"Unbreakable: The Western States 100" [1] came to mind after you reminded me of the Barkley documentary. “The Barkley Marathons, the race that eats it’s young” seems more human and better grounded than "Unbreakable", but "Unbreakable" captured the excitement of running ultra marathons so completely for me.
1: https://www.youtube.com/watch?v=zy1as6CTYXI