Determination of Best Cut off Value of Activity Count in Diagnosis Exercise Intensity of Adolescents by Receiver Operating Characteristic（ROC） Curve Analysis

Objective:To determinate the best cut off value of different exercise intensity in adolescents by ROC Curve and aim to elevate validly the daily physical octivity level in future.Methods:The rest and the 8 activities was synchronous monitor by portable gas analyzer(Cosmed K4b2) and triaxial accelerometer(ActiGraph GT3X) in 80 health Chinese children aged 11¹4 years(40 boys and 40 girls).AUC(Area Under Curve) was to judge the diagnostic function of AC(Activity Count) for distinguishing the low,moderate or high exercise intensity.The maximum Youden value was used to determine the best cutoff point of different exercise intensity.Results:The vertical is predominant in various activities and the change trend of ACxis1,VM2 and VM3 is similar.The ROC curve can determine the best cut off point of ACxis1,VM2 and VM3 in diagnosis of exercise intensity(AUC∈0.708,0.890,P<0.001).The best cutoff point of 3 METs,6 METs and 9 METs was respectively ACxis1(2 151 counts/min,3 761 counts/min,3 783 counts/min),VM2(4 935 counts/min,6 009 counts/min,6 169 counts/min) and VM3(9 600 counts/min,9 900 counts/min and 10 296 counts/min).Conclusions:ACxis1,VM2 and VM3 can reflect effective human moving state and the best cut off value of them can diagnosis valid the exercise intensity in adolescents.The best cut off value of light physical activity was ACxis1<2 152 counts/min,VM2<3 761 counts/min,VM3<3 783 counts/min;moderate physical activity was 2 151 counts/min≤ACxis1<4 935 counts/min,3 761 counts/min≤VM2<6 009 counts/min,3 783 counts/min≤VM3<6 169 counts/min,large physical activity was 4 935 counts/min≤ACxis1<9 600 counts/min,6 009 counts/min≤VM2<9 900 counts/min,6 169 counts/min≤VM3<10 296 counts/min,and vigorous activity was ACxis1≥9 600 counts/min,VM2≥9 900 counts/min,VM3≥10 296 counts/min.