title: Longitudinal and secular trends in physical activity and sedentary behavior during adolescence.
abstract: OBJECTIVE
  There is little epidemiologic research on longitudinal and secular trends in weight-related health behaviors throughout the stages of adolescence. In particular, few data are available to assess secular trends in various sedentary behaviors. The objective of this research was to investigate longitudinal and secular trends in physical activity and sedentary behavior in a large, diverse cohort of adolescents.
  
  
  METHODS
  Project EAT-II is a 5-year longitudinal study (N = 2516) that includes 2 cohorts that allow for the observation of longitudinal changes from early to midadolescence (junior high to high school; n = 806; mean baseline age: 12.8 +/- 0.8 years) and mid- to late adolescence (high school to post-high school; n = 1710; mean baseline age: 15.8 +/- 0.8 years). EAT-II also examined secular trends in health behavior from 1999 to 2004 in midadolescence. The main outcome measures of the mixed-model regression analyses used in this research were self-reported weekly hours of moderate to vigorous physical activity, television/video viewing, and leisure-time computer use.
  
  
  RESULTS
  Our findings indicate substantial longitudinal changes in moderate to vigorous physical activity, particularly among girls (decreasing 5.9-4.9 hours/week from early to midadolescence and 5.1-3.5 hours/week from mid- to late adolescence), and leisure-time computer use, particularly among boys (increasing 11.4-15.2 hours/week from early to midadolescence and 10.4-14.2 hours/week from mid- to late adolescence). Secular trends further indicate dramatic increases in midadolescent computer use from 1999 to 2004; girls increased from 8.8 to 11.1 hours/week, and boys increased from 10.4 to 15.2 hours/week.
  
  
  CONCLUSIONS
  These adolescents experienced unfavorable shifts in activity patterns, such as longitudinal decreases in moderate to vigorous physical activity, coupled with longitudinal and secular increases in leisure-time computer use. Developing effective health promotion strategies that address a wide array of changing behavioral patterns will be important in promoting long-term health and active lifestyles among adolescents and young adults.
authors.affiliation: Division of Epidemiology and Community Health, University of Minnesota, 1300 S 2nd St, WBOB Suite 300, Minneapolis, MN 55454-1015, USA. nelson@epi.umn.edu
authors.forename: Melissa C
authors.initials: MC
authors.lastname: Nelson
authors.forename: Dianne
authors.initials: D
authors.lastname: Neumark-Stzainer
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hannan
authors.forename: John R
authors.initials: JR
authors.lastname: Sirard
authors.forename: Mary
authors.initials: M
authors.lastname: Story
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D002648:Child; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity