title: A cross-sectional and longitudinal study of travel by walking before and after school among eighth-grade girls.
abstract: OBJECTIVE
  To examine "travel by walking" (TBW) before and after school among eighth-grade girls.
  
  
  METHODS
  Participants attended 36 middle schools from Arizona, Maryland, Minnesota, Louisiana, California, and South Carolina participating in the Trial of Activity for Adolescent Girls. The cross-sectional sample consisted of 3,076 eighth-grade girls, and the longitudinal sample included 1,017 girls who participated in both sixth and eighth grades. Before- or after-school TBW status was determined from the 3-Day Physical Activity Recall. The main outcomes were body mass index and physical activity, which was measured by accelerometry, estimated for total physical activity (light, moderate, vigorous) and moderate-to-vigorous physical activity (MVPA).
  
  
  RESULTS
  Eighth-grade girls who reported TBW had 4 more minutes (95% confidence interval = 2.1-6.1) of MVPA before and after school than nonwalkers, and 2 more minutes of MVPA (95% confidence interval = 1.1-3.1) on an average weekday. In the longitudinal sample, girls who reported TBW before and after school in both sixth and eighth grades (consistent walkers) accumulated more minutes of MVPA for an average weekday than inconsistent walkers in both sixth (27 ± 2.2 vs. 25 ± 1.9 minutes; p = .03) and eighth (28 ± 2.6 vs. 25 ± 2.3 minutes; p = .003) grades. There were no differences in body mass index by walking status.
  
  
  CONCLUSIONS
  Adolescent girls who reported TBW before and after school accumulated more minutes of MVPA than nonwalkers. Efforts to prevent the decline in walking to school in middle school girls could contribute to their overall physical activity.
authors.affiliation: Department of Epidemiology and Biostatistics, University of Maryland School of Public Health, College Park, Maryland 20742, USA. bsaksvig@umd.edu
authors.forename: Brit I
authors.initials: BI
authors.lastname: Saksvig
authors.forename: Larry S
authors.initials: LS
authors.lastname: Webber
authors.forename: John P
authors.initials: JP
authors.lastname: Elder
authors.forename: Dianne
authors.initials: D
authors.lastname: Ward
authors.forename: Kelly R
authors.initials: KR
authors.lastname: Evenson
authors.forename: Marsha
authors.initials: M
authors.lastname: Dowda
authors.forename: Soo Eun
authors.initials: SE
authors.lastname: Chae
authors.forename: Margarita S
authors.initials: MS
authors.lastname: Treuth
mesh_terms: D061725:Accelerometry; D000293:Adolescent; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000379:methods; D009043:Motor Activity; D012111:Residence Characteristics; D012574:Schools; D012959:Socioeconomic Factors; D013997:Time Factors; D014195:Travel; D014481:United States; D016138:Walking / Q000706:statistics & numerical data*