Teun Remmers

General discussion | 179 Meteorological Environments as Determinants of PA First, chapter 6 addresses a non-modifiable potential determinant of children's PA: daily weather elements. In this study, we examined the longitudinal influence of daily weather elements (e.g. rain, temperature) on children's PA patterns across the four seasons of one year, reflecting day-to-day variations within children in South-East Australia. Also, potential differences by age, gender, BMI, and type of day (weekdays versus weekend days) were investigated. Daily meteorological data were obtained from weather station registries that were closest to a child's residential location, and were matched with daily accelerometer measurements. Results showed that temperature and type of day (weekdays) were the strongest determinants of PA, followed by solar radiation and humidity. Associations did not differ by socio-demographic factors or BMI. In addition, a strong curvilinear relationship was found between temperature and MVPA, with optimum PA levels around 20-25 degrees Celsius. As this study showed substantially lower PA levels with higher temperatures, policy makers in Australia should consider providing measures to promote appropriate PA without risking sunburns or overheating on hotter days. In addition, this study discusses the necessity to account for weather elements in future studies, and demonstrates how this can be performed while using objective meteorological data and longitudinal designs. Environmental Determinants of Afterschool PA Chapters 7 and 8 both focus on objective determinants of the physical environment, in relation to objectively measured afterschool PA of 8-12-year-old children. Namely, chapter 7 addresses the quality and quantity of PA opportunities in the school environment, comprising the so-called playability index. Playability was studied by systematically auditing school-environments (defined by an 800-m buffer area) of 21 Dutch primary schools. Not only the location of children's residence, but also concurrent activities such as organized sports participation or daylight might influence whether children are physically active in their school environment. Therefore, we studied the relationship between playability of school environments and accelerometer-measured afterschool PA specifically for categories of children with various home-school distances, and within four afterschool time-segments. Children from schools with higher playability- scores spent more light PA and MVPA directly after school until 6 PM. This relationship was attenuated at later time-segments. In addition, we found that these results were strongest for children that lived within 400-m of their primary school. This relationship was no longer significant in children that lived more than 800-m from their school. These results demonstrate the importance of the quality and quantity of playgrounds in school environments. In addition, these results underline that relationships between attributes of the environment and PA can be elucidated by increasing specificity of time and place. Chapter 8 describes a study on relationship between attributes of the physical environment and children's afterschool PA. Based on information from both Global Positioning Systems (GPS) and Geospatial Information Systems (GIS), this study was able to study specific behavioral contexts of the afterschool time-segment; leisure time, cycling and walking. This was done by excluding all data-points with GPS locations at the