Validity and inter-device reliability of dominant and non-dominant wrist worn activity trackers in suburban walking

Wearable activity trackers have become a popular way for general and athletic populations to measure daily physical activity and rest patterns. The validity and reliability of step count is often unknown for these devices. The aims of this study were to evaluate the validity of the step count of the Fitbit Charge HR and the inter-device reliability between devices worn on the dominant and non-dominant wrists in an ecologically valid walking setting. A secondary aim was to compare these findings with data from an inertial measurement unit (IMU). Six participants were fitted with one Fitbit Charge HR on each wrist and an IMU positioned on the left and right hip. Data from the Fitbit Charge HRs and IMUs were compared against the participant’s self-reported step count. Each participant walked the same suburban circuit whilst counting their steps. When assessed for validity, the Fitbit Charge HR was found to have a low correlation with the self-reported step count (dominant arm, ICC2, 1 = .19; non-dominant arm, ICC2, 1 =.21), underestimating the number of steps taken. In comparison, the inter-device reliability of the dominant and non-dominant wrist worn Fitbit Charge HRs was good (ICC2,1= .81). Moderate validity was found between the self-reported step count and IMUs (dominant hip, ICC2, 1 = .74; non-dominant hip, ICC2, 1 = .72). The findings suggest that inter-device measurement from dominant and non-dominant hands is reasonably reliable, however less valid as compared to more robust research-grade devices.