To understand the effects of leg strengthening exercise, we will study the effects of strength training of the legs in four groups of people: (1) osteoarthritis (OA) with knee pain; (2) OA without knee pain; (3) no OA but elderly with knee pain; and (4) normal elderly with no OA or knee pain. In each of the first three groups, we will look at whether people who do strength training have less pain and/or slower progression of x-ray signs of OA over 30 months than people who perform nonstrengthening, range-of-motion exercises. We are including the fourth group to find out whether people with OA (groups 1 & 2) have the same response to strength training as healthy elderly people, and whether those with knee pain (groups 1 & 3) have the same response to training as those without joint pain.