Many people struggle to run a mile; others can knock out a 10K on a whim. A few brave souls take on "ultramarathons" — races longer than 26.2 miles (42.2 kilometers). But how far can a human run ...

Because books can do that. Dean Karnazes’s Ultramarathon Man inspired hundreds or thousands of people to try ultrarunning, Colin Fletcher’s books inspired probably thousands of people to take ...