The Science of Sport is one of the best blogs I've found on "the Internets". They just wrote a post on Mind over Matter? that I think is certainly worth a read. They analyze the very idea of "mental strength" (for lack of a more articulate word) over physiology, and conclude that there's really no way to know. But don't let the obvious conclusion stop you from reading the post. It's their analysis that is top-notch. Here's one snippet:
Now, the obvious extension of this is that if your brain makes the decision, then you can "trick" the brain, or discipline it, into delaying that decision, which would allow you to run or ride faster before that point is reached. Instead of slowing down, you'll hang in there, guts it out, suffer through the pain, because your performance will be improved. It's classic mind over matter.
Unfortunately, this doesn't work, for much the same reason that people are not very successful at committing suicide by holding their breath! It doesn't matter much how badly you want to go, your physiology will win in the end.
They've definitely given me some things to mull over. My next post will touch on these in more detail.