| Objective:The aims of this study were(1)to examine the trends in and distribution characteristics of physical activity among Chinese children aged 6～17 years old from 2004 to 2015,and to explore the factors influencing physical activity,laying an evidence base for formulating physical activity intervention;(2)to develop and validate physical activity measurements for Chinese children aged 6-17 years old,providing technical support for monitoring the trends of physical activity and evaluation of physical activity intervention among Chinese children in the future.Methods:In study one,data on physical activity were extracted from the "China Health and Nutrition Survey" project.Firstly,a total of 4341 children aged 6～17 years old who participated in at least one round of follow-up surveys from 2004 to 2015 were included.Random-effects ordinal regression models were applied to investigate the trends in the levels of physical activity and sedentary behaviors,and repeated measures mixed models were applied to examine the trends in and distribution characteristics of physical activity volume and time spent in leisure-time sedentary behaviors(LTSB)in consideration of the non-independence of the measure data,taking the community as a random effect and adjusting for socio-demographic differences across survey years.Secondly,a total of 1779 children aged 6～17 years old who participated in at least two rounds of follow-up surveys from 2004 to 2015 were included.Longitudinal quantile regression models were applied to explore the changes and the influencing factors at each quartile of physical activity volume and time spent in LTSB.In study two,after a comprehensive literature research,expert review and preliminary investigation,firstly,the "6-to 17-year-old Chinese Children Physical Activity Questionnaire(CCPAQ)" was developed to measure the type,intensity,frequency and duration of weekly physical activity,secondly,an appropriate wristband activity monitor were selected,as the subjective and objective measurements of physical activity for Chinese Children aged 6～17 years old,respectively.Using the ActiGraph WGT3X-BT accelerometer as a standard reference,the CCPAQ and the wristband activity monitor were validated in terms of time spent in physical activity and physical activity energy expenditure etc.A total of 120 children from the North and the South of China were recruited for this study.The participants wore the accelerometer and the wristband activity monitor at the same time for 7 days consecutively.Two CCPAQ surveys were conducted upon the completion of monitoring activities and repeated after an interval of 24 hours.The Intraclass Correlation Coefficient(ICC)was used to assess the test-retest reliability,and spearman rank correlation,kappa test,χ2 test and Bland-Altman analysis were applied to test the calibration validity.Factor analyses were used to test the structural validity of the CCPAQ.In addition,the validity between the CCPAQ and the wristband activity monitor was also compared.Results:1.Trends in and correlates of physical activity among Chinese children aged 6～17 years old from 2004 to 2015The prevalence of physical inactivity among Chinese children aged 6～17 years increased from 76.0%in 2004 to 81.5%in 2015(OR=1.51,95%CI:1.19～1.90,P<0.001),of which an increase of 10.0%was observed in boys,and no significant change in girls.From 2004 to 2015,the average weekly volume of physical activity decreased from 41.7±1.6 METs·h/week to 35.9±1.7 METs·h/week(F=5.16,P<0.001),of which,volume of in-school exercise decreased by 4.6 METs·h/week(F=25.04,P<0.001).From 2004 to 2015,the time spent in LTSB rose from 23.9±0.6 h/week to 25.7±0.6 h/week(F=15.17,P<0.001).In particular,time spent in screen-based entertainment increased by 2.9 h/week(F=20.37,P<0.001),with more profound increases observed for the time on the internet(increased by 2.5 h/week,F=50.69,P<0.001)and games(increased by 1.3 h/week,F=25.37,P<0.001)sub-categories.The proportion of Chinese children with average daily screen time below 2 hours declined from 71.6%in 2004 to 61.4%in 2015(OR=0.51,95%CI:0.42～0.63,P<0.001),and a decreasing trend was observed in both boys and girls.From 2004 to 2015,the volume of physical activity in Chinese children aged 6～11 years old,residing in communities with medium or high urbanization level,or residing in the South decreased by 6.2 METs·h/week(F=5.28,P<0.001),5.9 METs·h/week(F=2.67,P=0.031),8.5 METs·h/week(F=2.59,P=0.037),5.9 METs·h/week(F=4.28,P=0.002),respectively.However,no significant changes were observed among those aged 12～17 years old,residing in communities with low urbanization level,or residing in the North.Chinese children residing in communities with low urbanization level showed greater increase in LTSB than those residing in communities with high urbanization level.Similarly,those residing in rural areas showed greater increase in LTSB than those residing in urban areas.Children aged 12～17 years old(P<0.001),of ethnic minorities(P≤0.020),residing in urban areas(P≤0.034)or residing in the north of China(P≤0.019)showed higher volume of physical activity than their counterparts at each quartile level.The median and upper quartile in the volume of physical activity were lower among girls than that in boys(P<0.001).Children in high-income families(P≤0.019),residing in communities with high urbanization level(P≤0.002)or residing in urban areas of China(P<0.001)showed higher LTSB than their counterparts at each quartile level.2.Validation of physical activity measurements for Chinese children aged 6-17 years old The ICC for the CCPAQ developed in this study,measuring time spent in physical activity,different intensities of physical activity,different types of physical activity and physical activity energy expenditure,were 0.63 to 0.93(P<0.001).The Spearman rank correlation coefficient(rs)for the CCPAQ measuring time spent in physical activity and sedentary behaviors were both of 0.32(P<0.001).The calibration validity of the CCPAQ measuring physical activity energy expenditure was moderate(rs=0.58,P<0.001).There was no significant difference in estimating the prevalence of physical inactivity between the CCPAQ and the accelerometer(χ2=0.327,P=0.568).The structural validity of the CCPAQ measuring the modes and types of physical activity were tested using factor analysis,a second-order 4 factors model(χ2/df=1.41)and first-order 7 factors model were fitted well(χ2/df=1.61),consistent with the CCPAQ structure.The ICC for the wristband activity monitor selected in this study,measuring time spent in physical activity and different intensities of physical activity,physical activity energy expenditure and steps were 0.71 to 0.88(P<0.001).The calibration validity for the wristband activity monitor measuring time spent in physical activity,moderate-to-vigorous intensity physical activity and physical activity energy expenditure was median(rs:0.51-0.63,P<0.001).The calibration validity of the wristband activity monitor measuring steps was strong(rs=0.72,P<0.001).There was no significant difference in the estimated the prevalence of physical inactivity between the wristband activity monitor and the accelerometer(χ2=0.807,P=0.369).The validity of the wristband activity monitor measuring time spent in physical activity and different intensities of physical activity was higher than that of the CCPAQ,while the validity was similar between the two measurements in terms of estimating physical activity energy expenditure and the prevalence of physical inactivity.The CCPAQ can distinguish the types and modes of physical activity effectively,while the wristband activity monitor can measure the number of daily steps accurately.Conclusion:A declining trend of physical activity among Chinese children aged 6～17 years old was observed from 2004 to 2015,in particular,physical activity volume significantly decreased in Chinese children aged 6～11 years old,residing in communities with medium or high urbanization level,or residing in the South.Urbanization can promote both of physical activity volume and time spent in LTSB among Chinese children.The CCPAQ developed in this study was proved to be feasible in the measurements of weekly physical activity and types of physical activity,as well as the wristband activity monitor in the evaluation of time spent in moderate-to-vigorous intensity physical activity and steps.This study suggested that(1)urgent actions should be taken to promote the in-school physical activity and reduce the screen time of Chinese children aged 6～17 years old,and targeting key populations and regions to improve physical activity and curb sedentary behaviors;(2)the CCPAQ should be applied as the main means to comprehensively measure physical activity of Chinese children aged 6～17 years old,if conditions permit,combined using the wristband activity monitor. |
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