Comparison of activity levels measured by a wrist worn accelerometer and direct observation in young children

Introduction: Motion sensors are mechanical and electronic devices, which detect the body movement and provide an estimate of physical activity in children and adults. However, they need to be validated against criterion methods such as direct observation. The purpose of this study was to validate a wrist worn accelerometer to quantify the physical activity of children, by comparison to direct observation using the Children’s Activity Rating Scale (CARS). Materials and Methods: Data were recorded from 42 children, aged 3 - 5 years (22 boys and 20 girls), of whom each was observed each minute for 2 hours using Children’s Activity Rating Scale (CARS) while they wore the Actiwatch. Results: The CARS score and activity counts from the accelerometer were averaged over 1- to 10-minute periods across all individuals. There was a significant positive correlation between the mean CARS scores and the mean Actiwatch counts over simultaneous 1- to 10-minute periods ranging from r = 0.41 to r = 0.63 (P < 0.001). To assess validity of the data, a cross validation method was applied. There was no significant difference between the predicted and the observed CARS scores in the validation sample. Given the data from the Actiwatch (averaged over a 5-minute epoch), the equivalent CARS score could be calculated with a 95% confidence level of plus or minus 0.74 CARS units. Conclusion: These data suggest that the Actiwatch (a wrist worn accelerometer) is a valid tool for assessing levels of physical activity in young children.