Teun Remmers

General discussion | 177 The primary aim of this thesis was to increase our understanding of the relationship between environmental determinants and PA in childhood and adolescence. The different studies that have been conducted focused on either outside play, afterschool PA, total PA on weekdays and weekends, afterschool active transport, and PA patterns in the transition between primary and secondary school. Environmental determinants have been measured subjectively and objectively. Two studies used parental reports of the perceived environment, while four studies examined the environment objectively using systematic neighborhood audits, meteorological registries, or GPS and GIS methodologies. Additionally, this thesis also aimed to study the relationship between PA and the development of Body Mass Index, and in another study we focused on PA enjoyment as a potential individual-level determinant of PA behavior. After discussing the main findings from the eight studies, this chapter subsequently focuses on methodological- and theoretical considerations. Hereafter, recommendations for both practice and future studies are described. Main Findings Relationship between PA and the Development of Body Mass Index Chapter 2 addresses the first aim of this thesis and describes a prospective longitudinal study on the relationship PA and development of Body Mass Index in 4-9-year-old children of the KOALA Birth Cohort Study. PA levels were studied using accelerometers at ages 5 and 7 years. Height and weight were measured at ages 5, 7, and 9 years and presented as standardized BMI scores, calculated from reference values from the Fourth Dutch Growth study (1). Analyses were stratified for gender and baseline weight status, as increments of PA may have a bigger impact on children who were overweight at baseline. Results showed that in heavier boys and girls, an increment of 6.5 minutes of MVPA with a minimum of three measurement days was associated with a subsequent significant decrease of 0.03 standard deviation BMI scores. In normal weight boys, an increment in MVPA was associated with lower BMI standard deviation scores. These findings underline that promoting MVPA in heavier boys and girls should remain a major health promotion priority in 4-9-year-old children. PA Enjoyment and PA Behavior Chapter 3 addresses this thesis' second aim: investigating individual-level determinants of PA in children. This chapter describes a cross-sectional study on potential moderators of the relationship between PA enjoyment and PA in 9-year-old children. In this study, PA enjoyment was self-reported using the validated 14-item PACES questionnaire (2), while PA was measured using accelerometers. Linear regression models were fitted, and moderation in this relationship was explored for gender, age, BMI, and impulsivity. A significant three-way interaction (i.e. PA enjoyment x gender x impulsivity) was found. This means that in boys, impulsivity strengthened the relationship between PA enjoyment and PA behavior, whereas in girls, impulsivity weakened this relationship. Both gender