Believe it or not, this isnt that big a deal. There is a dude who a few years ago did something similar to that for some ridiculous amount of days, except he did full Ironmans each time. That 26.2k run is just the back 3rd of an ironman.
All these races/challenges mentioned in the thread are a pretty big deal no matter how you shake it. Only a small percentage of people even try marathons, and a smaller percentage complete them. These folks that do what's being discussed--sorry, but it's still impressive.
To me, the Double Ironman Triathlon athletes are really the cream IMO. Pretty impressive feat to run a double marathon, double bike segment, and double swim segment. These are exceptionally fit people.
On a side note---when I started repping a few lines in the running industry a couple of years ago, I was exposed to some amazing people as far as what they can do. One in particular is a field rep for Altra Shoes. This guy is originally from the UK and used to be an MMA Fighter. Quite successful at it, but was looking for ways to increase his stamina and found running to be the best route to take to accomplish that. Once he started running, it was only a few miles every day but kept slowly increasing his distance to where it became 20-25 every day. Turned out he was pretty fast at it as well, and wasn't long before he dropped the MMA route and went into Ultra Running full time. He said running....even the long distances....was far easier than getting smacked in the face as a way to make a living. What I find most impressive about him and others who are the Ultras....they regularly run 100 milers. One-hundred miles at a whack. That just reeks of endurance, stamina, and part crazy. Gotta tip my hat to those folks. That is nothing short of astounding to live that lifestyle.
Extreme excess cardio is bad for your heart. There have been many cases of marathon runners suddenly dying at young ages due to heart problems over the years. Autopsy results show that they had the heart of an old person.
The heart is a muscle and extreme excess use will wear it down rapidly.