ETINGER, W. H. Jr. and R. F. AFABLE. Physical disability from knee osteoarthritis: the role of exercise as an intervention. Med. Sci. Sports Exerc., Vol. 26, No. 12, pp. 1435–1440, 1994. Osteoarthritis (OA) of the knee is a common, nonfatal, chronic condition that causes pain and physical disability in older people. Persons with knee OA report difficulty with activities that require ambulation and transfer from the sitting to the standing position. Physical disability from knee OA is the result of a complex interplay among the severity of disease, pain, comorbid conditions, psychosocial factors, and deficits in physical capacity such as low aerobic work capacity and lower extremity muscle weakness. These deficits in physical capacity may be correctable with exercise training. Short-term studies and report less pain and disability with exercise training. However, the long-term effectiveness and safety of exercise in persons with knee OA remains unknown.