Studies have shown that isometric strengthening helps people with osteoarthritis of the knee. Isometric strengthening is muscle-strengthening exercise without movement, in which a person applies a force against a resistant object--for example, pushing against a brick wall. This study will test the effectiveness of a portable isometric exercise device for home use that guides a person through an exercise program using various forms of feedback. We will look at whether people exercising with the device achieve better outcomes (results) in pain, stiffness, strength, and functional measures compared to people who do not use the device or people exercising according to printed material from arthritis organizations.