Hate to throw more rain on your parade but rowing is another sport that is very tough on the knees. Puts a similar load on the knees as doing squats, repeated over and over again.
As for biking, I have two friends who have really bad knees and have both gotten into biking as a last resort and are now nuts about it. One of them did a 100-mile ride this summer.
Last edited by goran_ace; 10-30-2012 at 06:23 AM.