Accuracy of Three Activity Monitors in Patients with Chronic Obstructive Pulmonary Disease: A Comparison with Video Recordings

Low physical activity and sedentary behaviour characterise the lives of patients with chronic obstructive pulmonary disease (COPD). Using activity monitors, assessment of both aspects are possible, but many outcomes are not well validated. The aim of this study was to assess the accuracy and equivalency of three activity monitors regarding steps, body position and their ability to differentiate between periods of physical activity and inactivity. Fifteen patients with COPD (8 females; median (interquartile range, IQR) age, 64 (59-69) years; forced expiratory volume in 1 second, 37 (28-48)% predicted; 6-minute walk distance, 444 (410-519) m) were enrolled. The DynaPort ADL-monitor, the DynaPort MiniMod monitor and the SenseWear Armband Pro 3 monitor were assessed. Subjects performed a structured protocol alternating physical activity and inactivity while simultaneously wearing all three monitors and being video recorded. The mean difference (limits of agreement) in step count from monitors compared to manual step count was -69 (-443 to 305) for the ADL-monitor, -19 (-141 to 103) for the MiniMod and -479 (-855 to -103) for the SenseWear Armband. Compared to the video, the sitting time was 97 (94-100)% when measured by the ADL-monitor and 121 (110-139)% by the MiniMod. Standing time was 114 (107-122)% when measured by the ADL-monitor and 68 (47-106)% by the MiniMod. Activity monitors are not equivalent in their abilities to detect steps or body positions. The choice of monitor should be based on the particular outcome of interest.