At my last gym my spin instructor was a mountain biker and we jokingly referred to his class as "mountain bike class" rather than spinning. All joking aside, it was a great class and REALLY helped with riding outside. I need to get my butt to a spinning class or two a week since riding outside just doesn't seem to be in the books for now. I don't want to lose ALL of my bike-endurance - that is a very different thing from my metabolic/lifting work. My only concern is the older bikes don't really fit me and my whiplash still isn't quite healed - but I need to give it a shot. If my neck isn't up to it then I will need to spend more time on the trainer at home.