Validity and usability of low-cost accelerometers for internet-based self-monitoring of physical activity in patients with COPD

Background: The importance of regular physical activity for patients with COPD is well established. However many patients do not meet the recommended daily amount. Accelerometers might provide patients with the information needed to increase physical activity in daily life. Objective: Our objective was to assess the concurrent validity and usability of two low-cost internet-connected accelerometers. Methods: First, to assess validity we conducted a field validation study with patients who wore two low-cost accelerometers (Fitbit and PAM) at the same time along with a validated multisensor accelerometer (SenseWear Armband) for forty-eight hours. Data on energy expenditure assessed from registrations from the two low-cost accelerometers were compared to the reference criterion. Usability was examined in a cross-over study with patients who, in succession, wore the Fitbit and the PAM for seven consecutive days and filled out a sixteen item questionnaire with regards to the use of the corresponding device. Results: The agreement between energy expenditure from SenseWear Armband with METs estimated by the Fitbit and PAM was good (r=0.77) and moderate (r=0.41), respectively. With regards to the usability both the Fitbit and PAM were well rated on all items with no significant differences between the two devices. Conclusions: The low-cost Fitbit and PAM are valid and usable devices to measure physical activity in patients with COPD. Therewithal, as patients showed willingness to monitor physical activity for longer periods, these devices may be useful in long-term self-management interventions aiming at increasing physical activity levels in these patients.