Originally Posted by chasm54

Cycling is extremely easy on the joints. In fact, many people with dodgy knees from running and other sports (me, for instance) find that cycling isn't just possible for them, but improves their condition. The fact that it is so kind to the joints is one reason why so many cyclists stay fast, and continue to do high mileages, well into old age.

Obviously poor positioning and grinding a big gear can cause problems, but for most people cycling doesn't give rise to arthritis. Tendinitis is more common, I believe.