Comparison of physical activity measures assessed by two different accelerometers in COPD patients

Decreased physical activity (PA) is both a consequence and a risk factor for progressive functional impairment in COPD. However, methodological approaches for its accelerometric quantification in patients are heterogeneous. The present study examined the correlation between measurements by two common accelerometers in COPD. Accelerometric data were collected in COPD patients from the German COSYCONET study over 6 full days by a Bodymedia SenseWear MF armband, worn at the upper arm all the time, and an ActiGraph GT3X device, worn at the hip (day) or wrist (night). Additionally, patients recorded their daily routine in an activity diary. Only days with a weartime>22h for both devices were evaluated. Minutes spent in the common activity levels, sedentary (SPA), light (LPA), and moderate-to-vigorous (MVPA) activity, as well as number of steps were determined per day and the correlation between both devices was examined using Spearman9s rank correlation coefficient. 18 patients were examined (10 females; mean age 69.4y) and a total number of 86 valid days were included in the analysis. Patients spent a median of 237 min/day in LPA and 83 min/day in MVPA. Over subject-specific activity means, correlation coefficients were 0.34 for SPA, 0.16 for LPA, 0.38 for MVPA, and 0.95 for number of steps per day (p Correlations between PA measures by both devices were low to moderate for activity levels and markedly better for number of steps per day. For comparative analyses of daily activity in studies which use the examined devices a primary focus on the number of steps appears to be most appropriate. Funded by the BMBF FKZ 01GI0881 and 01GI0882.