Validating Fitbit Zip for monitoring physical activity of children in school: a cross-sectional study

Abstract

BackgroundModern activity trackers, including the Fitbit Zip, enable the measurement of both the step count as well as physical activity (PA) intensities. However, there is a need for field-based validation studies in a variety of populations before using trackers for research. Therefore, the purpose of the current study was to investigate the validity of Fitbit Zip step count, moderate to vigorous physical activity (MVPA) and sedentary minutes, in different school segments in 3rd grade students.MethodsThird grade students (N = 147, aged 9–10 years) wore a Fitbit Zip and an ActiGraph GT3x-BT accelerometer simultaneously on a belt for five days during school hours. The number of steps, minutes of MVPA and sedentary time during class time, physical education lessons and recess were extracted from both devices using time filters, based on the information from school time tables obtained from class teachers. The validity of the Fitbit Zip in different school segments was assessed using Bland-Altman analysis and Spearman’s correlation.ResultsThere was a strong correlation in the number of steps in all in-school segments between the two devices (r = 0.85–0.96, P < 0.001). The Fitbit Zip overestimated the number of steps in all segments, with the greatest overestimation being present in physical education lessons (345 steps). As for PA intensities, the agreement between the two devices in physical education and recess was moderate for MVPA minutes (r = 0.56 and r = 0.72, P < 0.001, respectively) and strong for sedentary time (r = 0.85 and r = 0.87, P < 0.001, respectively). During class time, the correlation was weak for MVPA minutes (r = 0.24, P < 0.001) and moderate for sedentary time (r = 0.57, P < 0.001). For total in-school time, the correlation between the two devices was strong for steps (r = 0.98, P < 0.001), MVPA (r = 0.80, P < 0.001) and sedentary time (r = 0.94, P < 0.001).ConclusionIn general, the Fitbit Zip can be considered a relatively accurate device for measuring the number of steps, MVPA and sedentary time in students in a school-setting. However, in segments where sedentary time dominates (e.g. academic classes), a research-grade accelerometer should be preferred.

A Model of Pedometer Determined Physical Activity in Primary School Children

“…Measurements conducted during academic year confirmed validity and reliability of the Fitness tracker Fitbit Charge for monitoring of pedometer determined physical activity in children, however, in segments where sedentary time dominates (e.g. academic classes), a research-grade accelerometer should be preferred (Mooses et al, 2018).…”

“…As weather influences cannot be controlled, knowledge of its influence on individual physical activity patterns may inform the design, analysis, and interpretation of future studies, especially when investigating physical activity across diverse meteorological settings and with long follow-up periods. Mooses et al (2018) investigated the validity of Fitbit Zipstep count, moderate to vigorous physical activity and sedentary minutes, in different school segments in 3rd grade students. There was a strong correlation in the number of steps in all in-school segments between the two devices (r = 0.85−0.96, p < 0.001).…”

Comparison of Polar Active Watch and Waist- and Wrist-Worn ActiGraph Accelerometers for Measuring Children’s Physical Activity Levels during Unstructured Afterschool Programs

“…Although the convergent validity does not directly imply the construct validity (i.e., degree to which the monitor measures what it is supposed to measure), it provides the form of evidence of construct validity, particularly when the counterpart monitor has known validity against a criterion measure [ 38 , 39 ]. In this regard, we compared PA intensity levels estimated from the PAW to the research-grade PA monitor, ActiGraph accelerometers, which have been previously validated in children [ 40 , 41 ] and frequently compared to different types of consumer-grade PA monitors [ 42 , 43 , 44 ]. Although the ActiGraph accelerometers have been extensively validated in the literature, the evidence is specific to the location of placement (wrist vs. waist), activity cut-points, as well as the model of ActiGgaph accelerometer used.…”

Can consumer grade activity devices replace research grade actiwatches in youth mental health settings?

“…The strength of this study is that metrics and analyses were selected a priori and the sample size was calculated to allow use of paired t tests, MAPE and bias estimates (using Bland-Altman methods). This approach is preferable to correlational analyses as these may conflate apparent agreements between ConD and ResD [32], whilst concealing the magnitude of any errors and/or whether discrepancies are primarily due to over-or under-estimation of values [33]. However, the current study has several limitations.…”