Dehydration : excessive fluid loss

Loss of body fluids that degrades performance and can become dangerous.

A 2% body weight loss from dehydration is enough to reduce aerobic performance by 10-20%. It causes increased fatigue, cramping and cardiac drift (higher HR at the same effort). In long-distance racing, the goal is not to replace 100% of fluid losses : aim for 70-80% to avoid the inverse risk (hyponatremia). Urine color remains the best indicator: pale yellow = well hydrated.