Comparison of Physical Activity Measured by Self-Reported Physical Activity and Wearable Device Xiaomi MI2 Band in Preadolescent School Children - A Pilot Cross-Sectional Study.

The purpose of this study is to compare physical activity measured by the wearable device Xiaomi Mi2 Band and self-reported physical activity by YPAQ in preadolescent school children. A pilot cross-sectional study was performed on a subsample (5%=n=60) of preadolescent children within a parallel-group feasibility intervention trial (n=1000). All children aged 9-11 years enrolled in the schools were included in the study and children with any physical disability were excluded. Self-reported physical activity was recorded through the modified version of the Youth Physical Activity Questionnaire (YPAQ) and automatic physical activity was measured by the Xiaomi Mi2 band over 7 days. Data from the Xiaomi Mi2 band was synchronized with its mobile application from where data was transferred to an excel sheet. Data on 7-day total physical activity in minutes and 7-day total step count were recorded by the Xiaomi Mi2 band. Student's t-tests were used to determine whether significant differences were present between self-reported physical activity and by Xiaomi Mi2 band. A Bland-Altman method was also used to assess the degree of agreement between the two methods of measuring physical activity. Mean ± SD age of the children was 9.6 (± 1.0) years and 31 (51.7 %) were boys. The mean ± SD time spent in physical activity reported by YPAQ was 457.5 (± 136) minutes and by the Xiaomi Mi2 band was 594.7 (± 183) minutes. The Bland-Altman plot identified a mean bias between the methods (YPAQ and Xiaomi Mi2 band) of -157.6 (95% CI: 296.3, -611.0) minutes of 7-day physical activity. Physical activity measured by a wearable device, the Xiaomi Mi2 band can give overestimated values of physical activity compared to self-reported physical activity in preadolescent school children. However, when PA is measured through step counts by the Xiaomi Mi2 band converted to minutes, it is comparable to PA measured by YPAQ.