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A study on determination of best critical value of steps/min in diagnosis exercise intensity for Chinese adolescents by receiver operating characteristic (ROC) curve analysis

Lin Zhu, Peijie Chen

Purpose: This study aims at evaluating the diagnostic value of steps/min in differentiating exercise intensity through Receiver Operating Characteristic (ROC) curve so as to determine the best cutoff point of steps/min for Light Physical Activity (LPA), Moderate Physical Activity (MPA) and vigorous physical activity (VPA) for Chinese children. Method: With the synchronous monitor of the portable gas metabolic analyzer (Cosmed K4b2) and three-axis accelerometer (ActiGraph GT3X), 60 subjects of 11-14 years old middle school students (being evenly composed of males and females) would be tested with resting and 3~8km/h walking/running exercises. The experimental data were used to draw a ROC curve. Result: The result showed that there was no gender difference (P>0.05) between males and females on steps/min and exercise intensity when they conducted the same activity; the corresponding AUC of 3METs and 6METs was 0.906(P<0.05) and 0.895(P<0.05) respectively, which manifested that steps/min had great value to diagnose the exercise intensity. The best critical point of steps/min for 3METs and 6METs determined by the maximum Youden value was 121 steps/min and144 steps/min respectively with high sensitivity (0.744~0.944) and low 1-specificity (0.035~0.160). Steps/min was effective to differentiate the best critical point of exercise intensity, and the consistency examination result was also good. Conclusion: It can be concluded from this study that steps/min is effective to diagnose the exercise intensity and the best critical value of steps/min for the adolescents to do MPA is 121 steps/min to 144 steps/min and ≥144 steps/min for VPA.