What I really want to know is what is it that works - is it the high rpm, or is it the forced speed. That is, if you can pedal at 80-90 rpm by yourself is that good enough? Or is it being forced to pedal a lot faster than you really can that does the trick. Do we need another person who's faster than us or a motor on the bike, or is it good enough to just go as fast as you can?

It makes me think it must be the forced speed because both groups were working at 60% of their training heart rate, and if I were to pedal 30% faster than what felt reasonable, I think I'd be way up higher than 60%.