In a recent Chinese systematic review and meta-analysis, researchers reviewed 17 randomized-controlled trials (RCT) that examined how resistance exercise affects knee pain, stiffness, and general physical function among 1,705 patients (mean age 63.5 years) with knee osteoarthritis.
Why Does Exercise Seem to Work?
Knee osteoarthritis has been associated with “decreased muscular strength, increased ligament stiffness, and alterations in muscle activation patterns. According to Su et al., resistance exercise may “normalize muscle firing patterns and joint biomechanics,” which may reduce pain and cartilage wear-and-tear and improve movement.
They also cautioned that, in some cases, patients “feel better” because exercise itself improves mood, which can lead to a positive reporting even if there is no improvement in function. The placebo effect may also contribute to some positive outcome reports.
Limitations and Considerations
It is possible that the review and meta-analysis have missed key studies that are not in English or Chinese. Some of the studies Su et al. reviewed did not report intent-to-treat which may affect the review's bias. Other limitations include the omission of patients who had undergone knee surgery, lack of long-term effects of resistance exercise on knee osteoarthritis, and few double-blinded studies among the 17 RCTs.
Despite these limitations, there are a few gems that clinicians, therapists, and trainers could still apply to their work. Current evidence indicates that the type of exercise is not a big factor in alleviating knee pain and stiffness. The leg press, knee extension, and knee curl have some benefits as well as hip abduction and adduction (with resistance) exercise.
Or almost anything that you enjoy doing. Having knee osteoarthritis does not necessarily mean that you stop moving and sit all day. In fact, many physical therapists and physicians encourage patients with knee osteoarthritis to move more, but not too much.
A prospective cohort study that included almost 2,600 middle-age and older subjects with knee osteoarthritis found those who had a higher degree of physical activity in their lifestyle had a greater performance function in the 20-meter walk test. The authors stated, “These findings are also informative for persons with knee OA who perceive these goals are not attainable possibly due to pain or stiffness.” (5) Thus, it is possible that these folks with painful or stiff knee can gradually develop better function and independence with the right care and encouragement.
So if you do have knee osteoarthritis yet it is not impeding your movement much or at all, pick up your favorite running or dancing shoes, and keep on doing what you love — in moderation.
1. Tanaka R, Ozawa J, Kito N, et al. Efficacy of strengthening or aerobic exercise on pain relief in people with knee osteoarthritis: a systematic review and meta-analysis of randomized controlled trials. Clinical rehabilitation. 2013; 27: 1059–1071.
2. Su Y, et al. The effects of resistance exercise in patients with knee osteoarthritis: A systematic review and meta-analysis. Clinical Rehabilitation. 2015;
3. Bennell KL, Hunt MA, Wrigley TV, et al. Role of muscle in the genesis and management of knee osteoarthritis. Rheumatic diseases clinics of North America. 2008; 34:731–754.
4. Sled EA, Khoja L, Deluzio KJ, et al. Effect of a home program of hip abductor exercises on knee joint loading, strength, function, and pain in people with knee osteoarthritis: a clinical trial. Physical therapy. 2010; 90: 895–904.
5. Dunlop, DD et al. Physical activity levels and functional performance in the osteoarthritis initiative: a graded relationship. Arthritis and Rheumatism. 2011 Jan;63(1):127-36. doi: 10.1002/art.27760.