Although physical activity level (PAL) is positively correlated with adolescents' health, many adolescents do not fulfill recommendations for physical activity. This study examines the associations of organized sport and self-organized physical activity, with PAL among adolescents. Participants were 301 adolescents (12–13 year-olds). The adolescents wore accelerometers for 1 week according to international standards, and reported their participation in organized sport and self-organized physical activity in a questionnaire. The results showed that the level of participation in organized sport was positively associated with the adolescents' total PAL, while there was no significant association between time spent in self-organized physical activity and adolescents' daily minutes of moderate and vigorous physical activity. In addition, boys who participated <3 h per week (or not at all) in organized sport stood out with the lowest fulfillment of recommended PAL. Our findings underline the critical importance of getting adolescents, especially boys, to participate in organized sport and not to drop out from organized sport during adolescence.

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Research on physical activity (PA) behavior reveals an overall decrease worldwide from early childhood and throughout adulthood. The ability to illuminate which factors promote activity for whom and in which phase of life, therefore, becomes a key concept in extending our understanding of individuals' physical activity trajectories. Accordingly, this study investigates latent trajectories of objectively measured PA in adolescents (n = 306) over 3 years from ages 13 to 15. Further, it was tested whether eagerness for physical activity, perceived athletic competence, and parental support were associated with the different trajectories of PA. Latent class growth analysis revealed two PA trajectories (trajectory 1: "decrease from very high" and trajectory 2: "steeper decrease from high"). Trajectory 1 had a higher PA level at baseline and less PA decline than trajectory 2. Trajectory 1, "decrease from very high," was associated with higher levels of eagerness for physical activity and perception of competence at all three time points. Furthermore, the effect size of differences between trajectory 1, "decrease from very high," and trajectory 2, "steeper decrease from high," increased from baseline (age 13, seventh grade) to posttest (age 15, ninth grade). This finding indicates a stronger experience of PA as enjoyable, personally relevant, and self-confirming behavior (i.e., "I regard myself as a person who exercises") within the most active adolescents and even stronger as they get older. Consistent with previous research, the PA level declined from seventh to ninth grade. Being more eager for PA and perceiving oneself more as athletically competent is related to higher levels of PA. This highlights the importance of optimizing environmental factors that increase adolescents' experience of eagerness for physical activity and physical athletic competence.

Physical activity (PA) among children is positively correlated to several positive health outcomes. Although school time constitutes an important arena for children’s PA level because it includes all children, research in this area in Nordic countries remains limited. The aim of the present study is to investigate school-time’s contribution to both children’s total PA and fulfilment of health recommendations for PA. In total, 320 seventh-grade children volunteered to participate in the study, of which 291 provided valid accelerometer data and were included in the analyses. The results show that school time accounts for 30.6% and 26%, respectively, of boys’ and girls’ total moderate- and vigorous-PA (MVPA) during the week, and for 45.9% and 36.6%, respectively, of the MVPA that children need to fulfil the health recommendations. In addition, boys achieved significantly more MVPA than girls during school time, and school-time’s contribution to the fulfilment of the health recommendations for PA was significantly greater among boys than girls. The findings indicate that PA in school time possesses an unrealized potential to substantially increase children’s weekly PA. Possible strategies for increasing school-time’s contribution to children’s PA level, in general, and girls’ PA level, in particular, are discussed.

This study investigated the association between perceived parental support and eagerness for physical activity (EPA) among adolescents, and the association between EPA and physical activity. We further examined whether perceived athletic competence (PAC) mediates a presumed association between EPA and physical activity level, when controlling for gender. This study included 320 adolescents (aged 12–13) from 18 schools in two medium-sized Norwegian municipalities. Questionnaires and accelerometers were assessed during spring 2017. Structural equation modeling was applied to examine the associations. Standard regression coefficients are presented. Data demonstrated that perceived parental support was positively associated with EPA (β = 0.52), and eagerness was positively associated with PAC (β = 0.52). Both EPA (β = 0.20) and PAC (β = 0.24) were also positively associated with moderate to vigorous physical activity (MVPA). When mediating the relationship between EPA and MVPA, through PAC, the effect on MVPA increased (from β = 0.20 to β = 0.32). Analysis revealed that 87% of the adolescents fulfilled the national health recommendations for physical activity. This study highlights the relevance of EPA and PAC in studies of physical activity among adolescents, and the impact of perceived parental support for adolescents' EPA and physical activity level.