Longitudinal Study on Trajectories of Physical Activity and Its Effect on Physical Fitness in Children

Objective:To explore the trajectories and characteristics of physical activity and sedentary behaviorduring 3 years from kindergarten to primary school among children.The effect of different trends of moderate-vigorous physical activity and body mass index on the physical fitness and their interaction were analyzed.Method:A total of 306 preschool children were recruited by 7 kindergartens in Shanghai, 127 (79 boys, 48 girls) who participated in both baseline and follow-up study.PA was objectively measured by accelerometer Acti Graph GT3 X+.Physical fitness tests were completed according to thecorresponding national Fitness Measurement Standards.Multifactor covariance analysis with MVPA trend group, BMI group as independent variables, physical fitness scores in follow-up stage as dependent variable was carried out.Result:Regardless of workday or weekend, time in children's sedentary behavior at baseline was significantly lower than follow-up stage, while time in light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) were significantly higher than follow-up stage.Boys' MVPA time onworkdays and weekends were significantly higher than girls (t=3.55, P<0.01;t=2.86, P<0.01) .The main effect of MVPA trends, BMI group on boys' grip strength were significant (F=2.736, P<0.05;F=4.753, P<0.05) .The main effect of both MVPA trends, BMI group andtheir interactionson boys' upper abdominal muscle strengthwere significant (F=3.126, P<0.05;F=5.705, P<0.05;F=7.038, P<0.01) .The main effect of MVPA trends on the boys' agility was significant (F=3.463, P<0.05) .There was a significant interaction between MVPA trends and BMI group on boys' aerobic fitness (F=2.837, P<0.05) .Conclusion:During 3 years, sedentary behavior on workdays and weekends significantly increased, while LPA and MVPA decreased.There is a significant correlation between children's LPA, MVPAon workdays at baseline and follow-up, but not between sedentary behavior.Continuous active MVPA or increasing MVPA havepositive effects on grip strength, upper abdominal muscle strength and agility in boys.Increasing MVPA time in normal weight boys may have positive effects on upper abdominal muscle strengthand aerobic fitness, but not in obese boys.