Behaviour-based movement cut-off points in 3-year old children comparing wrist- with hip-worn actigraphs MW8 and GT3X

Introduction Behaviour-based physical intensities have not undergone rigorous calibration in long-term recordings of 3-year-old children’s sleep/activity patterns. This study aimed at (i) calibrating activity counts of motor behaviour measured simultaneously with MotionWatch 8 (MW8) and ActiGraph (GT3X) in 3-year-old children, (ii) documenting movement intensities in 30s-epochs at wrist/hip positions, and (iii) evaluating the accuracy of cut-off agreements between different behavioural activities. Methods Thirty 3-year-old children of the NorthPop cohort performed six directed behavioural activities individually, each for 8-10 minutes while wearing two pairs of devices at hip and wrist position. Directly observed naturally-occurring behaviours included: watching cartoons, recumbent story listening, sit and handcraft, floor play with toys, engaging in a walk and a sprinting game. Receiver-Operating-Curve classification was applied to determine activity count thresholds and to assign context-guided, physical activity composite classes. Results Activity counts of MW8 and GT3X pairs of wrist-worn (r = 0.94) and hip-worn (r = 0.79) devices correlated significantly (p < 0.001). Activity counts at hip position were significantly lower compared to those at the wrist position (p < 0.001), irrespective of device type. Sprinting, floorball/walk and floorplay assigned as ‘physically mobile’ classes achieved outstanding accuracy (AUC >0.9) and two sedentary and a motionless activities assigned into ‘physically stationary’ classes achieved excellent accuracy (AUC >0.8). Conclusion This study provides useful cut-offs for physical activity levels of preschool children using two different devices. Contextual information of behaviour is advantageous over intensity classifications only, because interventions reallocate time among behaviours, which allows to establish dose-response relationships between behavioural changes and health outcomes. Our comparative calibration is one step forward to inform behaviour-based public health guidelines for 3-year-old children. ### Competing Interest Statement The authors have declared no competing interest.