It was suggested that I calculate just how much I sweat in an hour. I decided to do this today, in 104 degree heat, as I rode my bike through Griffith Park up to the Valley.
I weighed myself before. Then, during my hour-long ride, I sucked down two 24-oz bottles of water and a Gu pack. I felt constantly thirsty. Normally the bike provides some air conditioning because you're moving at a decent pace. Not today. I felt hot and awful.
My worry with hydration during a long event, such as the upcoming olympic distance tri, is not only of drinking too little, but possibly of drinking too much. Slower endurance athletes like me are at risk of hyponatremia, a too low sodium concentration in the blood from drinking more fluid than what their body is losing.
Even after drinking so much, I weighed myself -- I had lost a half a pound! In that hour of cycling, I had lost fifty-six ounces of fluid. Almost two liters!
Maybe the moral of the story is to not ride in ridiculous heat like this. But at least now I know that in extreme heat, I sweat a LOT.