Back pain is one of the most common causes of disability in industrialized nations. Despite this, the variables that contribute to disability are not well understood and optimal measurement strategies of disability have not yet been determined. The present study sought to comprehensively assess the strongest predictors of physical activity as a proxy for disability. New patients in a chronic pain specialty clinic completed questionnaires to assess the predictors of physical activity and engaged in 5 days of home data collection wearing an accelerometer to assess physical activity in daily life, which is how disability was operationalized in this study. Analysis of repeated measures patient data revealed that, of 3 composite variables each representing a theoretical model, the model representative of operant factors significantly predicted physical activity. Subsequent analyses showed that pain sensitivity, fear avoidance, and solicitous spousal responses account for a significant amount of the variance in physical activity. These findings suggest that external sources of reinforcement or punishment may serve to influence physical behavior beyond that of internal cues such as fear avoidance or pain. Implications for treatment are discussed, including the potential benefits of specifically incorporating the patient's sources of operant reinforcement or punishment into treatment.
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