Concurrent Validity of the MOX Activity Monitor Compared to the ActiGraph GT3X

Background: The It's LiFe! monitoring and feedback tool embedded in primary care practice is promising in helping people to achieve an active lifestyle. This new tool consists of an activity monitor (the MOX), which is connected to a smartphone application and to a Web service for patients and care providers. The aim of this study was to develop thresholds for the moderate and vigorous activity categories and examine the concurrent validity of the MOX in relation to the ActiGraph (Pensacola, FL) GT3X in healthy participants and chronically ill patients (chronic obstructive pulmonary disease and type 2 diabetes) in a laboratory situation and during daily living. Materials and Methods: Participants wore the two activity monitors simultaneously on the lower back. An incremental treadmill protocol was executed by 8 healthy adults and 10 patients. For daily living measurements, 15 healthy adults and 12 patients wore the devices for 6–7 days. Daily living data were corrected for non-wear time, using diary information. Results: On the treadmill there was an excellent correlation between the ActiGraph and MOX counts (mean r =0.99 in healthy participants and mean r =0.98 in patients). Correlation during daily living was moderate (mean r =0.72) in healthy adults and good (mean r =0.82) in patients. Bland–Altman plots showed no perfect agreement between the two devices in minutes per category. However, a histogram of misclassified minutes showed that misclassification occurred around category thresholds. Conclusions: The MOX is capable of measuring physical activity and can be used in the It's LiFe! intervention.