Knee pain due to osteoarthritis (OA) usually is an often disabling in older adults. Clinical guidelines recommend exercise and physical activity as a core treatment for adults with OA, with associated benefits including pain reduction, improvement in physical functioning, reduction in the risk of comorbidities, and improved quality of life. To conducted secondary data evaluation of a randomised controlled trial of assignment interventions (ISRCTN: 93634563). Participants were adults ≥45 years old with knee pain attributable to OA (n = 514). Crude and adjusted cross-sectional and longitudinal relations between baseline Self-Efficacy for Exercise (SEE).  Positive Outcome Expectations for Exercise (POEE), Negative Outcome Expectations for Exercise scores, and physical activity level, at baseline, three months, and six months (evaluated by self-report using the Physical Activity Scale for the Elderly [PASE]). Moreover, essential increases in physical activity level (from baseline to 6-month follow-up) were investigated using multiple linear and logistic regression.

The cross-sectional relationship was found between SEE and PASE scores (β = 4.14 [(95% CI) 0.26, 8.03]) and POEE and PASE scores (β = 16.71 [95% CI 1.87, 31.55]), regulate for sociodemographic and clinical covariates. The longitudinal relation was found between baseline SEE and PASE scores at three months (β = 4.95 [95% CI 1.02, 8.87]) and six months β = 3.71 (0.26, 7.16). Moreover, baseline POEE and PASE at three months (β = 34.55 [95% CI 20.13, 48.97]) and six months (β = 25.74 [95% CI 11.99, 39.49]), adjusted for baseline PASE score and intervention arm. However, no significant associations with necessary increases in physical activity level were found.

Greater assignment self-efficacy and more positive exercise outcome expectations were related to higher current and future physical activity levels.