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 Community Healthy Activities Model Program for Seniors (CHAMPS) Questionnaire and, in a subsample, by tri-axial accelerometers. OMERACT-OARSI dichotomous responder criteria was used for clinically meaningful improvement at follow-up. Associations between baseline self-reported PA by CHAMPS and outcomes of responders vs. non-responders (reference group) were assessed using logistic regressions, adjusting for demographic covariates. We compared objectively-measured PA by accelerometry between responders vs. non-responders using Wilcoxon tests.

Results: Our sample consisted of 166 participants with knee OA who completed both baseline and 12-week post-intervention evaluations: mean age 60.7 year (SD 10.5), BMI 32.4 kg/m (6.9), 119 (72%) women, and 138 (83%) OMERACT-OARSI responders. Neither time spent in total PA (OR 1.00; 95% CI 0.96, 1.03) nor time in moderate-to-vigorous (MV) 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 level (subjective report or objective measurement) was not associated with whether an individual will achieve favorable treatment outcomes after a 12-week exercise intervention, suggesting that regardless of pre-intervention PA level, individuals will likely benefit from structured exercise interventions.