I think it depends on your doctor! I also have bad knees (arthritis) and also torn cartilage in one knee. My doctor says its better to move more, not less. A knee that isn't used stiffens; the muscles around it start to atrophy, and because these muscles otherwise absorb some of the shock that moves up the leg with every step, a stiff knee has to take on more of the body's weight than a supple one. In a study of men and women with knee osteoarthritis, Mayo Clinic researchers found that those with the strongest quad mscles had less knee pain and better physical function than those with the weakest. I take Glucosamine and Chrondroitin supplements (recommended by my doctor) and a high dose of Ibuprofen he prescribed every day so that I can keep working out. I still do lunges, squats, Cathe's jumps, etc. Also I try to alternate more low impact workouts like Low Max, Low Impact Circuit, and Low Impact Step on occassion. I stretch alot (see examples of good stretches from the "Strong Knees" DVD available on Collage. My doctor has not prohibited me from doing any of these exercises. If you can modify, keep exercising as much as you can, which actually will improve your osteoarthritis! At least that has been the case for me.