Physical activity levels and functional performance in the osteoarthritis initiative: A graded relationship

Objective Physical activity improves function in adults with arthritis, but it is unknown if there is a graded relationship between physical activity and functional benefit. This study was undertaken to examine the cross‐sectional and longitudinal relationship between self‐reported physical activity and observed functional performance in adults with knee osteoarthritis (OA). Methods The Osteoarthritis Initiative cohort included 2,589 patients with knee OA (2,301 with longitudinal followup data) who were ages 45–79 years at baseline. Prospective annual functional performance was assessed for 2 years using timed 20‐meter walk tests. We used linear regression to estimate differences across physical activity quartiles in subsequent function (baseline and 1‐year activity predicts 1‐year and 2‐year function, respectively) adjusted for demographic factors (age, sex, race/ethnicity, education level, and marital status) and health factors (OA severity, knee symptoms, knee pain, knee injury, body mass index, comorbidity, depression, smoking, alcohol use, and other joint pain). Results Increasing physical activity levels had a significant graded relationship to functional performance. Adults in physical activity quartile groups from least active to most active had an average gait speed of 4.0, 4.2, 4.3, and 4.5 feet/second, respectively, at baseline (P for trend < 0.001) and 4.0, 4.2, 4.3, and 4.5 feet/second, respectively, after 1 year (P for trend < 0.001); increasing trends remained significant after adjusting for covariates. Findings were similar within sex and age groups. Conclusion These prospective data indicate a consistent graded relationship between physical activity level and better performance in adults with knee OA. These findings support guidelines that encourage patients with arthritis who cannot attain minimum recommended physical activity to be as active as possible.