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.
| Level of dehydration | Physiological effects | Effects on performance |
|---|---|---|
| 1% of body weight | Slight rise in heart rate, onset of thirst | Early decline in endurance performance |
| 2% | Marked thirst, rise in body temperature, less elastic skin | 20 to 30% drop in performance, reduced concentration |
| 3 to 4% | Marked fatigue, headaches, possible nausea, dark urine | Exercise very difficult, risk of heatstroke |
| 5% and above | Severe symptoms, possible seizures, medical emergency | Activity must be stopped |
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:
| Type of drink | Composition | When it is useful | When it is useless or not advised |
|---|---|---|---|
| Water | Plain water | Efforts under 60 min, daily hydration | Never useless; it is the reference |
| Isotonic drink | Water + electrolytes (sodium, potassium) + carbohydrates (6-8%) | Efforts over 60-90 min, intense heat, heavy sweating | Short efforts, adds unnecessary calories |
| Energy drink (with caffeine) | Water + carbohydrates + caffeine and/or other stimulants | Long effort, competition afternoon, alertness at stake | Before sleep, in sensitive people, in children |
| Coconut water | Water + natural electrolytes (mainly potassium) | Rehydration after moderate exercise, natural alternative to isotonic drinks | Not enough sodium for very intense efforts |
| Diluted fruit juice | Water + carbohydrates + vitamins, diluted 50% | Recovery snack after moderate exercise | Not suitable during exercise (concentration too high) |
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.
💡 Tips to remember
- Dehydration of only 2% of body weight reduces physical performance by 20 to 30% and degrades concentration. Waiting until you're thirsty is already too late.
- Urine color is the best indicator of hydration: light yellow = optimal, dark yellow = drink more. Simple, free and reliable.
- For efforts of less than 60 minutes, water alone is sufficient. Isotonic sports drinks are only useful after 60-90 minutes of exercise or in high heat.
- Drinking 150% of the weight lost after exercise (1 kg lost = 1.5 kg to drink) is the best documented rehydration strategy to optimize muscle recovery.
- Slight dehydration at work (1-2%) is enough to degrade short-term memory and concentration. Drinking regularly throughout the day is also a cognitive performance strategy.
Further reading
