Motivation

I don't know if it's all these olympics commercials, my mid-life crisis, or being the (old) mother of a young child but I've been motivated to get in my best physical condition yet.  I'm working out like a freak, signing up for races and considering the most ridiculous thing of all...a marathon.  Ok, a half...but even that is stupid for this runner-hater.  I'm even manipulating myself into signing up for a cancer fund raising race so I'm extra-motivated to stick with it.  What's going on?