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Avoidance of Physical Activity and Osteoarthritis of the Knee

June 28, 2002

Study Confirms Link Between Lack of Exercise and Increased Disability               

Findings Highlight the Mediating Role of Muscle Strength

Physical disability is one of the major consequences of Osteoarthritis (OA) of the knee. For many sufferers, routine tasks such as climbing stairs, bending down, and even walking can be daunting and painful. For decades, doctors have encouraged patients to keep moving despite pain, based on the belief that inactivity will make their condition worse. A recent study, published in the July 2002 issue of Arthritis & Rheumatism, offers solid evidence to support this hypothesis, as well as illuminates the pivotal role of muscle strength in combating the debilitating effects of OA.                                                   

Conducted by a team of OA specialists at the Netherlands Institute of Health Services Research Center in Utrecht, the study was inspired by the popular "avoidance model." "This theory states that a patient tends to avoid physical activity because of a feared or actual increase in pain," explains team leader Martin Steultjens. "In the short term, pain can be reduced by avoiding physical activity. In the long term, however, low activity levels will result in a deterioration of physical condition, especially in muscle weakness. Due to this muscle weakness, joints become less stable and their ability to carry a load is reduced. This results in increased disability. Consequently, the patient avoids activity even more, thus entering a downward spiral toward increasing physical disability."                              

Focusing on 107 patients with a mean age of 68.7 who had been experiencing OA symptoms specific to the knee for at least one year, the study measured each participant's level of disability and muscle strength through a series of physical exercises. The study also assessed patients' general avoidance of activity through an extensive questionnaire probing their habits for coping with chronic pain, from taking more frequent sitting breaks to ceasing activities altogether. After rigorous statistical analysis, researchers found a clear connection between avoidance of activity and reduced muscle strength, as well as between reduced muscle strength and increased disability. Overall, avoidance of activity accounted for 21.5% variance in disability.                              

"Although evidence in favor of the mediating role of muscle strength was obtained, it could not completely account for the effect of avoidance of activity on disability," Steultjens points out. "After controlling for muscle strength, avoidance of activity still accounted for 15.7% of variance in disability levels. This may indicate that there is a second pathway via which avoidance of activity has an influence on disability. It is possible that inactive patients develop low self-beliefs about their capabilities, which is expressed in the inability to perform certain everyday tasks, without there being clear physical reasons for this inability."                        

While indicating the need for further research into the roles of pain and fear of pain on disability, this study confirms the link between lack of activity and progressive physical deterioration in patients with OA of the knee. In addition, it makes a powerful case for the importance of routine exercise to sustain the muscle strength and mobility for all people with OA.

John Wiley & Sons