Purpose: Many ActiGraph accelerometer cutoff points and equations have been developed to classify children and youth's physical activity (PA) into different intensity levels. Using a sample from the Chinese City Children and Youth Physical Activity Study, this study was to develop new ActiGraph cutoff points for moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) for Chinese children and youth and to compare the classification accuracy to that of a set of existing cutoff points.
Method: A total of 367 Chinese children and youth (179 boys, 188 girls, ages 9-17 years old) had their resting metabolic rate measured and completed six 5-min treadmill walking/running tests (tested at different speeds: 3 km x h(-1), 4 km x h(-1), 5 km x h(-1), 6 km x h(-1), 7 km x h(-1), and 8 km x h(-1)), one unit of the 3rd broadcast gymnastics (Version 3, Xi-Wang-Feng-Fan and Wu-Dong-Qing-Chun), and 2 sets of table tennis exercises (continuous attack and multiple balls). Participants wore 1 ActiGraph GT3X accelerometer on their right hip during each test, and their oxygen consumption and heart rate (HR) were measured using Cosmed K4b2 and Polar HR transmitter. The participants were randomly divided into a calibration group (n = 331, 90%) and a cross-validation group (n = 36, 10%). Using the receiver-operating characteristic curve, the data from the calibration group were used to determine the cutoff points for MVPA and VPA. Using the data from the cross-validation group, classification accuracy of different cutoff points was evaluated through kappa statistics, sensitivity, and specificity.
Results: A set of new cutoff points of counts per minute (CPM) was generated using the calibration data, and these cutoff points were proven to be more accurate compared with those developed in previous studies.
Conclusion: When using ActiGraph accelerometers to measure the Chinese children and youth's PA, we recommended using the cutoff points of CPM > or = 2,800 to define MVPA and CPM > or = 4,000 for VPA.