Teun Remmers

| 221 The current chapter describes the societal value and relevance of the work presented in this thesis. This will be described in terms of the relevance of study results for specific target groups. Also the dissemination of the results and products presented in this thesis will be described. Relevance of the results presented in this thesis The importance of regular Physical Activity (PA) for children's health and well-being is well understood, both worldwide and in the Netherlands (1). Increased PA is related to various benefits for children's general health and well-being. For example, several studies have indicated that inactivity is directly linked with various detrimental consequences for health and well-being, such as cardiovascular risk factors, bone health, general cognitive functioning, and social capabilities of children (2-5). In addition, PA may also be indirectly beneficial with respect to the primary prevention of overweight and obesity. As inactivity tends to track from childhood to adolescence and even to adulthood (6, 7), promoting PA is a major health promotion target in children. Given the multi-dimensional short- and long term benefits of PA and the increased need for policies informed by evidence-based information, knowledge about how to effectively increase children's PA levels is of interest to multiple stakeholders such as researchers, policy makers at municipalities, health promotion professionals, school teachers, and parents. Accurate and reliable objective measurements of the frequency, intensity, and duration of PA over longer time periods (e.g. using accelerometers) is essential in identifying children that are insufficiently active and is an essential step in understanding how to increase these PA levels (8). In addition, effectively promoting children's PA levels also requires knowledge about determinants of PA. Several conceptual frameworks propose that besides individual-level factors (e.g. motivation, personality traits), PA is influenced by various layers of environmental factors (9). This may be especially relevant to municipalities and designers of public (urban) spaces. The relative influence of these factors however depend on the type of PA performed. For example, while some attributes of the physical environment may act as determinants of active transport, these attributes may be unsuccessful in influencing PA performed at school. This means that increased specificity of the type of PA (i.e. the PA context) is necessary to understand how PA can be influenced (10). The studies presented in this thesis provide indications for determinants of PA at both the individual and environmental level, which may in turn be used to successfully promote PA in various contexts (e.g. outside play, afterschool PA, sports participation, active transport). The innovative techniques presented in chapters 6, 7, 8 and 9 are examples of the possibilities that arise when combining objective PA and environmental data from multiple sources or sensors. Namely, in these chapters, we have combined accelerometer data with registries of weather elements (chapter 6), school's time schedules (chapter 7) and combined GPS and GIS data (chapters 8 and 9). By doing so, relevant additional insights were obtained on determinants of PA in several social- and physical contexts, as