Osteoarthritis of the knee (KOA) is the most common cause of disability not only in the United States but also in Japan. KOA is associated with pain, quadriceps weakness, swelling, instability, decline of range of motion, physical function, and quality of life (QOL) (1). In particular, quadriceps weakness may contribute to incident symptomatic and progressive disease (2, 3), cause functional limitations and disability (4) and increase the risk of mortality (5). Both aerobic exercise and resistance exercise are recommended for the treatment of people with knee osteoarthritis (KOA) (6). However, exercise at a moderate or severe intensity is often a problem for people with knee pain or a history of knee injury.