Something else I've read a lot about is the "central governor theory" which basically means that you start out an event with your brain programmed for that distance, and it allots energy/speed out to your muscles so there will be just enough to make it to the distance you originally planned. Where you run into problems is when you come upon an unexpected difficulty, like a big hill you didn't know about, and your brain says "Oh, no, I didn't allot for this- I'd better make her feel extra tired, so she doesn't use up the energy I'd planned." But- if you pre-ride/drive the course, and are familiar with the features, especially difficult parts like hills, your brain (subconsciously) takes this into consideration at the beginning and you won't get that tiredness before you even _get to_ the obstacle, because your brain will be expecting it. (This was tested with some sort of experiment- and I posted about it several months ago, so if you search, you could probably find it.)