I had a model B, then C from 1987 to 1995. Didn't row that much. In 2005 I was diagnosed with a severe case of osteoarthritis in the left knee. Gave up on the treadmill, got a model D because it is quiet. I don't row that hard, just nice and easy. Have a prosthesis in the left shoulder (bicycle accident 1998), and wear a brace on the left knee except when rowing. I average 70,000 plus meters a week. C2 is easy on the joints. The C2 gives me enough leg work so I can do my annual 26.2 mile walk for the Jimmy Fund.