Validity of the Fitbit wearable activity monitor to estimate step counts in free-living conditions in ambulatory children and youth living with disability.

Abstract

Purpose: To assess the validity of the Fitbit ChargeHR versus a research-grade accelerometer (ActiGraph GT3X) for estimating daily step counts in free-living conditions in ambulatory children and youth living with physical and non-physical disabilities.

Materials and methods: Children and youth living with disability (n = 29; median age 10 years (IQR: 8-13), 55% boys; n = 2 with mobility aid) wore the GT3X ActiGraph accelerometer (hip) and the Fitbit ChargeHR (wrist) for seven days. Inter-device agreement in steps/day was assessed by intraclass correlation coefficients (ICCs) and Bland-Altman plots. A receiver operating curve (ROC) was used to determine a Fitbit step-count cut-point that corresponds to meeting physical activity guidelines (defined as ≥60 min of moderate-to-vigorous physical activity per day).

Results: Overall, we found an ICC = 0.861 (p < 0.001) between daily step counts measured by the two devices. Bland-Altman analyses revealed a mean difference ("bias") between the devices with the Fitbit recording, on average, 1,388 more steps/day than the accelerometer (Limits of Agreement (LoA) 1,741 to -4,518 steps per day). The ROC revealed a Fitbit cut-point of 12,272 steps/day corresponding to meeting guidelines.

Conclusions: Fitbit ChargeHR devices tend to overestimate daily step counts, but may still provide useful estimates of step counts and patterns in children and youth living with disability.