Researchers funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) have gained new insights into the value of select measurements of muscle performance in people with osteoarthritis of the knee. Their findings shed further light on the ability of such factors to predict the therapeutic effects of exercise in people with the disease.

Knee osteoarthritis (OA) is a common disorder affecting more than 4.3 million adults in the United States. The disease results in significant pain and disability. Weakness of the quadriceps muscles (in front of the thigh) is common in people with knee OA, and many affected individuals are unable to fully "activate" these muscles. (Activating a muscle means that all of the available muscle fibers are used during a maximum effort muscle contraction.) A team of physical therapists and doctors at the University of Pittsburgh, led by G. Kelley Fitzgerald, PT, PhD, FAPTA, sought to determine whether baseline quadriceps activation scores in people with knee OA would affect their gains in muscle strength following an exercise program. Their findings recently appeared in Arthritis & Rheumatism.

Fitzgerald's study included 111 people age forty or older with knee OA. Following measurement of quadriceps strength and quadriceps activation (QA), participants were randomly assigned to one of two six-week therapeutic exercise programs. Both programs included lower extremity stretching, range of motion and strengthening exercises, and aerobic exercises. However, the second regimen also included "dynamic agility" and balance training activities.

Following the exercise therapy, Fitzgerald's team again measured quadriceps strength and QA. They discovered that baseline QA was significantly associated with quadriceps strength both before and after the therapeutic exercise program. But contrary to their expectations, QA scores at baseline did not predict which participants would benefit most from either program. In fact, there was a wide range of variation in strength gains. Fitzgerald concluded that factors other than QA score may be more valuable in determining which patients with knee OA will respond best to quadriceps strengthening exercises.

The mission of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the U.S. Department of Health and Human Services' National Institutes of Health (NIH), is to support research into the causes, treatment, and prevention of arthritis and musculoskeletal and skin diseases; the training of basic and clinical scientists to carry out this research; and the dissemination of information on research progress in these diseases. For more information about NIAMS, call the information clearinghouse at 301-495-4484 or 877-22-NIAMS (free call) or visit the NIAMS Web site at

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Reference: Scopaz KA, Piva SR, Gil AB, Woollard JD, Oddis CV, Fitzgerald GK. Effect of baseline quadriceps activation on changes in quadriceps strength after exercise therapy in subjects with knee osteoarthritis. Arthritis Rheum. 2009 July 15;61(7):951-7.

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