Most of us have been told a very simple—but entirely incomplete—story about why our knees, hips, and backs get stiff as we age. We are told it is simply "wear and tear," and that our cartilage is grinding down like the brake pads on an old car.

Because of this myth, millions of adults spend a fortune on standard glucosamine supplements, hoping to rebuild their cartilage. Yet, for many, the morning stiffness remains exactly the same.