Teun Remmers

152 | Chapter 9 school environment in the transition to secondary school was associated with less self- reported activity and active transport, but no differences were found on accelerometer measured daily PA (17). This is in line with numerous previous studies that showed a lack of cohesion of results from subjectively-measured versus objectively-measured PA (25). Self-reports may be especially vulnerable to social desirability or recall bias, and may cause increased participant's burden (26, 27). However, recent studies showed that it is feasible to passively gather continuous PA and location data, by combining accelerometers and Global Positioning System (GPS) data (28). When combined with Geographical Information Systems (GIS), which holds extensive data about environmental characteristics, the physical context of specific PA patterns (or sedentary behaviour) can be inferred from the contemporaneously-measured geographical location or travel speed (29-32). For example, the study of Klinker et al. (2014) reported on age and gender differences of PA in the contexts of home, school, transport and leisure, and was also able to identify eleven additional contexts (or subdomains) based on evaluation of time- segments and GPS data (33). Consequently, studies combining accelerometers and GPS loggers may also be valuable to unravel changes in context-specific PA patterns during the transition from primary to secondary school. Consequently, literature suggests that the effect of the transition to secondary school on PA is influenced by two factors: gender and active transport to school (13-17). However, there is insufficient evidence that these factors are indeed related to objective PA patterns, and how these factors relate to the various contexts (or domains) in which children participate. Therefore, the aims for the present study were twofold. First, we aimed to investigate the development of context-specific PA patterns in the transition from primary school towards secondary school using accelerometers, GPS loggers and GIS data. Our secondary aim was to investigate potential moderation of this relationship by gender and difference in home-school distances. Methods Design and participants The present study was embedded in the PHysical Activity in public Space Environments (PHASE-kids) study, which was specifically set up to examine longitudinal relationships between characteristics of the physical environment and children's context-specific PA patterns, in the transitional phase from primary to secondary schools. Children's PA patterns were investigated at two time-points; at baseline (in the last year of primary school) and at follow-up (in the first year of secondary school). Measurements were conducted in the municipality of 's-Hertogenbosch in The Netherlands, which covers around 110 square kilometres flatland, and has approximately 150.000 residents (34) (Figure 1). Population density varies between municipality neighbourhoods (1.8 - 59.0 residents per hectare). Average population density of included neighbourhoods was 19.4 residents per hectare (35). At baseline, we invited 30 primary schools to participate (initial