title: Longitudinal physical activity changes in adolescents: Ho Chi Minh City Youth Cohort.
abstract: OBJECTIVE
  This study aimed to describe the 5-yr longitudinal change in moderate-to-vigorous physical activity (MVPA) among urban adolescents in Ho Chi Minh City, Vietnam, and to identify individual, family, and environmental factors associated with changes in MVPA.
  
  
  METHODS
  The Ho Chi Minh City Youth Cohort is a 5-yr longitudinal cohort with systematic random sampling of 759 students (48% boys) from 18 junior high schools in Ho Chi Minh City, conducted from 2004 to 2009. All measures were taken on five separate occassions. MVPA was assessed by self-report and accelerometry. Data were analyzed using multilevel linear regression models with estimation by generalized linear latent and mixed models.
  
  
  RESULTS
  Overall, after adjusting for covariates, students' accelerometer-based MVPA reduced 38% per annum (rate ratio = 0.62, 95% confidence interval (CI) = 0.59-0.64). Boys spent 2.9 times more in MVPA (rate ratio = 2.94, 95% CI = 2.63-3.22) than their female peers. Compared with normal-weight adolescents, overweight and obese adolescents were doing 40% (rate ratio = 0.60, 95% CI = 0.53, 0.67) less MVPA.
  
  
  CONCLUSIONS
  MVPA significantly declined among Vietnamese adolescents with age. This finding is similar to those reported among Western adolescents and suggests that strategies to promote physical activity in adolescents are a priority in Vietnam because economic transitioning potentially increases the risk of adopting unhealthy lifestyle behaviors associated with obesity and chronic diseases.
authors.affiliation: Sydney School of Public Health, Sydney Medical School, The University of Sydney, Sydney, Australia. nguyenhoang_doantrang@yahoo.com
authors.forename: Nguyen Hoang Hanh Doan
authors.initials: NH
authors.lastname: Trang
authors.forename: Tang Kim
authors.initials: TK
authors.lastname: Hong
authors.forename: Hidde P
authors.initials: HP
authors.lastname: VAN DER Ploeg
authors.forename: Louise L
authors.initials: LL
authors.lastname: Hardy
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Kelly
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dibley
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D015444:Exercise; D005260:Female; D015438:Health Behavior; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity; D009765:Obesity; D050177:Overweight; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014744:Vietnam