That's probably true, Bike Dutchess, but I would rather just do my athletic activity more slowly (which I already do now, at times) or find something else for fitness if I had some kind of injury that was purely cycling related. I commute and I also do a lot of "smell the roses" rides. I don't necessarily do these rides at my fastest speed, but I feel that I am still getting exercise, as say, opposed to sitting on the couch eating fried food....