Dehydration is one of the most common performance killers I see with clients. Even 2% body weight loss through fluid loss significantly impairs performance. But overhydration is also dangerous, potentially causing hyponatremia. The key is individualized hydration strategies.
How Much Do You Need?
Fluid needs vary dramatically based on sweat rate, which depends on exercise intensity, temperature, humidity, clothing, and individual physiology. Some people sweat 0.5L per hour; others lose 2-3L per hour during intense exercise.
To estimate your sweat rate: weigh yourself before and after training (without clothes, after toweling off). The difference in pounds is approximately the fluid loss in liters (1kg = 1L). Add 250-500ml for each pound lost to account for continued fluid losses through urine.
Pre-Exercise Hydration
Begin exercise euhydrated by drinking 16-20oz of water 2-3 hours before training, and another 8oz about 20 minutes before. If your urine is dark yellow in the morning, you're likely starting in a dehydrated state.
During Exercise
For sessions under 60 minutes, water is usually sufficient. For longer or more intense sessions, electrolytes become important:
- Sodium: 300-600mg per hour during exercise for most people
- Potassium: Important for muscle function, found in many sports drinks
- Magnesium: Important for energy production, lost through sweat
Post-Exercise Rehydration
Replace 150-200% of fluid losses after exercise (if you lost 1L, drink 1.5-2L). Include sodium in your post-workout drink unless your next meal is soon. Plain water without electrolytes can actually worsen hydration if sodium is too low.
Signs of Dehydration
- Thirst (though thirst appears after you're already dehydrated)
- Dark yellow urine
- Decreased performance and early fatigue
- Headache
- Dizziness
- Muscle cramps
