[One interesting experiment to try: One day ride 100 miles then run 26.2 miles. After recouperating enough days, the next time try running 26.2 miles then riding 100 miles.[/QUOTE]
It's not as difficult as it sounds. A lot easier than an ironman. I've done several 50k's then gone to work. Then, the next day or two done 90 to 135 mile rides. I could do that relatively easy, but couldn't figure out how to put together a good nutrition plan for an ironman. I think I've figured it out now while training for a 100 mile mountain bike race.