Endurance races last long enough that your body will give you clues as to how it is going to be feeling in the coming hours. It is an important skill to learn to read these signs. I failed horribly at this during the 2005 24 Hours of Moab.
The above photo was taken on my last full day lap at Moab. At the time of the photo I was feeling very good. I was on pace to meet my goals, and was very excited about the coming night. 2 laps later I was puking. I had become dehydrated. I had done a very poor job of replacing electrolytes. Take a look at a detail of the image:
The arm warmers are white with salty sweat. That is not normal for me 6 hours into an event. I should have seen that, and known immediatley what it meant. I could have prevented the puke fest, and continued on through the night. Instead I was balled up in pain in my sleeping bag.
Everyone’s body is different. If you can learn the language your body speaks, it can go a long way in preventing future bonks.