our knee is a mechanical wonder, enabling this largest of weight-bearing joints to roll, glide, and rotate. Unfortunately, its also the most abused of joints, too often the victim of long-term wear and tear. To protect your knees from premature breakdown, you need to keep the supporting muscles and ligaments strong and flexible. Here are four exercises that will help. If you feel pain or stiffness when doing any of these moves, go easy. If the pain gets worse, stop until youve talked to a doctor or therapist.