Validation of MotionWatch8 accelerometer intensity cutpoints in children

Objective. Excess body weight in children has become a serious public health concern worldwide. The Centers for Disease Control and Prevention (CDC) demonstrated that childhood obesity has tripled since the 1970s in the United States. To prevent childhood obesity, the CDC recommends that children achieve 60 minutes of moderate to vigorous physical activity each day. A variety of wearable monitors are available for objectively assessing activity but these methods are complicated by the lack of established values for the activity intensity and comparability across devices. The purpose of this study is to establish activity intensity cutpoints for the MotionWatch8 (MW8) accelerometer in children by comparison with the gold standard cutpoints established for the Actigraph GT1M accelerometer.
Material/Methods. 40 children (ages 9-13 years) from Syracuse, NY were enrolled in this study. All participants were required to wear the two different monitors on the dominant wrist as they performed a resting activity (4-minute sitting), a 4-minute slow-paced walk, a 4-minute faster-paced walk, and a 2- minute vigorous running game to mimic the different intensities a child might perform in a free-living environment. Linear regression and receiver operating PREVIEW vi characteristic (ROC) curves were performed to assess sensitivity and specificity of MW8 intensity cutpoints. Result. Mean value for each activity were positively correlated between MW8 and the Actigraph (r=0.85, p<0.001). The optimal cutpoints for differentiating sedentary from light physical activity, light from MVPA, and moderate from vigorous activity were (≤32 counts, ≥ 371.5 counts, and ≥ 859.5 counts per 30 second interval, respectively)
Conclusion. The MW8 is a simple and objective instrument for measuring physical activity in children. This study provides usable cutoff values for further testing the validity of the MW8 for measuring physical activity patterns among children