Recommendations Of Physical Activity For Enhancing Health In Chinese Children And Adolescents

Compelling evidence has indicated that regular physical activity (PA) has a widerange of health benefits for children and adolescents, including reduced risks ofobesity, cardiovascular disease, loss of bone density, and improvement of mentalhealth. Therefore, World Health Organization (WHO) and lots of countriesrecommended a minimum of60minutes of moderate-to-vigorous PA (MVPA) foryouth. However, epidemic data show that there is a large portion of youth indeveloped countries including U.S. being physically inactive. PA levels of youth inChina are also not optimistic with only22.7%of9-18years old youth taking part inMVPA as indicated in a national survey in2010. To date, large-scale PA data ofChinese youth mainly were collected by questionnaires rather than objective measures(e.g., accelerometer or pedometer), which impacts accurate estimations of PA levels ofChinese youth. Furthermore, although the health of youth is highly emphasized by theChinese government and efforts were made to guarantee the time for exercise, there isa lack of evidence-based PA recommendations specific for Chinese youth. Therefore,the purposes of this thesis were:(1) to objectively assess levels and patterns of PA inChinese youth using accelerometers;(2) to investigate the dose-response relationshipsbetween PA and health indicators including BMI, blood pressure, serum cholesterol,and cardiorespiratory fitness in Chinese youth; and (3) to recommend optimal PAlevel for Chinese youth based on the dose-response relationship between PA andcardiorespiratory fitness. The thesis consists of three studies.Study one (Chapter Two) assessed the PA of3121children and adolescents in11citiesfrom six administrative districts of China using ActiGraph accelerometers.2163participants (boys=1086, girls=1077) provided valid accelerometer data (wearingaccelerometer at least10hours per day for at least two weekday and one weekendday). Results indicated that Chinese youth accrued280.35±83.96min/d of LPA and28.26±17.66min/d of MVPA respectively, and were more active during weekdaysthan weekend days (MVPA=30.16±18.57vs23.56±22.12min/d, P<0.01).5.6%ofparticipants could meet the WHO PA guideline (boys=9.4%, girls=1.9%).Three-way (grade category*gender*BMI category) ANOVA revealed that girlswere less active than boys; whereas no difference existed among obesity, overweightand normal overweight participants.Study two (Chapter Three) investigated the dose-response relationships betweenaccelerometer-measured PA and a cluster of health indicators in Chinese youth.2163participants (boys=1086, girls=1077) who provided valid accelerometer data alsocompleted a series tests for height, weight, waist circumference, blood pressure,resting heart rate, serum cholesterol, and20m shuttle run (used to calculate VO2maxas the indicator of cardiorespiratory fitness). Partial Correlation Analysis revealedweak but significant relationships between MVPA and waist circumferenc (r=-0.167), body fate%(r=-0.123), resting heart rate (r=-0.134), TC (r=-0.156), andVO2max (r=0.296)(all P <0.05). Logistic regression analysis indicated that higherlevels of PA associated with a lower risk of unhealthy serum cholesterol andcardiorespiratory fitness (OR <1, P <0.05). Among all examined health indicators,the strongest association was found between PA and cardiorespiratory fitness.Study three (Chapter Four) determined the optimal PA level for enhancingcardiorespiratory fitness in Chinese youth. The ROC analyses revealed that256.82 min/d of LPA (AUC=0.64, P <0.05) and35.16min/d of MVPA (AUC=0.60, P <0.05) could best differentiate healthy and unhealthy cardiorespiratory fitness of youth.Logistic regression analysis further demonstrated that children and adolescents whosePA levels were above the recommended cut-offs (i.e.257min/d of LPA and35min/dof MVPA) had a lower risk of unhealthy serum cholesterol and cardiorespiratoryfitness (OR <1, P <0.05).In conclusion, objective data indicated that Chinese youth are generally not physicallyactive enough, and lower levels of PA were observed in girls, and during weekenddays. Significant dose-response relationships were observed between PA and anumber of health indicators with cardiorespiratory fitness the most evident. Based onthe relationship between PA and cardiorespiratory fitness, a minimum of256.82min/dof LPA and35.16min/d of MVPA are recommended for Chinese youth to maintain ahealthy cardiorespiratory fitness. The findings of this study will better inform thedevelopment of PA-related policies in schools, the design of PA intervention programs,and help to guide the children and adolescents to effectively prevent health risksthrough appropriate PA and exercise.