Association between Pre‐intervention Physical Activity Level and Treatment Response to Exercise Therapy in Persons with Knee Osteoarthritis—An Exploratory Study

OBJECTIVE: Examine whether pre‐intervention physical activity (PA) level is associated with achieving a positive treatment response of pain and/or function improvement after a 12‐week exercise intervention in participants with knee osteoarthritis (OA). METHODS: We performed a secondary analysis of a randomized, single‐blind comparative effectiveness trial showing similar treatment effects between Tai Chi mind‐body exercise and standard physical therapy intervention for knee OA. Baseline PA was assessed by a Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire and, in a subsample, by tri‐axial accelerometers. The Outcome Measures in Rheumatoid Arthritis Clinical Trials–Osteoarthritis Research Society International (OMERACT‐OARSI) dichotomous responder criteria was used for clinically meaningful improvement at follow‐up. Associations between baseline self‐reported PA by the CHAMPS questionnaire and outcomes of responders vs. nonresponders (reference group) were assessed using logistic regressions, adjusting for demographic covariates. We compared objectively measured PA by accelerometry between responders vs. nonresponders using Wilcoxon tests. RESULTS: Our sample consisted of 166 participants with knee OA who completed both baseline and 12‐week postintervention evaluations: mean age 60.7 year (SD 10.5), body mass index 32.4 kg/m(2) (6.9), 119 (72%) women, and 138 (83%) OMERACT‐OARSI responders. Neither time spent in total PA [odds ratio (OR) 1.00; 95% confidence interval (CI) 0.96, 1.03] nor time in moderate‐to‐vigorous PA (OR 1.01; 95% CI 0.93, 1.09) at pre‐intervention were associated with being a responder. Similar findings were observed in 42 accelerometry sub‐cohort participants. CONCLUSION: Pre‐intervention PA levels (subjective report or objective measurement) were not associated with individuals achieving favorable treatment outcomes after a 12‐week exercise intervention, which suggests that regardless of pre‐intervention PA level, individuals will likely benefit from structured exercise interventions.