Discussion
adolescence, repetitive behavior
The aim of the present study was to determine the influence of extra 2 hours of physical activity during school on active travel rates among adolescents in 9th grade. During the ScIM intervention, most participants used active travel at baseline and maintained their travel habits throughout the intervention period. While there were differences between the intervention and the control group in terms of baseline active travel rates, the participants who changed their travel habits during the intervention period were similar in both groups (Fig. There may be several possible explanations for our findings. Travel habits are repetitive behavior that can be an integrated part of a daily routine, especially travelling for commuting purposes. One might hypothesize that commuting can be more resistant to external influences. With respect to the ActivityStat hypothesis, we focused on commuting habits in the present study, so a potential compensation effect may have occurred when travelling for other purposes instead. Additionally, since the HBSC instrument captures the typical travel mode, we have investigated the main mode of travel. Smaller changes, for example reducing cycling from five to three days per week, may not be captured in this analysis. With respect to a spillover effect, the trans-contextual model suggests that if autonomous motivation towards an activity occurs in PE during school, the motivation can transfer to similar activities outside of school [Findings from other studies have also indicated that physical activity, is not a determinant for active travel. The SPACE study [Other aspects are important to consider when interpreting the results. For example, previous research indicated that long-lasting interventions over 1 year were more likely support the ActivityStat hypothesis [Overall, the results indicated that the additional curriculum physical activity was in addition to, and not instead of, active travel, which is promising as active travel among adolescence is a key contribution to the total physical activity level [