Inexpensive personal activity monitors have recently gained popularity with the general public. Given the current wide-spread use of these devices, it is important to ensure that users are attaining accurate information compared to previously validated measures.
PURPOSE: To compare the accuracy of the Fitbit Force™ and One™ activity monitors in measuring steps per day and time spent in different intensities of activity with the ActiGraph GT3X™tri-axial accelerometer.
METHODS: Twenty-two women, 18-26y.o. with a BMI of 23.24 ± 3.26kg/m2 wore two Fitbit Ones TM (Bra and Waist respectively), a Fitbit Force TM (Wrist), and an ActiGraph GT3X™(Waist) for 7-consecutive days. ActiGraph™ data was processed using Actilife™ V5.1.1 and the Freedson equation activity cut points. Fitbit™ data was processed using their proprietary online software. A multivariate analysis of variance (MANOVA) was used to compare steps per day and time spent in light, moderate and vigorous intensity activities between the four devices. A post-hoc test of the least squared difference was used to determine where any differences occurred
RESULTS: The activity monitors differed in time spent in light F(3,19)= 3.16, p>.05) and vigorous (F(3,19)= 3.16, p>.05) intensity activities. Post-hoc comparisons revealed that the GT3X™ differed from all three Fitbit™ devices in the measurement of time spent in light (GT3X= 89.92±36 min, Force=419.97±129.22 min, Bra=379.93±122.2 min, Waist=392.75±114.78 min) and vigorous activities (GT3X=7.05±9.63 min, Force=36.91±27.7 min, Bra=31.29±18.53 min, Waist=30.45±18.3 min). There was no difference found in the number of steps per day or minutes of moderate intensity activity recorded between the four devices.
CONCLUSIONS: Fitbit™ activity monitors compare well to other previously validated objective activity monitors in the measurement of steps per day and time spent in moderate intensity activities. However, Fitbit™ devices may not accurately quantify the time spent in light and vigorous intensity activities, and therefore may not be the ideal solution for individuals’ personal activity monitoring needs.