Abstract
OBJECTIVES: Canadian adolescents’ sedentary behaviour (SB) is poorly understood and greatly understudied compared to physical activity (PA). Accumulating evidence suggests that SB poses long-term health risks regardless of PA levels. To design effective interventions that target SB, it is critical to first understand adolescents’ sedentary time (ST) trajectories in a Canadian context. Therefore, we examined longitudinal trajectories of Manitoba students’ ST from 2008 to 2011 and identified associated factors in the context of a province-wide physical education (PE) policy.
METHODS: Secondary schools offering grades 9 through 12 were randomly selected in blocks to represent the urban and rural geography of Manitoba. In each selected school (n = 31), a convenience sample of grade 9 or 10 PE classes was recruited, leading to a final sample of 447 students. To assess ST, participants wore accelerometers on 7 consecutive days at baseline (2008) and during at least one follow-up period (2009, 2010 and 2011).
RESULTS: At baseline, students accumulated an average of 540 minutes/day of ST. Over the course of secondary school, students’ ST trajectories remained stable. Females compared to males had a slightly higher rate of decline in ST (p = 0.035), adjusting for socio-demographic variables. ST trajectories were not associated with baseline PA, body mass index and school neighbourhood socio-economic status.
CONCLUSION: Adolescent ST remained high throughout secondary school. SB may be well established by early adolescence and track through late adolescence. Our findings suggest the potential need for additional interventions to reduce SB before and over the course of secondary school.
Key Words: Sedentary time, linear growth model, longitudinal analysis
Résumé
OBJECTIFS: Le comportement sédentaire (CS) des adolescents canadiens est mal compris et beaucoup moins étudié que leur activité physique (AP). Les données qui s’accumulent laissent croire que le CS pose des risques à long terme pour la santé, indépendamment des niveaux d’AP. Pour concevoir des interventions efficaces qui ciblent le CS, il est indispensable de comprendre d’abord les trajectoires du temps de sédentarité (TS) des adolescents dans un contexte canadien. C’est pourquoi nous avons examiné les trajectoires longitudinales du TS d’élèves du Manitoba de 2008 à 2011 et répertorié les facteurs associés dans le contexte d’une politique d’éducation physique (ÉP) provinciale.
MÉTHODE: Des écoles secondaires offrant des classes de la 9e à la 12e année ont été sélectionnées au hasard en blocs pour représenter la géographie urbaine et rurale du Manitoba. Dans chaque école sélectionnée (n = 31), nous avons recruté un échantillon de commodité de classes d’ÉP de 9e ou de 10e année, ce qui a donné un échantillon final de 447 élèves. Pour l’évaluation du TS, les participants ont porté des accéléromètres pendant 7 jours consécutifs au départ (2008) et durant au moins une période de suivi (2009, 2010 et 2011).
RÉSULTATS: Au départ, les élèves ont accumulé 480 minutes/jour de TS. Durant leurs études secondaires, les trajectoires du TS des élèves sont restées stables. Comparativement aux garçons, les filles ont affiché un taux de diminution du TS légèrement supérieur (p = 0,035), compte tenu des variables sociodémographiques. Les trajectoires du TS n’étaient pas associées à l’AP de départ, à l’indice de masse corporelle, ni au statut socioéconomique du quartier de l’école.
CONCLUSION: Le TS des adolescents est resté élevé durant toutes leurs études secondaires. Le CS pourrait être bien ancré dès le début de l’adolescence et se poursuivre jusqu’à la fin de l’adolescence. Nos constatations indiquent que des interventions supplémentaires pourraient être nécessaires pour réduire le CS avant et durant les études secondaires.
Mots Clés: temps de sédentarité, modèle de croissance linéaire, analyse longitudinale
Footnotes
Source of funding: Financial support for this study was provided by the Canadian Institutes of Health Research Population Health Intervention Research Grant.
Conflict of Interest: None to declare.
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