Teun Remmers

Afterschool PA and the built environment using GPS, GIS and accelerometers | 141 We found that the distance between children's school and their residence was an important determinant of leisure time PA, bicycling and walking. More specifically, greater home-school distances were related to more bicycling, but less leisure time MVPA and walking. As results from the electronic questionnaire showed that the vast majority of our participants used active transport to get to and from school, greater distances may be related to more bicycling as a replacement of walking during the home-school commute (and vice versa). In addition, greater distances may also reflect the subgroup of participants living in neighbourhoods that may be somewhat further away from facilities (e.g. supermarkets or afterschool activities) (64, 65). This was supported by our finding that lower density of buildings and pedestrian paths was also associated with more cycling. In contrast, we found that higher density of buildings was associated with more minutes of leisure time MVPA. Results may be comparable with results from Rodriguez et al., who found increased MVPA in environments with higher population density (65). In addition, we also found some unexpected associations. For example, the negative association between pedestrian areas and cycling. This may be because these pedestrian areas (in contrast to pedestrian paths) were predominantly present in the central business district, where cycling is usually prohibited. These children also lived somewhat further to their primary school, which in turn may explain increased walking and decreased cycling. Strengths and weaknesses Study strengths are the utilization of GPS devices in order to investigate associations between the objectively assessed built-environment features (using GIS) and domain- specific PA, adjusting for meteorological differences and the nested structure of measurement-days within children, and children within schools. This study also had some weaknesses. Although children were instructed to wear the devices during organized sports programs, children sometimes indicated that they removed the devices because they perceived them as uncomfortable. Although fast developing innovations facilitate application of smaller and thus more comfortable devices combining accelerometry and GPS loggers (e.g. smartphone applications), extensive studies are warranted to validate their performance both in PA- and location assessment. External validity Although we only investigated data within the municipality border from which GIS data was available, findings of this study may be generalizable to other environments with comparable meteorological circumstances, afterschool time segments, population density and residential density. Also as the Netherlands generally have facilities that support cycling (i.e. separate cycling paths), our results may have limited generalizability to environments with less favourable infrastructure for active transport. In addition, findings of this study may be generalizable to samples with comparable distances from children's residences to their primary schools, and similar motives for active transport. As our sample was considered relatively highly educated, this could imply that child- or parental motives regarding leisure time PA may be different from other samples. In addition, time-