My first DNF (1999 Vermont 100 mile Endurance Run) was caused by heat "problems". This section is dedicated to my own personal research and experience.
Nice post, thanks for sending it to the list. After VT I've been researching and studying hot weather, replenishment and stomach problems and I've concluded, prior to your post, that most of what you said makes a lot of sense for my own personal application. I have one question however and that has to do with optimal fluid intake.
You mention no more than 30 ozs per hour. Would that include conditions like we just went through? It would seem that at least 40ozs was necessary and perhaps 50+ would have been best. Now I'm not sure I could have handled that so I've begun to train myself to drink more rather than less. Experience has shown me that my stomach will also revolt during long hot periods or when I don't mix up types of drink when I try to drink a lot but I'd better re-learn my hydration needs and habits so as not to let what happened at VT happen again.
From: Paul Schmidt
To: Kevin Sayers
Subject: Re: Nausea
Dr. Noakes feels that for some people drinking more than 750 ml of fluid may lead to problems. His suggests that for some people the constant movement and stress of running decreases the rate of fluid uptake in the intestines. Therefore, when the ingestion rate exceeds that of absorbtion, fluids "back up" or acummulate in the stomach and may lead to vomitting. I'm not quite sold on this therory, but I believe an increase in sodium intake will change the osomolarity of the fluid and aid in absorbtion. This may decrease discomfort that often accompanies larger fluid intakes (30-40oz). Noakes suggests taking up to .5 grams of Na/hour. I think with added sodium (up to 1 gm/hr)we may be able to increase our fluid intake to say 40 oz/hr.
Certainly, the critical factor is keeping the body core temperature down. I have always thought that hot weather races should have kids pools filled with cold water and ice at the aid stations, although sitting a cold stream would help. I think mixing up differnt types of cold drinks just makes it easier to drink more because we get tired of the same tasting drinks over the period of the race. From our brief conversation during the race, it sounded like you were not taking in enough sodium. I took in about 40 Succeed caps during the VT, 3/hour during the heat of the day, with 2/hour the rest of the time. Kevin Setnes told me that he did the same. IMHO (as we are all an experiment of one).