Prevalence of Insufficient Physical Activity and Associated Factors in Brazilian Adolescents

Background: We aimed to describe levels of physical activity (PA) in adolescents living in southern Brazil and to explore associations between PA levels and demographic, socioeconomic, health-related, and parental variables. A further aim was to test the validity and reliability of the questionnaire used. Methods: We conducted a population-based, cross-sectional study including 857 adolescents selected randomly. Insufficient PA was defined as < 300min/wk of MVPA. PA data collected by questionnaire were compared with pedometer counts and with a longer version of the questionnaire in a subsample of 92 adolescents. Results: Reliability of the questionnaire was good, and its validity in comparison with a longer questionnaire was also satisfactory. In comparison with pedometer data, the questionnaire presented moderate agreement. The prevalence of insufficient PA in the whole sample was 69.8% (95% CI = 66.7-72.9). Boys were more active than girls. The prevalence of insufficient PA increased with age in girls but not in boys. Among boys, those from low socioeconomic levels were more likely to be sedentary. Among girls, paternal PA was directly associated with adolescent activity levels. Conclusions: Urgent strategies aimed at increasing levels of activity of adolescents are necessary in Brazil given the high prevalence of insufficient PA detected in this study. The variables associated with insufficient PA varied between boys and girls.