The Characteristics Of Physical Activity In Different Bone Mineral Density Children

Objectives:Growth period is a critical period of bone mineral deposition,in this period obtain higher peak bone mass would reduce the risk of osteoporosis,and level of physical activity in children and adolescents can promote bone density levels.In this study using accelerometer survey children daily physical activity status of the 8~9 year old children,and analyzes its characteristic in different bone mineral density children;to investigate the relationships between PA and BMD in 8~9 year old children.Methods:The Study assessed the PA of 197 children(male 109,female 109)in Beijing yuxin Primary school.the ActiGraph GT3X+ accelerometers were used to measure children PA,and the EXA-3000 Absorptiometry from Osteosys company was used to measure children BMD.Using SPSS18.0 statistical package for statistical analysis,the differences between the two groups using independent sample t test,gender,weight among groups using two-way ANOVA,the relationship between physical activity level and body composition use of partial correlation analysis,chi-square test analysis of high-intensity physical activity(MVPA)affect on children's bone mineral density,the level of significance a = 0.05.Results:boy accrued 665.6 ±139.1 counts/min and girl 579.8±112.2 counts/min of PA respectively,boy accrued 59.0min/d and girl 48.1min/d of MVPA.35% of participants could meet the WHO PA guideline(boys =49%,girls = 18%).High density group children PA(658 ±139.4 counts/min)is significantly higher than low bone mineral density group(598 ± 123.3 counts/min),P < 0.01.High density group LPA(179.9± 34.8 min/d)is significantly higher than low bone mineral density group(167.4 ±30.1 min/d),P < 0.01.High density group MPA(34.2± 9.2 min/d)is significantly higher than low bone mineral density group(30.2±7.9 min/d),P < 0.01.High density group VPA(24± 8.9 min/d)is significantly higher than low bone mineral density group(20.1±8.0 min/d),P < 0.01.High density group MVPA(58.3 ±16.7 min/d)is significantly higher than low bone mineral density group(50.3 ± 14.9 min/d),P < 0.01.The children of High and low bone mineral density group in the school day PA,LPA were higher than in the weekend.The children of High bone mineral density group have higher PA,MPA,VPA,MVPA than low bone mineral density children n the school day and weekend.High density group of childrens PA,LPA,MPA,VPA,MVPA had no significant difference in fall and winter.Partial Correlation Analysis revealed weak but significant relationships between PA,VPA,MVPA and fat content and body fat rate(-0.3 <r <-0.1,P <0.05).MVPA meet the World Health Organization(WHO)recommended amount of physical activity children receive a high density of greater than MVPA does not meet the recommended amount of physical activity for children.Conclusion:objective data indicated that Chinese youth are generally not physically active enough,in girls lower levels of PA than boys,and children are more activity in weekday,the study revealed weak but significant relationships between physical activity and body fat mass and body fat rat.Physical activity level is one of the important factors affect the level of children's bone mineral density,higher bone density group of children's physical activity level higher than that of low bone mineral density group of children,children with higher levls of MVPA to obtain the probability of high density is greater than that of the low level of MVPA children.