RESUMEN
Objective@#To explore the optimal correlation between physical activity and body fat indexes during pubertal transition,and to provide a reference for reducing obesity of adolescents and making the interventional measures.@*Methods@#A total of 366 junior high school students were recruited. ActiGraPh-GT3X accelerometer was used to collect daily physical activity data for 7 days. InBody 520 was used to assess body composition. Pearson partial correlation was used to analyze the correlation between physical activity level and body composition. Curve fitting was used to construct the optimal model of physical activity and body fat index.@*Results@#There was no gender difference in waist height ratio and fat mass between boys and girls(P>0.05), and the percentage of body fat in boys was significantly lower than that in girls(t=-4.73,P<0.01). There was no gender difference in light physical activity (LPA) time between boys and girls (P>0.05).The time of moderate physical activity (MPA), moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) in boys was significantly higher than that in girls (P<0.01).The sedentary time in boys was significantly lower than that in girls (t=2.64，3.23，4.24，-2.85，P<0.01). For overweight and obese group, less time was spent in LPA, MPA, MVPA and VPA compared with normal group, while more time spent in sedentary time. Waist height ratio, fat mass and body fat percentage among male and female adolescents were positively correlated with sedentary time (F=14.63，15.54,P<0.01), while negatively correlated with LPA, MPA and MVPA time (P<0.05).@*Conclusion@#The body fat percentage was higher in boys than in girls,and the level of physical acitivity was even higher in boys than in girls.The adolescents of normal weight has got a higher level of physical activity than over weight or obese adolescents. Long-term adherence to certain physical activities and appropriate reduction of sedentary time are of vital importance for teenagers to effectively control their weight and prevent chronic diseases.