title: Adolescents' physical activity trends over the years: a three-cohort study based on the Health Behaviour in School-aged Children (HBSC) Portuguese survey.
abstract: OBJECTIVE
  Many young people do not practise enough physical activity (PA) to benefit their health. The three-cohort study aimed to investigate the prevalence of PA and understand the trends between 2002 and 2010, using a representative sample of Portuguese adolescents.
  
  
  METHODS
  The participants were 8483 adolescents (4067 boys, 4416 girls) who participated in the Health Behaviour in School-aged Children Portuguese survey in 2002, 2006 and 2010.
  
  
  METHODS
  A questionnaire was used to collect data of PA. Analyses were run separately for boys and girls.
  
  
  RESULTS
  Boys aged 15-17 reported practising 3.5±1.9 times a week in 2002, 3.9±1.9 times a week in 2006 and 3.8±1.9 times a week in 2010, with a significant increase from 2002 to 2006/2010 (p<0.05). PA practice during the past 7 days decreased from 4.2±2.1 to 3.9+1.9 between 2002 and 2006 (p<0.001) and also decreased from 4.4±2.1 to 3.8±1.9 between 2006 and 2010 (p<0.001). Among girls, PA practices during the past 7 days declined significantly from 3.5±1.9 to 2.7±1.7 between 2002 and 2006 (p<0.001), and from 3.3±1.9 to 2.9±1.7 between 2006 and 2010 (p<0.001).
  
  
  CONCLUSIONS
  The study points to age as a factor related to diminished PA participation. The study also revealed that the prevalence of PA has decreased over the years for the same age groups.
authors.affiliation: Projeto Aventura Social, Lisboa, Portugal.|Centro Interdisciplinar de Estudo da Performance Humana, Faculdade de Motricidade Humana, Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Adilson
authors.initials: A
authors.lastname: Marques
authors.affiliation: Centro Interdisciplinar de Estudo da Performance Humana, Faculdade de Motricidade Humana, Universidade de Lisboa, Lisboa, Portugal.|Centro de Malária e Outras Doenças Tropicais (CMDT), Universidade Nova de Lisboa, Lisboa, Portugal.
authors.forename: Margarida
authors.initials: M
authors.lastname: Gaspar de Matos
mesh_terms: D000293:Adolescent; D015331:Cohort Studies; D003625:Data Collection; D005260:Female; D015438:Health Behavior; D006801:Humans; D008297:Male; D009043:Motor Activity; D011174:Portugal / Q000453:epidemiology; D015995:Prevalence; D012737:Sex Factors; D011795:Surveys and Questionnaires
keywords: EPIDEMIOLOGY; PREVENTIVE MEDICINE; SPORTS MEDICINE