As further evidence, when I am on my fixed gear, I can crank along all day at 10 mph at 40 rpm.
EDIT: I just use the fixed gear as an example because on it, at 10 mph, 40 rpm the entire time the bike is moving is enforced by the transmission.
__________________
Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter