Fitness & Exercise

Marathon Runners Drink Too Much

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Of course, weather conditions play a major role. It's a good idea to train and to test for appropriate fluid intake in the same weather as you expect for your race.

Levine and Thompson point to the advice of USA Track and Field: Use thirst as your guide to fluid replacement.

But the American College of Sports Medicine (ACSM) has a different point of view.

They say that thirst is often a poor indicator of our body's fluid needs.

"Water in particular quenches the sensation of thirst before body fluid replacement is achieved, so thirst should not be the only determinant of how much fluid is consumed under such conditions," says the ACSM.