So the same debate comes up again and again... What is the toughest athletic event??
I think I have a good view on this one, here is my background:
Typical high school jock: football and track (specialized in 400 and 300h).
I competed in decathlons through college (PR - 7160). (5008 in the hept.)
Since college I have been competing in triathlons:
I have done 2 Ironmans (PR - 10:40) and 3 half Ironmans (PR - 4:15).
I have done numerous olympic and sprint tri's, enjoyed a few of these infamous mud/obstacle races, and have competed in a few 12h and 24h MTN bike races.
In my opinion, you guys are not even discussing the toughest events in the world. Feel free to disagree with me, because I know someone will, but my personal rating would go as follows:
1) Ultra-marathons (100km +) These guys are NUTS, and they are often held in the most in-hospital places, like BADWATER! In my opinion, running these ultra distances IS MORE TAXING than biking ultra-distance.
2) Long distance bike races (200km +) There are numerous road and mtn bike races around the world that have professionals scared of the course! Try riding the Pyranees Mountain route (Trans Pyr - Spain) with 66,000 ft of elevation GAINED in just an average of ~50 hrs of riding. Or crossing over 100 mtn passes on a road bike in 10 days (Cent Cols Challenge). There are for more, far too many to even name on here that are harder than an IM tri.
3) Ironman triathlons (140.6 mi) No one who has competed can deny the pain and suffering that an IM can put you through. There is a stipulation to this one, because of the popularity. There is a HUGE difference between "finishing" and Ironman and "competing" in an Ironman. Just like the mud races and marathons, there are TONS of walkers/slow riders in these things now. 2nd stipulation, the location does matter! There are SIGNIFICANT differences in difficulty from one location to another. (Try Kona, Cozumel, or St. George instead of Arizona or Florida if you want a real challenge.) Even better, look-up the 140.6 event known only as "NORSE-MAN". That will make you cry.
4) Marathon (26.2 mi) - There is just something painful when you think about running over 20 miles. Again stipulation would be "competing", not "completing". Walking half of it doesn't make it hard anymore.
5) Decathlon (10 events, 2 days) - The pain from a solid 2 day decathlon is right up there with the pain from an Ironman. (Trust me, I have felt both enough times.) It's not even the 10 events that kill your body, it's the constant warm-up/cool-down/practice/get your jump marks/etc. between the events. In summary, there is a reason that the label the Decathlon champ at the Olympics as "The best athlete in the world!"
6) Tough Mudder (10+ miles with mud and obstacles) - I have done 5k mudders and 12 mile mudders, the 12 mile course can be physically challenging. I have to agree with some previous comments though, several of the obstacles can be seen as a good break to most competitive runners. Before people bite my head off, yes these races are hard! But I'm sorry they are not as physically punishing as the others above. Maybe if the race extended to 15+ miles WITH obstacles and mud, you could begin to talk.
7) 10k, fast 5k, mud 5k, olympic tri, sprint tri, etc... All weak-sauce compared to the above!
Just for fun, my opinion again, hardest single track & event (Besides Decathlons): either 400mH or 800m.