The two percent hydration rule is 19 years old and unreplaced
Sports medicine guidance still says to drink enough during exercise to lose under about two percent of your body weight. It came from an expert panel, not a trial.
What the study found
The two percent rule is 19 years old and still the standing guidance
The number everyone quotes comes from an expert panel, not a trial. The American College of Sports Medicine advises drinking during exercise to keep body-weight loss under about two percent, and to measure your own sweat rate because sweat varies. Nothing newer has replaced it.
The caveat · Predates the salt-capsule studies
A position stand is expert consensus with no stated search and no risk-of-bias grading, and panels in this field have included researchers with sports-drink funding. It was written before the 2015 consensus on exercise-related low blood sodium and before the field studies that found sodium supplements did not prevent it. Advising people to individualise because sweat varies is not evidence that individualising improves any outcome, which is the step the personalised-hydration industry takes.