title: Association of objectively measured physical activity with body components in European adolescents.
abstract: BACKGROUND
  Physical activity (PA) is suggested to contribute to fat loss not only through increasing energy expenditure "per se" but also increasing muscle mass; therefore, it would be interesting to better understand the specific associations of PA with the different body's components such as fat mass and muscle mass. The aim of the present study was to examine the association between objectively measured PA and indices of fat mass and muscle components independently of each other giving, at the same time, gender-specific information in a wide cohort of European adolescents.
  
  
  METHODS
  A cross-sectional study in a school setting was conducted in 2200 (1016 males) adolescents (14.7 ± 1.2 years). Weight, height, skinfold thickness, bioimpedance and PA (accelerometry) were measured. Indices of fat mass (body mass index, % fat mass, sum of skinfolds) and muscular component (assessed as fat-free mass) were calculated. Multiple regression analyses were performed adjusting for several confounders including fat-free mass and fat mass when possible.
  
  
  RESULTS
  Vigorous PA was positively associated with height (p<0.05) in males, whilst, vigorous PA, moderate-vigorous PA and average PA were negatively associated with all the indices of fat mass (all p<0.01) in both genders, except for average PA in relation with body mass index in females. Regarding muscular components, vigorous PA showed positive associations with fat-free mass and muscle mass (all p<0.05) in both genders. Average PA was positively associated with fat-free mass (both p<0.05) in males and females.
  
  
  CONCLUSIONS
  The present study suggests that PA, especially vigorous PA, is negatively associated with indices of fat mass and positively associated with markers of muscle mass, after adjusting for several confounders (including indices of fat mass and muscle mass when possible). Future studies should focus not only on the classical relationship between PA and fat mass, but also on PA and muscular components, analyzing the independent role of both with the different PA intensities.
authors.affiliation: GENUD (Growth, Exercise, Nutrition and Development), Department of Physiotherapy and Nursing, Research Group, Faculty of Health Sciences, University of Zaragoza, Avd, Domingo Miral s/n, CP: 50009, Zaragoza, Spain. davidj@unizar.es.
authors.forename: David
authors.initials: D
authors.lastname: Jiménez-Pavón
authors.forename: Amaya
authors.initials: A
authors.lastname: Fernández-Vázquez
authors.forename: Ute
authors.initials: U
authors.lastname: Alexy
authors.forename: Raquel
authors.initials: R
authors.lastname: Pedrero
authors.forename: Magdalena
authors.initials: M
authors.lastname: Cuenca-García
authors.forename: Angela
authors.initials: A
authors.lastname: Polito
authors.forename: Jérémy
authors.initials: J
authors.lastname: Vanhelst
authors.forename: Yannis
authors.initials: Y
authors.lastname: Manios
authors.forename: Anthony
authors.initials: A
authors.lastname: Kafatos
authors.forename: Dénes
authors.initials: D
authors.lastname: Molnar
authors.forename: Michael
authors.initials: M
authors.lastname: Sjöström
authors.forename: Luis A
authors.initials: LA
authors.lastname: Moreno
mesh_terms: D056044:Actigraphy; D000273:Adipose Tissue; D000293:Adolescent; D000886:Anthropometry; D003430:Cross-Sectional Studies; D005060:Europe; D015444:Exercise / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D009043:Motor Activity / Q000502:physiology*