Trajectories of Physical Activity in Montreal Adolescents From Age 12 to 17 Years.

Background: Despite the benefits of physical activity, many Canadian adolescents are inactive and rates of inactivity increase with age. Few studies describe the pattern of change in physical activity as a function of age during adolescence. Methods: Data were drawn from the Nicotine Dependence in Teens Study. The analytic sample included 1206 adolescents who completed a 7-day physical activity recall up to 4 times per year over 5 years. Individual growth models, analyzed using multilevel models for change, were developed separately by sex controlling for season. Results: Physical activity levels through adolescence were best described by a cubic function. Levels increased from age 12 to a peak at approximately age 13.5, decreased to age 16.5, and increased again to age 17. Activity participation was highest in the spring and lowest during fall and winter. Substantial within- and between-subject heterogeneity in the trajectories was evident. Conclusion: Adolescent physical activity follows a complex, curvilinear pattern in both males and females, with considerable variation within- and between-persons. [ABSTRACT FROM AUTHOR]