Is walking good exercise for knee arthritus?

Knee Arthritis: It can be. The worst thing you can do for knee osteoarthritis is to be inactive or very overactive. It is important for your remaining cartilage to do activity. Recommend walking, on dry land or in water, and tai chi.

Yes, not only for --: The knee but generally for your whole body. In the first week or so it might your knee hurt more than usual but continue walking and build your walking distance gradually, as the knee will become less painful and feel strong, and you will better generally.