Tips & info

Hydration tips for trail running

Hydratation course

Understand Dehydration

1% dehydration = 10% loss of performance.

And yes it's no joke. You already know that drinking is important. And on a big outing or competition at over 25°C, you very quickly lose 1 to 1.5 liters of body water per hour. At this rate, you quickly end up feeling nauseous, feeling drunk or even downright feeling unwell.

Dehydration is "THE" element not to be neglected to perform and not get injured. Dehydrated, concentration, nerve and muscle tone decline, and every rock you step on can crush your ankle and ruin your run. In addition, muscle and tendon tissues are much more fragile when there is a lack of water.

To know your water loss, here is a very simple exercise: weigh yourself before and after running, taking into account the drink ingested.

As in this example:

Mathys weighs 65 kilos before the race

It runs for 2 hours at 24°C and 600ml of drink

Weight after race = 63.4 kg

We calculate the difference in weight before / after taking the drink into account, i.e.: 65-63.4 = 1.6 kg + 600g (600ml of drink)

Total = 2.2kg in 2 hours of effort

So I lose 1.1 liters of water per hour of running at 24°C

Note that in winter you sweat less. So try to do this exercise at about 10° and 25°. So you can estimate your needs in winter and summer.

Composition of the runner's effort drink

An effort drink must provide 3 essential things:


The water will allow 3 things:

- Hydration of tissues and cells

- Compensation for losses linked to perspiration and the chemical reactions of the body during exercise (hydrolysis, respiration, etc.)

- Finally the maintenance of blood volume.


The most important of the three: sodium (“Na” in chemistry) found in… table salt, also called sodium chloride. If you had to take only one thing before a snatch run: it would be salt water! Salt will help maintain heart pressure, nerve impulses and also compensate for losses related to perspiration. Yes, your perspiration is salty! The white jersey after the race, the eyes that burn when you sweat are all factors that attest to salty sweating.

Sodium/salt has another major impact: It increases your blood volume. And yes, we do not necessarily think about it, but an average individual has about 5L of blood. When you run, the blood is sent to the periphery of your body, to the muscles, the skin (for thermoregulation among other things) and the brain.

More blood volume means more blood for all those organs, a less straining heart and kidneys, in short, more performance. With 1 to 2g of salt in pre-competition, we can for example increase the blood volume by about 15%, simply because this salt will end up in the blood and attract water to it, making the volume "inflate" a little. of blood.


Especially if you don't eat a lot of solid foods. I recommend to my athletes about 20/40g of carbohydrates for the first hour of effort, then 50/60g for the second, 60/70g for the third up to 90g depending on the athlete and the intensity of the race. The carbohydrates in the drink are not mandatory if the diet provides enough, but for outings of more than 2/3 hours it is interesting to have a slightly sweetened drink with syrup or malto-dextrin in concentrated powder at 30/40g/L.

There you go, you are now a hydration ace for training and competition! Stay tuned for more nutritional and technical info. See you soon and have a good run!

Mathys Loridan

Mathys Loridan - Holistic Dietitian and Sports Nutritionist

Find Mathys on Instagram

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