Teun Remmers

Investigating PA patterns in the transition from primary to secondary school | 151 Introduction Insufficient physical activity (PA) and excessive sedentary behaviour in children have been consistently linked to various detrimental short- and long term consequences for health and general wellbeing; such as overweight and obesity (1), bone health (2), and mental health (3). However, children's PA levels decline from childhood to adolescence (i.e. 8-16- year-old) (4-8). The transition between primary and secondary school is an important phase for PA promotion as changes are likely to occur in children (e.g. biological changes and changes in perception of competence and preferences) (9), their physical environment (e.g. changes in the school environment), their social environment (e.g. classmate changes) and their learning environment (e.g. more homework). In total, four studies have longitudinally investigated this transition using subjective measurements of PA (9-12), and five studies using (partly) objective measurements of PA (13-17). In contrast to the above described studies, four additional longitudinal studies examined PA development in 9-15- year-old children, but have not explicitly investigated the change of schools (7, 18-20). Results from studies investigating the transition from primary to secondary school are mixed. For example, six studies reported a decline in PA between primary and secondary school (7, 9, 12, 17-19), while two studies reported an increase in PA in this transition period (13, 16). In addition, previous longitudinal studies have shown that changes in PA from childhood to adolescence differs between boys and girls (4, 21). However, other studies investigating the transition to secondary school do not suggest such moderation by gender. For example, De Meester et al. (2015) found no significant gender differences in development of weekday pedometer steps and accelerometer measured moderate-to-vigorous PA (MVPA), and Jago (2012) found similar change-scores for boys and girls in a-priori gender- stratified analyses on weekday and weekend MVPA in the transition from primary to secondary school (14, 15). However, the available evidence for potential gender differences in this transitional phase to secondary school is still scarce, and additional longitudinal studies are warranted to unravel gender differences or similarities during this important transitional phase. To be able to interpret changes in PA patterns in the transition to secondary school, information about the context (or domain) in which PA occurs is essential (e.g. home, school or organized sports participation). Most studies measured the PA context by complementing their PA-measurements with self-reported contextual data (e.g. transport mode to school) (13-15, 17). For example, three studies showed an increase in self- reported active transport from primary to secondary school (11, 15, 16), Also, several studies have suggested that change in school environments during the transition from primary to secondary school, may affect children's total PA via changes in active transport (11, 13, 17, 22). A major barrier to transport-related PA in youth is the distance between the home and school location (23, 24). Marks et al. (2015) also showed that a change of