title: Associations of body size and composition with physical activity in adolescent girls.
abstract: OBJECTIVE
  To examine whether components of body composition (size, fat mass, and fat-free mass) were related to physical activity.
  
  
  METHODS
  A random sample of 60 eligible sixth grade girls at each of 36 schools (six schools per region and six regions in total sample); complete measurements on 1,553 girls. Physical activity was assessed over 6 d in each girl using an accelerometer, and body composition was assessed using a multiple regression equation using body mass index and triceps skinfold. Minutes of moderate-to-vigorous and vigorous physical activity were estimated from accelerometer counts per 30 s above threshold values determined from a previous study.
  
  
  RESULTS
  Significant inverse relationships were found for all measures of body size and composition and all physical activity indices. The combination of fat and fat-free mass expressed as a weight and as an index (divided by height squared) along with race, SES, site, and school were most highly associated with physical activity in multiple regression analysis, accounting for 14-15% of the variance in physical activity. Fat mass was more closely related to moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) than fat-free mass with higher standardized regression coefficients.
  
  
  CONCLUSIONS
  We conclude that both fat mass or fat mass index as well as fat-free mass or fat-free mass index make independent contributions in association with physical activity levels. These indices are recommended for future studies.
authors.affiliation: Department of Physiology and Department of Nutritional Sciences, The University of Arizona, Tucson, AZ 85721, USA. lohman@u.arizona.edu
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Lohman
authors.forename: Kimberly
authors.initials: K
authors.lastname: Ring
authors.forename: Kathryn H
authors.initials: KH
authors.lastname: Schmitz
authors.forename: Margarita S
authors.initials: MS
authors.lastname: Treuth
authors.forename: Mark
authors.initials: M
authors.lastname: Loftin
authors.forename: Song
authors.initials: S
authors.lastname: Yang
authors.forename: Melinda
authors.initials: M
authors.lastname: Sothern
authors.forename: Scott
authors.initials: S
authors.lastname: Going
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000293:Adolescent; D001741:Black or African American; D001823:Body Composition / Q000502:physiology*; D001827:Body Height / Q000502:physiology; D015992:Body Mass Index; D049628:Body Size / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D002648:Child; D005080:Exercise Test; D005260:Female; D006630:Hispanic or Latino; D006801:Humans; D009043:Motor Activity / Q000502:physiology*; D012885:Skinfold Thickness; D012923:Social Class; D044465:White People