title: Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm.
abstract: BACKGROUND
  The influence of adiposity on upper-limb bone strength has rarely been studied in children, despite the high incidence of forearm fractures in this population.
  
  
  OBJECTIVE
  The objective was to compare the influence of muscle and fat tissues on bone strength between the upper and lower limbs in prepubertal children.
  
  
  METHODS
  Bone mineral content, total bone cross-sectional area, cortical bone area (CoA), cortical thickness (CoTh) at the radius and tibia (4% and 66%, respectively), trabecular density (TrD), bone strength index (4% sites), cortical density (CoD), stress-strain index, and muscle and fat areas (66% sites) were measured by using peripheral quantitative computed tomography in 427 children (206 boys) aged 7-10 y.
  
  
  RESULTS
  Overweight children (n = 93) had greater values for bone variables (0.3-1.3 SD; P < 0.0001) than did their normal-weight peers, except for CoD 66% and CoTh 4%. The between-group differences were 21-87% greater at the tibia than at the radius. After adjustment for muscle cross-sectional area, TrD 4%, bone mineral content, CoA, and CoTh 66% at the tibia remained greater in overweight children, whereas at the distal radius total bone cross-sectional area and CoTh were smaller in overweight children (P < 0.05). Overweight children had a greater fat-muscle ratio than did normal-weight children, particularly in the forearm (92 +/- 28% compared with 57 +/- 17%). Fat-muscle ratio correlated negatively with all bone variables, except for TrD and CoD, after adjustment for body weight (r = -0.17 to -0.54; P < 0.0001).
  
  
  CONCLUSIONS
  Overweight children had stronger bones than did their normal-weight peers, largely because of greater muscle size. However, the overweight children had a high proportion of fat relative to muscle in the forearm, which is associated with reduced bone strength.
authors.affiliation: Centre for Physical Activity and Nutrition Research, Deakin University, Burwood, Australia. gaele.ducher@deakin.edu.au
authors.forename: Gaele
authors.initials: G
authors.lastname: Ducher
authors.forename: Shona L
authors.initials: SL
authors.lastname: Bass
authors.forename: Geraldine A
authors.initials: GA
authors.lastname: Naughton
authors.forename: Prisca
authors.initials: P
authors.lastname: Eser
authors.forename: Richard D
authors.initials: RD
authors.lastname: Telford
authors.forename: Robin M
authors.initials: RM
authors.lastname: Daly
mesh_terms: D050154:Adiposity; D015519:Bone Density; D002648:Child; D005260:Female; D005542:Forearm / Q000503:physiopathology; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology; D008297:Male; D055595:Mechanical Phenomena; D018482:Muscle, Skeletal / Q000503:physiopathology*; D050177:Overweight / Q000503:physiopathology*; D011884:Radius / Q000503:physiopathology*; D013977:Tibia / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed; D034941:Upper Extremity / Q000503:physiopathology