title: Age and sex differences in physical activity of Portuguese adolescents.
abstract: OBJECTIVE
  This study sought to examine sex- and age-associated variations in physical activity (PA) among Portuguese adolescents aged 10-18 yr.
  
  
  METHODS
  A total of 12,577 males and females at the primary or secondary education level were sampled across four regions of Portugal. PA was assessed by a questionnaire, producing four different indexes: work/school (WSI), sport (SI), leisure time (LI), and total physical activity index (PAI). We examined sex and age differences by using two-way analysis of variance.
  
  
  RESULTS
  Males had higher mean values of PA than did females. In both sexes, mean values for all four PA indexes increased from ages 10 to 16 yr. After age 16, females decreased their mean values, whereas males continued to increase their values (except for LI). In both sexes, the average annual rate of change for the mean values of all four PA indexes correspond to three sensitive age periods (10-13, 13-16, and 16-18 yr). Until age 16, average mean changes for females ranged from +0.7 to +1.6% per year, except for SI in the youngest group (a modest decrease). For males under 16 yr, the pattern was similar, with increases ranging from 0.4 to 1.9% per year. After age 16, females experienced decreases of 1-2.1% per year for the four PA indexes, whereas males showed an increase for three indexes and an average decrease of 1.3% per year for LI.
  
  
  CONCLUSIONS
  These results suggest that it is important to consider sex differences in PA levels among Portuguese adolescents. Unlike their male counterparts, Portuguese females may reduce much of their PA during late adolescence.
authors.affiliation: Faculty of Sports, University of Porto, Porto, Portugal. aseabra@fade.up.pt
authors.forename: André Filipe
authors.initials: AF
authors.lastname: Teixeira e Seabra
authors.forename: José Antonio Ribeiro
authors.initials: JA
authors.lastname: Maia
authors.forename: Denisa M
authors.initials: DM
authors.lastname: Mendonça
authors.forename: Martine
authors.initials: M
authors.lastname: Thomis
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Caspersen
authors.forename: Janet E
authors.initials: JE
authors.lastname: Fulton
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D015438:Health Behavior; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D007899:Leisure Activities; D008297:Male; D009043:Motor Activity; D011174:Portugal; D012574:Schools; D012737:Sex Factors; D011795:Surveys and Questionnaires; D013997:Time Factors; D014937:Work