Wll if it has any merit, my buddy agreed to do the 24 hours of adrenalin, (ok I conned him into it, actually i lied to him, I lied a lot, but dont tell him though...)

He is a real road head, and does about 500k a week.

He said that the 23km course to him was like doing 100k on the road, Im not so sure, because on road in 2 hours Im only 50 or 60k... but then Im still on a mountain bike...

But your upper body does take a lot more abuse, punishment and gets much more work...