There's a reason why so many extreme athletes have the Ironman insignia tattooed on them - because they want everyone to know that they are crazy! Incidentally, as I was coming toward miles 11 and 12 today, there was a guy moaning about his knee. We were so far into the race, I had to offer him encouragement to just finish, 'we were so close!'. For me, it was just another half marathon, but knowing what I know now, I wish he would've taken the bio-feedback. He ended up sprinting past me some 10 - 15 minutes later. I was a little dehydrated, so I didn't need to turn it into a footrace. When you're in the peanut gallery, you are only competing against yourself. As the army-looking tee-shirt ahead of me said, 'Be All that You Used to Be'. You get lots of time to think during these races. I enjoyed that, and the girls holding the 'I admire your stamina' posterboards...
I saw that poor bastard in a wheelchair after the race. Yes, running can be addictive, there are documented cases of very healthy people dying from drinking too much water before or after a race. So I guess where I'm going with this is to try to push yourself in a natural way. Some people naturally go to the extreme, but it doesn't destory their knees. Know thyself. I want to be able to run half marathons for the rest of my life. That sounds like a pretty good outcome.