I ride my bike for heart and knee therapy. My left knee is especially bad, with the cartilage all gone and bone grinding against bone. Knee replacement surgery is in my near term future. Meanwhile, my orthopedic surgeon and physical therapist have told me to either swim or ride a bike faithfully. The secret is flexing the knees, while the bike seat is carrying most all of my body weight. And it works! The swelling and pain are greatly reduced when riding my bike daily. Seems odd, doesn't it?