Ultra Marathon Man is about Dean Karnazes' life obsession with running REALLY long distances. He seems to like to do so as a means to continue to expand our consciousness to the possibilities about what our bodies can do. (And he's an SF man to boot!)
Interestingly, he was a heavy partier until his sister died, at which point he started to get serious about things, but not really about running. He became sort of a "master of the universe" kind of dude and succeeded materially, but began to feel empty.
It wasn't until he started running again that he seemed to discover purpose. And discover it he did.
He ran across the desert. He ran 199 miles. For me, the most unbelievable one was running the marathon that ended at the South Pole, unbelievable.
It's definitely an easy read and worth it (particularly if you are a work out fanatic). However, at times it was a little tough to connect to as a moderate (at best) athlete. But he does share that we all fall prey to the limitations of our mind.
One thing that I wish he would have addressed a bit more is that he finds peace and presence in pushing his body to the absolute limits. What happens when he can't do that anymore?
At some point he'll get older and certainly he'll be able to push himself to a certain extent, but not to the limits he does now. How will he find peace when that day comes?