This longitudinal study aimed to verify possible changes in the time spent in sedentary activities occurring as screen-time, educational, cultural, social, and transportation domains in a sample of Brazilian adolescents between 2015 and 2017. It is a longitudinal prospective study with 586 adolescents from 12 to 15 years old at the Baseline (2015) enrolled in 14 public schools from Curitiba, Brazil. The Adolescent Sedentary Activity Questionnaire assessed the time spent in sedentary activities in five domains (recreational screen-time, educational, cultural, social, and transportation). A series of linear random effects regressions analyzed changes in the sedentary time between 2015 and 2017, with p < .05. Overall, 323 adolescents dropped out of the study resulting in a retention rate of 44.9%. The overall sedentary time remained stable from 2015 to 2017 (-3.98 min/day, 95%CI: -15.39; 7.42). The screen-time decreased (-22.22 min/day, 95%CI: -30.30; -14.15), and educational (8.29 min/day, 95% CI: 3.52; 13.06), cultural (3.41 min/day, 95% CI: 0.66; 6.15) and social sedentary activities (8.20 min/day, 95% CI: 2.06; 14.34) increased from 2015 to 2017. Significant reductions in screen-time were evidenced along with increases in time spent on other sedentary activities of educational, cultural, and social nature. KeywordsSedentary behavior, Adolescent health, Longitudinal studies.

Introduction: Motivation is one of the main factors that can influence physical activity practice in youth. Schools are ideal settings to provide opportunities to be active. However, few school-based behavioral change interventions have been designed with curriculum-based contents and evaluated in a real-life setting. The Global Health Program (GHP), implemented among 10,000 students in Québec (Canada), aims to promote long-term behavior change through educational strategies guided by school leaders. Therefore, the aim of the present study was to (i) investigate the association between school leaders’ implication and motivation for physical activity in GHP participants, and (ii) to test whether this association is moderated by physical activity level (active vs. inactive) or number of years of participation in the program.Methods: A cross-sectional study among children and adolescents participating in the GHP was conducted. The data collection was carried out in the Fall 2024 using self-report online questionnaires. Demographic data, motivation for physical activity, perception of school leaders’ implication and physical activity level were collected. Linear regressions analysis with interaction terms to examine potential moderating effect were used.Results: Results showed that among the 658 participants (42% girls, mean ± SD age = 14.5 ± 1.8 years) 29.4% reported being active participants have been involved in GHP for an average of 3.1 ± 2.1 years. There was a positive association between school leaders’ implication and autonomous motivation [β̂ = 0.26; (95%CI 0.138; 0.256)]. However, neither PA level [β̂ = − 0.02, (95%CI −0.142; 0.104)] nor years of participation in GHP [β̂ = − 0.02, (95%CI −0.144; 0.102)] moderated this relationship.Conclusion: Results support the importance of the role of school leaders on students’ motivational quality, regardless of their PA status or exposure length to intervention programs. This insight emphasizes the value of cultivating supportive school environments and leadership practices that consistently promote autonomous motivation, thereby encouraging long-term engagement in physical activity among youth, as fostered by the GHP in Québec (Canada).

Background/Objectives: Physical activity and sedentary behavior are key indicators of youth health, and questionnaires offer a cost-effective method for data collection. This systematic review synthesized evidence on the criterion and convergent validity of self-report questionnaires measuring physical activity and sedentary behavior in children and adolescents aged 5–18 years in school settings. Methods: Searches were conducted in SPORTDiscus, Medline, Scopus, ERIC, Academic Search Complete, Education Source, and the Cochrane Library with no date limits. Included studies compared questionnaire results with established measures and were assessed using the consensus-based standards for the selection of health measurement instruments (COSMIN) checklist. Results: Twenty-two studies covering 16 questionnaires were included; additional outcomes included test–retest reliability, content and construct validity, and psychometric evaluation. Validity correlations ranged from very weak to strong (r = 0.11–0.80; ρ = 0.20–0.87), with Bland–Altman agreement (ρ = 0.56–0.70) and mean absolute percentage error up to 199.6%. Conclusions: Eight questionnaires showed acceptable validity and reliability, though research is needed to strengthen evidence on measurement accuracy.

Background: Children and adolescents represent the population most susceptible to problematic smartphone use. This vulnerability is supported by developmental, behavioral, and epidemiological evidence. Objective: To provide a comprehensive synthesis of current evidence regarding the determinants and factors associated with problematic smartphone use (PSU) among youth. Methods: First, a systematized qualitative literature review was developed, and second, exploratory analyses were conducted using data from the SMARTKids Québec pilot study, which surveyed approximately 250 Canadian students aged 6–17. Main findings: The review shows that psychosocial vulnerabilities and sleep disruption stand out as the most consistent correlates with PSU. The exploratory findings highlight that higher levels of smartphone use were positively correlated with age and symptoms of depression, anxiety, and stress. Conversely, higher smartphone use was linked to poorer academic performance. Implications: The chapter emphasizes the importance of distinguishing between underlying psychosocial determinants and associated behavioral or mental health factors. Ultimately, these insights support the need for a balanced and preventive approach, one that avoids alarmism but acknowledges the potential risks of problematic smartphone use, a multifaceted issue with implications for youth development and well-being.