It's summer, you're running a marathon or triathlon, and you've known ''the rules'' for years: To avoid dehydration, drink as much as you can at every aid station.
Drink even if you are not thirsty because thirst is a poor indicator of how much fluid you need to replace.
Well those rules have changed. USA Track & Field, the governing body of track and field, long-distance running and race walking, has issued new guidelines for athletes to ''consume 100 percent of fluids lost due to sweat while racing.''
The USATF now recommends that athletes ''be sensitive to the onset of thirst as the signal to drink, rather than staying ahead of thirst.''
''Being guided by their thirst, runners prevent dehydration while also lowering the risk of hyponatremia (low sodium), a potentially dangerous condition increasingly seen as runners have erroneously been instructed to over-hydrate.''