title: Levels of physical activity that predict optimal bone mass in adolescents: the HELENA study.
abstract: BACKGROUND
  Physical activity is necessary for bone mass development in adolescence. There are few studies quantifying the associations between physical activity and bone mass in adolescents.
  
  
  OBJECTIVE
  To assess the relationship between moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) and bone mass in adolescents.
  
  
  METHODS
  Bone mass was measured by dual-energy X-ray absorptiometry and physical activity by accelerometers in 380 healthy Spanish adolescents (189 boys, aged 12.5-17.5 years) from the HELENA-CSS (2006-2007). Subjects were classified according to the recommended amount of MVPA (<60 minutes or ≥60 minutes of MVPA/day). Receiver operating characteristic curve analysis was applied to calculate the relationship between physical activity and bone mass.
  
  
  RESULTS
  Less than 41 and 45 minutes of MVPA/day are associated with reduced bone mass at the trochanter and femoral neck. More than 78 minutes of MVPA/day is associated with increased bone mineral density (BMD) at the femoral neck. Regarding VPA, more than 28 minutes/day for the hip and intertrochanter and more than 32 minutes/day for the femoral neck are associated with increased BMD.
  
  
  CONCLUSIONS
  The recommended amount of physical activity (minutes/day) seems insufficient to guarantee increased bone mass. With some minutes of VPA/day, bone adaptations could be obtained at different bone sites.
authors.affiliation: GENUD/Growth, Exercise, NUtrition and Development Research Group, School of Health Science, University of Zaragoza, Avenida Domingo Miral s/n, Zaragoza, Spain. lgracia@unizar.es
authors.forename: Luis
authors.initials: L
authors.lastname: Gracia-Marco
authors.forename: Luis A
authors.initials: LA
authors.lastname: Moreno
authors.forename: Francisco B
authors.initials: FB
authors.lastname: Ortega
authors.forename: Francisco
authors.initials: F
authors.lastname: León
authors.forename: Isabelle
authors.initials: I
authors.lastname: Sioen
authors.forename: Anthony
authors.initials: A
authors.lastname: Kafatos
authors.forename: David
authors.initials: D
authors.lastname: Martinez-Gomez
authors.forename: Kurt
authors.initials: K
authors.lastname: Widhalm
authors.forename: Manuel J
authors.initials: MJ
authors.lastname: Castillo
authors.forename: Germán
authors.initials: G
authors.lastname: Vicente-Rodríguez
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000293:Adolescent; D015519:Bone Density / Q000502:physiology*; D002648:Child; D003430:Cross-Sectional Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D005269:Femur; D005272:Femur Neck; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D012372:ROC Curve; D013030:Spain; D013997:Time Factors