Variability in moderate-to-vigorous physical activity assessment: Comparing tri-axial accelerometry cut-off points in children

The present study aimed to investigate the effect of the most frequently used cut-points (CoPs) on quantification of active children, as well as to analyse children physical activity (PA) quantification using vertical axis and vector magnitude (VM). The sample comprised 303 children (160 girls) aged 6 years -10 years. Height, weight and BMI were assessed to control for confounding variables related to PA levels. The tri-axial accelerometer was used for seven consecutive days of moderate-to-vigorous physical activity (MVPA) and sedentary behaviour (SB). A general linear model was used; the agreements of all CoPs were analyzed by Kappa index. Freedson CoPs presented the highest percentage of active children (100%) for males and females during the weekdays, weekend, and for total assessed days. The Mattocks CoPs revealed the lowest proportion of active children for the weekdays (2.97%), weekend days (3.30%), and for the seven assessed days (1.65%). The interpretation of accelerometer results must be critiqued in respect to whether children are meeting publically adopted PA guidelines. The growing variety of analytical approaches and CoPs employed to analyse and evaluate accelerometer data in children makes it difficult to compare findings across different studies.