title: Sociodemographic and behavioral factors associated with physical activity in Brazilian adolescents.
abstract: BACKGROUND
  Physical activity in adolescents is associated with short- and long-term health benefits. Physical activity can occur in various domains and is influenced by a complex network of factors. The aims of this study are 1) to describe the physical activity of Brazilian adolescents in physical education classes, during leisure time, and during active commuting and 2) to investigate the socio-demographic and behavioral factors associated with physical activity.
  
  
  METHODS
  The representative sample included 109,104 Brazilian students in the final year of elementary school from 2,842 schools. The weekly frequency and duration of physical activity were assessed. A variety of socio-demographic and behavioral factors were studied. A multiple Poisson regression analysis was used to test for associations between physical activity and the socio-demographic and behavioral variables.
  
  
  RESULTS
  Most of the students (97.0%) engaged in physical activity in at least one of the domains studied, especially physical education at school (81.7%) and leisure time physical activity (67.5%). However, only 29% of the adolescents reached the recommended level of physical activity. Among the adolescents who reached the minimum recommended time for physical activity, the various domains contributed the following proportions to total physical activity: leisure time physical activity (PR 12.5; 95% CI 11.17-13.97), active commuting (PR 1.63; 95% CI 1.59-1.67), and physical education at school (PR 1.36; 95% CI 1.29-1.44). The weekly frequency of all activities was greater among boys than among girls. Moreover, nearly two-thirds (61.8%) of students spent more than two hours per day engaging in sedentary behaviors; the prevalence of sedentary behaviors was similar between boys and girls (59.0 and 64.5%, respectively).Total level of physical activity, leisure time physical activity, and active commuting were associated with higher nutritional scores.
  
  
  CONCLUSIONS
  Physical activity is important in any health promotion program. Therefore, it is necessary to invest in policies and interagency initiatives that promote all domains and to ensure that the general population helps determine the scope and design of such policies.
authors.affiliation: Universidade de São Paulo - Faculdade de Medicina, Av, Dr, Arnaldo 455, 1° andar,, São Paulo, São Paulo 01246-903, Brazil. lerezende@usp.br.
authors.forename: Leandro Fornias Machado
authors.initials: LF
authors.lastname: de Rezende
authors.forename: Catarina Machado
authors.initials: CM
authors.lastname: Azeredo
authors.forename: Daniela Silva
authors.initials: DS
authors.lastname: Canella
authors.forename: Rafael Moreira
authors.initials: RM
authors.lastname: Claro
authors.forename: Inês Rugani Ribeiro
authors.initials: IR
authors.lastname: de Castro
authors.forename: Renata Bertazzi
authors.initials: RB
authors.lastname: Levy
authors.forename: Olinda do Carmo
authors.initials: Odo C
authors.lastname: Luiz
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D001938:Brazil; D015444:Exercise / Q000523:psychology*; D005260:Female; D015438:Health Behavior; D006801:Humans; D007899:Leisure Activities / Q000523:psychology*; D008019:Life Style; D008297:Male; D010806:Physical Education and Training / Q000379:methods / Q000706:statistics & numerical data; D040242:Risk Reduction Behavior; D012959:Socioeconomic Factors; D014186:Transportation / Q000379:methods / Q000706:statistics & numerical data