In rehab at the end of last year I was able to use am exercise bike for short periods. It seems like a really good workout for my knee and ought to be good cardiovascular work, too. My doctors were supportive of the idea, so I renewed my gym membership and have actually been back a couple of times this week. I am definitely the wonkiest looking guy in the gym, but it definitely feels good being here and being able to do this kind of activity.