It is recommended that individuals participate in 150 minutes of moderate intensity physical activity or 75 minutes of vigorous physical activity each week. Commercially-available PA monitors are becoming popular for everyday use. These PA monitors provide feedback on steps, energy expenditure, moderate-to-vigorous intensity physical activity (MVPA), and sleep quality, with new models introduced to the public at an increasing rate. Whether these devices provide the consumer with accurate information is not well understood.
PURPOSE: To examine the accuracy of a wrist worn commercial device (Fitbit Charge) and a hip worn device (Fitbit One) in regard to steps and MVPA under free living conditions, compared to a research-grade accelerometer (Actigraph GT3X).
METHODS: Participants (n=17, Mean SD, Age: 27.8 9.0; BMI: 24.7 4.2) wore 3 devices (Actigraph GT3X, Fitbit Charge and Fitbit One) for 7 consecutive days. Participants were told to go about their regular daily activities while wearing all 3 devices at the same time. The GT3X was worn on the right hip.
RESULTS: Paired t-tests showed that mean steps per day between the Actigraph (10510.6 2443.7) and the Fitbit Charge (12537.7 3936.2) differed significantly (P = 0.016). Mean steps per day between the Actigraph and the Fitbit One (11726.7 11726.7) also differed (P = 0.001). Steps between the Fitbit Charge and Fitbit One did not differ (P = 0.195). No significant differences were found in active minutes recorded between any of the devices (53.0 15.2, 52.0 42.9 and 52.8 28.9) for the Actigraph, Charge and One, respectively). Bland-Altman analysis concluded that the Actigraph and Charge (P = 0.02) and the Actigraph and One (P < 0.01) did not agree for steps, whereas the Charge and the One did agree (P = 0.2). All three devices showed good agreement with regard to MVPA.
CONCLUSION: Results showed that the 2 commercial devices did not agree with the Actigraph, a widely used PA monitor for research purposes, in mean step data. However, the devices did show good agreement with regard to MVPA, suggesting that these commercial devices may provide useful feedback for individuals seeking to achieve the current public health PA guidelines for MVPA.