What’s more difficult, an Ironman or a long NFL season? He doesn’t hesitate: triathlon
“Not even close,” he said. “I’m telling you right now, I have a whole new respect for triathlon athletes, people who run, swim, bike. It is a whole new world. My world is all quick, fast, punch you in the face, run away. This is like, you’re going to sit here in your own mind for 12 hours and you’re going to question for a good hour of it why you’re doing it. At the same time, it’s going to be grueling and challenging. It’s so much harder than playing football, I don’t care what anyone says.”
A quote from NFL offensive lineman Alex Boone after doing an Ironman.
That being said I personally would choose a hard bike ride over getting hit by someone 6’6” and 300 pounds