Physical activity and hydration: the importance of drinking well during exercise

I work out, I sweat, I know I have to drink. But do I really know when, how much, and what? Hydration around exercise is a seemingly simple area, but rich in received ideas: drink only when I am thirsty (too late), drink sports drinks for any type of effort (often unnecessary), or on the contrary never drink during exercise for fear of having a stomach ache (counterproductive).

Water represents 60% of body weight and is involved in absolutely all physiological functions: transport of nutrients, thermal regulation, muscle contractions, cognitive functions. Understanding how to manage your hydration before, during and after exercise can significantly improve your performance, recovery and overall health.

1. What happens when I get dehydrated

Dehydration has progressive and rapidly deleterious effects on physical and mental performance:

The thirst signal is only triggered at 1 to 1.5% dehydration, after performance has already started to deteriorate. This is why waiting until you are thirsty to drink is a reactive and insufficient strategy during physical exercise.

2. My water needs depending on the effort

Water requirements during exercise vary considerably depending on intensity, duration, temperature and individual profile. Here are the practical benchmarks validated by research:

• ●Before exercise: make sure you are well hydrated beforehand, clear to pale yellow urine. Drink 400 to 600 ml in the 2 hours before exercise. Do not overhydrate: hyperhydration dilutes electrolytes.

• ●During exercise (less than 60 min): 150 to 250 ml of water every 15 to 20 minutes. No need for sports drinks for a short, moderate-intensity effort.

• ●During exercise (60 to 90 min, moderate intensity): 200 to 300 ml every 15 min. If the heat is significant or the sweating is high, add a pinch of salt or a light isotonic drink.

• ●During long exercise (more than 90 min): 30 to 60 g of carbohydrates per hour in addition to hydration. Isotonic drink or gel + water. Rehydration alone with pure water over long periods can induce hyponatremia (dangerous dilution of sodium).

• ●After exercise: drink 150% of weight loss (weigh before and after if necessary). Ex: 1 kg lost = 1.5 to drink in the following hours. Clear urine as a goal.

3. Water alone or sports drinks: what to choose?

Sports drinks (isotonic, energy) are very well marketed, and often useless or even counterproductive for most amateur athletes. Here is a clear guide:

4. Signals of good and poor hydration

The simplest way to assess your hydration level is the color of urine, a reliable and free indicator:

• ●Pale to light yellow (lemon color): optimal hydration. This is the objective to maintain throughout the day and particularly around exercise.

• ●Dark yellow or amber: moderate dehydration. Drink more, especially if exercise is planned.

• ●Brown or very dark: severe dehydration. Requiring immediate rehydration and interruption of intense activity.

• ●Colorless: may indicate overhydration. Not systematically problematic, but to be monitored during very long efforts (risk of hyponatremia).

Other signs to be aware of: headaches at the end of a session (often dehydration), muscle cramps (loss of sodium and magnesium), unusual fatigue the day after exercise (incomplete fluid recovery).

5. Hydration and cognitive performance at workHydration does not only concern sport, it has direct effects on daily cognitive performance. Studies show that mild dehydration (1-2%) is enough to impair short-term memory, concentration and performance of demanding cognitive tasks.

In practice: drinking 1.5 to 2 liters of water per day (part of which comes from food) is sufficient for the vast majority of adults under normal conditions. Needs increase with heat, physical exercise, stress and air-conditioned environments (which dry out the ambient air). A health check may include an assessment of hydration habits, particularly relevant for people engaging in regular physical activity.