twentysixtwo

I've run 14 marathons (and countless half marathons, 30k, etc) and ridden two centuries. I haven't ridden any long races. One thing to consider is that the marathons I ran were races, the centuries weren't. That alone makes it apples and oranges.

Both take some training to do properly. Someone who is in shape for a century cannot run a marathon (without some serious pain) , someone who is in shape for a marathon cannot do a century (with the same qualification).

They are very close in many regards but I'd say a marathon is a bit more punishing. My fastest century was just over 5 hours (including breaks and pack riding for perhaps a third of the distance), my fastest marathon was just over 3-1/2.

I was beat after both but with the marathon I was pretty much wiped out for the day. I was also "feeling it" longer with the marathons.

I can't imagine what it's like to do an Ironman!