Does Physical Activity Confound Race Differences in Osteoarthritis-Related Functional Limitation?

Objective. This study sought to determine the extent to which physical activity confounds the relation between race and the incidence of osteoarthritis (OA)-related functional limitation.Methods. OA Initiative study participants with or at increased risk of knee OA who wore an accelerometer were included. Race was self-reported. Average time spent in moderate to vigorous physical activity (minutes per day) based on ActiGraph uniaxial accelerometer data was assessed. Functional limitation was based on the following: (1) inability to achieve a community walking speed (1.2 m/s) standard, (2) slow walking speed (<1.0 m/s), and (3) low physical functioning based on a Western Ontario and McMaster Universities OA Index (WOMAC) physical function score greater than 28 of 68.Results. African American (AA) participants (n = 226), compared with White participants (n = 1348), had a higher likelihood of developing functional limitation based on various measures. When adjusted for time in moderate to vigorous physical activity, the association between AA race and inability to walk a community walking speed slightly decreased (from relative risk [RR] 2.15, 95% confidence interval [95% CI] 1.64-2.81, to RR 1.99, 95% CI 1.51-2.61). Association between AA race and other measures of functional limitation mildly decreased (slow walking speed: from RR 2.06, 95% CI 1.40-3.01, to RR 1.82, 95% CI 1.25-2.63; low physical functioning: from RR 3.44, 95% CI 1.96-6.03, to RR 3.10, 95% CI 1.79-5.39). When further adjusted for demographic and other clinical variables, only the association between race and low physical functioning (WOMAC) significantly decreased and no longer met statistical significance.Conclusion. Greater physical activity is unlikely to completely make up for race differences in OA-related functional limitation, and other barriers to health equity need to be addressed.