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

Abstract

Introduction: Motion sensors are mechanical and electronic devices, which detect the body movement and provide an estimate of physical activity in chil-dren 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 us-ing the Children's Activity Rating Scale (CARS). Ma-terials 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 aver-aged over 1-to 10-minute periods across all individu-als. There was a significant positive correlation be-tween the mean CARS scores and the mean Acti-watch counts over simultaneous 1-to 10-minute peri-ods 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 be-tween 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 Acti-watch (a wrist worn accelerometer) is a valid tool for assessing levels of physical activity in young chil-dren.