waste via urine and serves as the basis for the structure of human cells.
On average, we lose two liters of water1 a day. This amount increases with sporting activity. This loss can be as much as two liters of water per hour, depending on the sport and its intensity. Environmental factors also come into play (temperature, humidity, etc.). This high level of water loss needs to be quickly rebalanced to avoid dehydration.
As a general rule, dehydration eventually leads to an excessive drop in blood pressure, headaches and cramps, and even loss of consciousness, which can lead to death in the event of prolonged deprivation (after 3 days, the risk of after-effects is very high).
There is a link between the percentage of water lost and performance. In fact, a drop in overall performance has been observed for low water losses (from 2% of body weight lost in water2). In the event of a water shortage, our body will prioritize the functioning of the general system over that of the muscular system.
It will therefore prefer to maintain body temperature, for example. That's why you'll be sweating during your effort. The frequency and composition of your hydration are key factors in limiting injury and optimizing your performance.
Hydration in the days leading up to sporting activity is essential. Drinking mineral water will rehydrate you, while providing you with minerals. Mineral water provides calcium, magnesium and/or potassium to make up for mineral loss due to exertion.
For a short effort, mineral water is sufficient. However, it's a good idea to drink a sweetened water afterwards to replenish your energy levels. If you're not sure what to mix, special sports drinks are available. special sports drinks are available.3.
Food is also a major ally when it comes to hydration. Many foods are over 90% water: strawberries, tomatoes, radishes, cucumbers...
There is a technique for determining your water requirements: weigh yourself before and after an event, taking into account the weight of water drunk during exercise4. It is also advisable to ingest water in small quantities throughout the exercise.
1: Beware of the well-known phrase "1.5 liters of water a day". This may be sufficient for a balanced diet and moderate exercise. However, you need to drink regularly, and especially when you're thirsty, even if this exceeds the volume recommended above.
2: Murray B., "Hydration and physical performance", October 2007
3: Nicolas AUBINEAU, "Boisson énergétique - Comparatif 2018" (in French)
4: Union française des œuvres laïques d'éducation physique, "L'hydratation du sportif" from "Vidal, le guide sport et santé", 2005