title: Use of air displacement plethysmography for estimating body fat in a four-component model.
abstract: OBJECTIVE
  To compare measurements of body density (D(b)) obtained from air displacement plethysmography (AP) and hydrostatic weighing (HW) and to determine the accuracy of substituting D(b) via AP (D(b)-AP) for D(b) via HW (D(b)-HW) in estimating body fatness (%Fat(4C)) and the composition and density of the fat-free mass (Dffm) from a four-component model (fat, mineral, water, and protein).
  
  
  METHODS
  D(b) was measured in 50 young adults using AP and HW. Total body water via deuterium dilution, bone mineral content via dual-energy x-ray absorptiometry, and D(b) were used to estimate %Fat(4C).
  
  
  RESULTS
  D(b)-AP and D(b)-HW were highly correlated (r = 0.89, SEE = 0.008 g x mL(-1)), but D(b)-AP (1.065 +/- 0.003 g x mL(-1)) was significantly higher (P < 0.05) than D(b)-HW (1.058 +/- 0.003 g x mL(-1)), resulting in a mean difference of 2.8%fat. Differences between %Fat(4C-AP) (17.8 +/- 1.2%) and %Fat(4C-HW) (19.3 +/- 1.2%) were significant (P < 0.05), but the SD of the differences (2.3%) was low. When D(b)-AP was used in a four-component model in place of D(b)-HW, the calculated Dffm was significantly higher (1.109 +/- 0.002 vs 1.105 +/- 0.002 g x mL(-1)) based on a higher (P < 0.05) protein fraction (22.0 +/- 0.4% vs 20.6 +/- 0.4%) and lower (P < 0.05) water (71.1 +/- 0.4% vs 72.4 +/- 0.4%) and mineral fractions (7.0 +/- 0.1% vs 7.1 +/- 0.1%).
  
  
  CONCLUSIONS
  AP yields a higher D(b) than HW and may not be a valid method for measuring D(b) or estimating %fat using densitometry. However, due to relatively small bias and low individual error, D(b)-AP is an acceptable substitute for D(b)-HW when estimating %fat with a four-component model in young adults.
authors.affiliation: Exercise Research Laboratory, Department of Health and Performance Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA. mindy.millardstafford@hps.gatech.edu
authors.forename: M L
authors.initials: ML
authors.lastname: Millard-Stafford
authors.forename: M A
authors.initials: MA
authors.lastname: Collins
authors.forename: E M
authors.initials: EM
authors.lastname: Evans
authors.forename: T K
authors.initials: TK
authors.lastname: Snow
authors.forename: K J
authors.initials: KJ
authors.lastname: Cureton
authors.forename: L B
authors.initials: LB
authors.lastname: Rosskopf
mesh_terms: D000273:Adipose Tissue; D000328:Adult; D001823:Body Composition; D001826:Body Fluids; D001835:Body Weight; D003720:Densitometry; D005260:Female; D006801:Humans; D008297:Male; D010991:Plethysmography / Q000379:methods*; D012680:Sensitivity and Specificity