Teun Remmers

Summary | 205 The evidence-base and importance of regular Physical Activity (PA) for children's health and well-being is becoming increasingly understood, both worldwide and in the Netherlands. PA has direct benefits for general cognitive performance, bone health and social capabilities. PA also has long term indirect health benefits via the primary prevention of overweight and obesity. In addition, children's inactivity tends to track from childhood into adolescence and adulthood. Therefore, it is of great interest and societal relevance to investigate how to effectively promote children's daily PA behavior. Previous studies generally studied PA using either objective measurements (e.g. accelerometers) or questionnaires. The eight studies presented in this thesis address four main objectives: 1) investigating the relationship between objectively measured PA and the subsequent development of (over)weight in children, 2) investigating the influence of individual-level determinants (e.g. psychological determinants and socio-demographical factors) on measurements of children's PA, 3) understanding determinants of children's outside play as reported by their parents, how these determinants interact with each other, and in which way the influence of these determinants develop over time, 4) understanding how objectively measured factors in the physical environment relate to measurements of daily PA patterns in children, and how these PA patterns develop in transition from primary to secondary school. Chapter 1 describes the direct and indirect benefits of regular PA in children and introduces current empirical evidence on determinants of PA at both the individual and environmental level. Subsequently, this chapter presents main challenges in measuring PA and potential determinants in the environment, and addresses potential methodological (and technological) advances regarding how these challenges can be dealt with. Finally, this chapter describes the outline of this thesis and introduces the specific studies that were performed. Chapter 2 describes a study on the relationship between PA and the subsequent development of Body Mass Index of 4-9-year-old children. In this study, we have performed analyses based on existing objective measurements of PA (i.e. accelerometer data) carried out within the KOALA Birth Cohort Study. We found that in heavier boys and girls, an increment of 6.5 minutes of MVPA was associated with a subsequent decrease of 0.03 standard deviation BMI scores. In normal weight boys, an increment in moderate-to- vigorous PA was associated with lower BMI standard deviation score. These findings underline that promoting PA in heavier boys and girls should remain a major long-term health promotion strategy in 4-9-year-old children.