It is true that chronically drilling oneself out on a bike may predispose to atrial fibrillation, or AC separation.
But cycling is not all bad. Take this case from the most recent NEJM as a striking example of one of the many benefits of cycling.
It is a 56 year old man with completely disabling Parkinson’s disease, who simply cannot walk or axially turn, but amazingly, can ride a bike flawlessly. The video is incredible. It is 45 seconds–an eternity in the blogosphere–so be patient. (Also, disable the pop-up blocker to view)
I knew there was something magically soothing to the rhythmic pleasures of a finely tuned pedal stroke, and the forward acceleration that ensues.