The upshot is this: The data supports drinking when thirsty. The data do not support drinking at all water stops. Drinking at all water stops puts one at risk for hyponatremia. This phenomenon occurs over time as someone stated, thus, the deconditioned athletes have more time to drink. High performers finish before they have time to drink enough.

"Did the study address any difference between runners who drank water and runners who drank sports drinks or other liquids with ion concentrations closer to serum?" as people have posed on this thread.



Sports drinks do not help here. To paraphrase in layman's term from a medical site.... think of a sports drink as having the same solute concentration as blood (isontonic) . When ADH (Antidiuretic hormone) is stimulated (which it is without going into complicated renal physiology) the urine concentration becomes at least twice the serum concentration. If we assume urine concentration is twice serum concentration, then it is also twice the concentration of the sports drink. If we drink in a liter of sports drink, we only urinated 500 ccs of urine to excrete the solutes (thanks to antidiuretic hormone being released). This leaves 500 cc of new free water - which dilutes the serum and lowers the sodium. The other problem with sports drinks is the glucose - which increases water absorption, making the sports drink more effective at increasing free water (and thus lowering serum sodium).