Objective: To examine changes in mobility-related self efficacy following exercise and dietary weight loss interventions in overweight and obese older adults with knee osteoarthritis (OA), and to determine if self efficacy and pain mediate the effects of the interventions on mobility task performance.
Methods: The Arthritis, Diet, and Activity Promotion Trial was an 18-month, single-blind, randomized, controlled trial comparing the effects of exercise alone, dietary weight loss alone, a combination of exercise plus dietary weight loss, and a healthy lifestyle control intervention in the treatment of 316 overweight or obese older adults with symptomatic knee OA. Participants completed measures of stair-climb time and 6-minute walk distance, self efficacy for completing each mobility task, and self-reported pain at baseline, 6 months, and 18 months during the trial.
Results: Mixed model analyses of covariance of baseline adjusted change in the outcomes demonstrated that the exercise + dietary weight loss intervention produced greater improvements in mobility-related self efficacy (P = 0.0035), stair climb (P = 0.0249) and 6-minute walk performance (P = 0.00031), and pain (P = 0.09) when compared with the healthy lifestyle control intervention. Mediation analyses revealed that self efficacy and pain served as partial mediators of the beneficial effect of exercise + dietary weight loss on stair-climb time.
Conclusion: Exercise + dietary weight loss results in improved mobility-related self efficacy; changes in these task-specific control beliefs and self-reported pain serve as independent partial mediators of the beneficial effect of exercise + dietary weight loss on stair-climb performance.