Outcome expectancy is recognized as a determinant of exercise engagement and adherence. However, little is known about which factors influence outcome expectations for exercise among people with knee osteoarthritis (OA). This is the first study to examine the association of outcome expectations for exercise with demographic, physical, and psychosocial outcomes in individuals with knee OA.
The authors performed a cross-sectional analysis of the baseline data from a randomized trial of tai chi versus physical therapy in participants with symptomatic knee OA. Knee pain was evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Outcome expectations for exercise, self-efficacy, depression, anxiety, stress, and social support were measured using standard instruments. Logistic regression models were utilized to determine associations with outcome expectations.
There were 262 participants, with a mean age of 59.8 years and a mean body mass index of 32.1 kg/m2 ; 69.1% of the participants were female, 51.5% were white, the mean disease duration was 8.6 years, and the mean WOMAC knee pain and function scores were 260.8 and 906.8, respectively. Higher outcome expectations for exercise were associated with greater self-efficacy (odds ratio [OR] 1.25 [95% confidence interval (95% CI) 1.11-1.41]; P = 0.0004), as well as with fewer depressive symptoms (OR 0.84 for each 5-point increase [95% CI 0.73-0.97]; P = 0.01). Outcome expectancy was not significantly associated with sex, race, education, pain, function, radiographic severity, social support, anxiety, or stress.
The results suggest significant associations between outcome expectations for exercise and self-efficacy and depression. Future studies should examine how these relationships longitudinally affect long-term clinical outcomes of exercise-based treatment for knee OA.