Running

I'm sorry sharkstar, but thats wrong.

You do need rehydrating for any lengthy run , especially in cold weather, as you dehydrate at a similar rate, but you have a reduced thirst drive. *

On the note of early drinking in marathons, some people use it as a motivating force/ rhythm, plus, little and often (+electrolytes) = good hydration. Lots and infrequently (-electrolytes) = poor hydration.

I said a few things, not sure which you think is wrong. (By the way, I am totally comfortable with being wrong. Apparently it's the new being right.) My thoughts on this topic have been shaped by Tim Noakes (whose book 'Lore of Running' I have had to buy three times now). Over-hydration is a much bigger threat than dehydration in organised races: I think hyponatria was the cause of death of the last person to die in the London Marathon, for example. Noakes' view is that we should be guided by our thirst about whether we should take on water, niceties about reduced thirst drive to one side. I find it difficult to believe that the folk who rush to the water station at the 4k mark are responding to their thirst.

More on this (in an accessible form):

http://www.runnersworld.com/article/0,7120,s6-242-302--8785-1-3-2,00.html

Google 'Timothy Noakes Hydration' for the medical papers.