title: Objectively assessed associations between physical activity and body composition in middle-school girls: the Trial of Activity for Adolescent Girls.
abstract: Declining levels of physical activity probably contribute to the increasing prevalence of overweight in US youth. In this study, the authors examined cross-sectional and longitudinal associations between physical activity and body composition in sixth- and eighth-grade girls. In 2003, girls were recruited from six US states as part of the Trial of Activity for Adolescent Girls. Physical activity was measured using 6 days of accelerometry, and percentage of body fat was calculated using an age- and ethnicity-specific prediction equation. Sixth-grade girls with an average of 12.8 minutes of moderate-to-vigorous physical activity (MVPA) per day (15th percentile) were 2.3 times (95% confidence interval: 1.52, 3.44) more likely to be overweight than girls with 34.7 minutes of MVPA per day (85th percentile), and their percent body fat was 2.64 percentage points greater (95% confidence interval: 1.79, 3.50). Longitudinal analyses showed that percent body fat increased 0.28 percentage points less in girls with a 6.2-minute increase in MVPA than in girls with a 4.5-minute decrease (85th and 15th percentiles of change). Associations between MVPA in sixth grade and incidence of overweight in eighth grade were not detected. More population-based research using objective physical activity and body composition measurements is needed to make evidence-based physical activity recommendations for US youth.
authors.affiliation: Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. June_stevens@unc.edu
authors.forename: June
authors.initials: J
authors.lastname: Stevens
authors.forename: David M
authors.initials: DM
authors.lastname: Murray
authors.forename: Chris D
authors.initials: CD
authors.lastname: Baggett
authors.forename: John P
authors.initials: JP
authors.lastname: Elder
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Lohman
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Lytle
authors.forename: Russell R
authors.initials: RR
authors.lastname: Pate
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Pratt
authors.forename: Margarita S
authors.initials: MS
authors.lastname: Treuth
authors.forename: Larry S
authors.initials: LS
authors.lastname: Webber
authors.forename: Deborah R
authors.initials: DR
authors.lastname: Young
mesh_terms: D000293:Adolescent; D000886:Anthropometry; D001823:Body Composition; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D009043:Motor Activity; D050177:Overweight; D012044:Regression Analysis; D014481:United States