title: Influence of physical activity and skeleton geometry on bone mass at the proximal femur in 10- to 12-year-old children--a longitudinal study.
abstract: Physical activity (PA) have long been identified as a determining factor of the mineralization of the skeleton, particularly in children. Our research supports the hypothesis that the geometry of the pelvis and proximal femur (PF) might moderate the effect of PA in the relative mineralization of the PF subregions.
  
  
  BACKGROUND
  Using a longitudinal observational study with two evaluations and a 1-year follow-up interval, we investigated the influence of PA and skeletal geometry in bone mineral density (BMD) and bone mass distribution at the PF in 96 girls and 81 boys (10-12 years). It is plausible that the geometry of the pelvis-PF structure moderates mechanical forces exerted at the hip and therefore creates different degrees of mineralization among PF subregions.
  
  
  METHODS
  Whole body and left hip dual X-ray absorptiometry scans were used to derive geometric measures of the pelvis-inter-acetabular distance (IAD) and PF abductor lever arm (ALA). BMD was measured at the integral, superolateral (SL), and inferomedial (IM) femoral neck (FN), and at the trochanter (TR). These subregions were used to represent bone mass distribution via three BMD ratios: FN/PF, IM/SL, and TR/PF. PA was measured using accelerometry and a bone-specific PA questionnaire (BPAQ).
  
  
  RESULTS
  A longitudinal data approach revealed BPAQ as a positive predictor for all BMD variables (p < 0.05) except TR BMD in girls and FN BMD in boys. Comparing the most active with the less-active participants, the greatest benefits of PA were observed at the FN of the girls with the lowest IAD (p < 0.001), at the FN of the boys with the highest IAD (p < 0.001) and at the TR of the boys with the lowest ALA (p < 0.01).
  
  
  CONCLUSIONS
  Geometric measures of IAD and ALA seem to moderate the effect of PA role in the relative mineralization of the PF regions. On the other hand, absolute BMD levels appear to be determined by mechanical loading.
authors.affiliation: Exercise and Health Laboratory, Interdisciplinary Centre for the Study of Human Performance, Faculty of Human Kinetics, University of Lisbon, Lisbon, Portugal.
authors.forename: G
authors.initials: G
authors.lastname: Cardadeiro
authors.forename: F
authors.initials: F
authors.lastname: Baptista
authors.forename: N
authors.initials: N
authors.lastname: Rosati
authors.forename: V
authors.initials: V
authors.lastname: Zymbal
authors.forename: K F
authors.initials: KF
authors.lastname: Janz
authors.forename: L B
authors.initials: LB
authors.lastname: Sardinha
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D001823:Body Composition / Q000502:physiology; D015519:Bone Density / Q000502:physiology*; D002648:Child; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology*; D005272:Femur Neck / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D006621:Hip Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D012727:Sex Characteristics