title: Precision of measurement and body size in whole-body air-displacement plethysmography.
abstract: OBJECTIVE
  To investigate methodological and biological precision for air-displacement plethysmography (ADP) across a wide range of body size.
  
  
  METHODS
  Repeated measurements of body volume (BV) and body weight (WT), and derived estimates of density (BD) and indices of fat mass (FM) and fat-free mass (FFM).
  
  
  METHODS
  Sixteen men, aged 22--48 y; 12 women, aged 24--42 y; 13 boys, aged 5--14 y; 17 girls, aged 5--16 y.
  
  
  METHODS
  BV and WT were measured using the Bodpod ADP system from which estimates of BD, FM and FFM were derived. FM and FFM were further adjusted for height to give fat mass index (FMI) and fat-free mass index (FFMI).
  
  
  RESULTS
  ADP is very precise for measuring both BV and BD (between 0.16 and 0.44% of the mean). After removing two outliers from the database, and converting BD to body composition, precision of FMI was <6% in adults and within 8% in children, while precision of FFMI was within 1.5% for both age groups.
  
  
  CONCLUSIONS
  ADP shows good precision for BV and BD across a wide range of body size, subject to biological artefacts. If aberrant values can be identified and rejected, precision of body composition is also good. Aberrant values can be identified by using pairs of ADP procedures, allowing the rejection of data where successive BD values differed by >0.007 kg/l. Precision of FMI obtained using pairs of procedures improves to <4.5% in adults and <5.5% in children.
authors.affiliation: Childhood Nutrition Research Centre, Institute of Child Health, London, UK.
authors.forename: J C
authors.initials: JC
authors.lastname: Wells
authors.forename: N J
authors.initials: NJ
authors.lastname: Fuller
mesh_terms: D000273:Adipose Tissue; D000293:Adolescent; D000328:Adult; D000388:Air; D001823:Body Composition / Q000502:physiology*; D001824:Body Constitution / Q000502:physiology*; D001835:Body Weight; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal; D010993:Plethysmography, Whole Body / Q000379:methods*; D012680:Sensitivity and Specificity