In my experience as someone who has had osteoarthritis in the hips for 20 odd years, I find cycling is actually very good for the condition as it seems the movement helps with circulation and suppleness of the joints, and because there is little force on the joints (non-weight bearing exercise) I don't experience any pain associated with the activity. I used to play a lot of golf and would be very stiff and sore after 18 or 36 holes. Even now, a couple of hours of walking around the mall I will start to limp and have pain and discomfort. However, it seems I can cycle any amount of time/distance without any ill effects. Last week I cycled 266 miles, and yes my quads were sore by the end of the week, but pain from arthritis was nil and it rarely even crosses my mind that I have the condition. The fact that I've lost around 30lbs since starting cycling also benefits the condition and my overall health in general. That's only my experience of course and I am not qualified to comment on whether cycling will tend to aggravate arthritis in others.