The other day my father emailed me some advice from a gym buddy of his that has ended up in the medical tent at the end of the Seattle Marathon three times:
It seems that the weather is so damp and cold that you do not feel you need to replace fluids (and he has done dozens of tris and marathons – including the Canadian Iron Man) and the result is that he would finish both dehydrated and hypothermic – so off to the tent for warm fluids to be pumped in.
I’ve noticed that I have indeed been drinking less as the temperature has dropped, but I think I’m still getting enough.
I also just read this excellent article by Matt Fitzgerald about nutrition and hydration for half-ironman distance races. I found the math interesting, as he recommends taking in 60 grams of carbs per hour, and letting your own thirst dictate your hydration.
As I’ve noted, I use Hammer Gel for nutrition and nuun for hydration. I was already only drinking whenever I felt thirsty (about every 10 minutes), and through experimentation settled on a gel pack every 45 minutes (but no fluid for 10 minutes before or after the gel, or else I get a side stitch). The math adds up to about 53 grams of carbs per hour.
I love it when what I’ve figured out on my own is corroborated by the experts.
Correction (11/4/2010): actually, the math adds up to 29 grams of carbs per hour. I’m not sure what happened there, but it in any case, it looks like I’m only getting about half the recommendation. Maybe I’ll need to look into alternating nuun (which has 0 carbs) with a sports drink, as I don’t think I can digest twice as much gel while running (and that’ll get expensive in a hurry!). Dangit.