Think one marathon is tough? Try 50, in 50 states, on 50 consecutive days. Dean Karnazes has. He’s also run 350 miles in 82 straight hours, raced in 120-degree heat and in below-zero temperatures and thinks 31 miles counts as a short race. At 49, Karnazes is the ultra, ultra-marathoner and, surprisingly, also kind of a softy — proud of anyone who laces up their sneakers, gets out there and runs.