tulip, I like your thinking. It's just as important to think about what keeps us happy, sane, patient, add-admirable-trait-at-will as to how exercise affects our bodies.

That said, what I like most about biking as exercise and especially bike commuting is the everydayness and usefulness of it. Even the days that aren't "whee!" I'm still getting from A to B on my own power and am also using my body the way I feel it was meant to be used, simple movement over time, nothing extreme.