quadriceps weakness is one of the most common and disabling impairments seen in individuals with knee osteoarthritis (OA) 13) . Sufficient quadriceps and hamstrings strength, both isometric and dynamic, is essential for undertaking basic activities of daily living, such as standing and walking 14) . Muscle strength testing has revealed that those with knee OA have a 25% to 45% loss of knee extension strength and a 19% to 25% loss of knee flexion strength 15–18) , compared with similarly aged controls. There are 3 factors thought to contribute to knee extension and flexion weakness in those with knee OA: muscle atrophy, failure of voluntary muscle activity, and apparent weakness from increased antagonist muscle co-contraction 19) .