Expect hydration status to move; manage it without extremes
This meta-analysis pooled six full-Ironman studies and found a moderate shift toward hypohydration after racing compared with baseline. The included studies used several markers—body water, blood and urine osmolality, urine specific gravity and plasma sodium—rather than one interchangeable definition.
For athletes, the result supports planning and practice, not replacing thirst and context with a rigid body-mass rule. Know the course supply, carry a workable plan, rehearse it in comparable heat and duration and watch for signs of both under-drinking and over-drinking.
Only six studies were included, methods differed and a post-race group average does not define the safest intake for an individual. Consult the PubMed record and seek medical advice for symptoms or relevant health conditions.