This could also be called "How to Get Motivated to Do Crazy Hard Athletic Stuff".
You probably don't have tons of time for pleasure reading, but if you can squeeze a page in while on the elliptical machine at the gym or one chapter at a time after the kids go to bed, I highly recommend these books I've read recently:
The Perfect Mile by Neal Bascomb
Ultimate Fitness by Gina Kolata
Swimming to Antarctica by Lynne Cox
Why We Run: A Natural History by Bernd Heinrich
Ultramarathon Man: Confessions of an All-night Runner by Dean Karnazes
None of the are how-to books. There are no training plans or diets. Just stories about athletes. I'm sure there are many others that I just can't think of at the moment.
What books you would recommend to inspire one's inner athlete?