Psychological factors affecting isokinetic trunk strength testing in patients with work-related chronic low back pain.

Psychological factors are assumed to play a major role in pain-related work disability. Assessment of pain-related disability using a functional capacity evaluation, usually includes assessment of trunk strength and range of motion. Isokinetic strength testing is a method used to measure strength and function of isolated muscles and has been reported to be an objective, quantifiable assessment of trunk function. Given that psychological factors are purported to play a role in pain-related disability, it would be important to assess their influence on measurement of physical function. The present study was conducted to assess the influence of psychological variables on isokinetic trunk strength performance. One hundred and eighty-six consecutive male outpatients referred to a work-rehabilitation center were given a functional capacity evaluation. All patients had been out of work for at least 3 months with the chief complaint of low back pain. The evaluation included isokinetic trunk strength testing and measurement of psychological variables (pain levels, distress, pain coping, pain behavior, somatization, expectation to return to work) that have been known to contribute to pain-related disability. Data analyses revealed significant correlations among psychological variables and measures of trunk strength and function. The findings provide support for a relationship between psychological variables and isokinetic strength testing performance.