Academic journal article Childhood Obesity

Growth Trajectories of Young Children's Objectively Determined Physical Activity, Sedentary Behavior, and Body Mass Index

Academic journal article Childhood Obesity

Growth Trajectories of Young Children's Objectively Determined Physical Activity, Sedentary Behavior, and Body Mass Index

Article excerpt

Address correspondence to: Zan Gao, PhD, School of Kinesiology, The University of Minnesota, 207 Cooke Hall, 1900 University Avenue SE, Minneapolis, MN 55455, E-mail: gaoz@umn.edu

Introduction

A growing body of evidence has shown that physical activity (PA) and sedentary behaviors independently predict the development of obesity and chronic diseases, such as diabetes, and therefore, should be addressed as separate constructs.1,2 Given that PA is low and sedentary behaviors are high among children and adolescents,3,4 efforts to promote physically active lifestyles and limit time spent in sedentary behaviors have been top priorities among health professionals.4,5 Such initiatives are based upon the notion that PA is beneficial, whereas sedentary behaviors are detrimental for the health of youth, and that these behaviors become habitual and track over time with the potential to significantly impact health during adulthood.2,6-9 Many transitions (i.e., increased peer influence) from childhood to early adolescence influence individuals' PA and sedentary behaviors,10 and consequently, the tracking of these behaviors are likely to vary during this period of transition. To inform effective interventions and policies designed to promote PA and reduce sedentary behavior for achieving optimal health, it is critical to fully understand how these behaviors change from childhood to early adolescence.

In general, boys are more physically active and less sedentary than girls from early adolescence, onward.6,8,11,12 Yet, few studies have targeted children before they progress into early adolescence. Although longitudinal studies have established gender-specific trajectories in PA,6,8,12 few studies have addressed gender differences in trajectories of PA along with sedentary behaviors across time. Also, European researchers have documented that body mass index (BMI) trajectories from adolescence to adulthood were moderate to strong in girls and moderate in boys13--little is known with regard to the longitudinal relationship of BMI trajectories to PA or sedentary behavior trajectories from childhood to early adolescence. Additionally, no longitudinal evidence examining previously identified gender gaps in PA, sedentary behavior, and BMI trajectories are present in the literature. It remains unclear from the existing literature: (1) when gender differences in PA, sedentary behavior, and BMI emerge, (2) whether such differences become larger over time, and (3) whether these change patterns vary by developmental period. Understanding gender differences in behavior changes over time and the relationships of these changes is important in guiding the development of more effective behavioral interventions. In particular, investigating the dynamic relationships among trajectories in PA, sedentary behavior, and BMI will help to better understand the underlying mechanisms of individuals' behavior and may be useful in informing gender-tailored behavioral intervention programs.

Despite increasing research attention over the past decade to the tracking of PA behaviors,14,15 including some recent literature on PA, sedentary behavior, and BMI, during transition from elementary school to middle school,16-18 little is known concerning the dynamic of relationships among trajectories in objectively determined PA, sedentary behavior, and BMI on a yearly basis from childhood to early adolescence. Therefore, this study was designed to help fill the knowledge gap in this area of inquiry. Specifically, the primary aim is to examine trajectories of children's PA, sedentary behavior, and BMI over time across gender. The secondary aim is to examine associations of trajectories in PA and sedentary behavior with BMI trajectories over time. To my knowledge, this is the first study that discerns trajectories in objective PA, sedentary behavior, and BMI in both boys and girls from childhood to early adolescence. …

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