title: Total-body skeletal muscle mass: estimation by a new dual-energy X-ray absorptiometry method.
abstract: BACKGROUND
  Skeletal muscle (SM) is an important body-composition component that remains difficult and impractical to quantify by most investigators outside of specialized research centers. A large proportion of total-body SM is found in the extremities, and a large proportion of extremity lean soft tissue is SM. A strong link should thus exist between appendicular lean soft tissue (ALST) mass and total-body SM mass.
  
  
  OBJECTIVE
  The objective was to develop prediction models linking ALST estimated by dual-energy X-ray absorptiometry (DXA) with total-body SM quantified by multislice magnetic resonance imaging in healthy adults.
  
  
  METHODS
  ALST and total-body SM were evaluated with a cross-sectional design in adults [body mass index (in kg/m(2)) < 35] with an SM-prediction model developed and validated in model-development and model-validation groups, respectively. The model-development and model-validation groups included 321 and 93 ethnically diverse adults, respectively.
  
  
  RESULTS
  ALST alone was highly correlated with total-body SM (model 1: R(2) = 0.96, SEE = 1.63 kg, P < 0.001), although multiple regression analyses showed 2 additional predictor variables: age (model 2: 2-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001) and sex (model 3: 3-variable combined R(2) = 0.96, SEE = 1.58 kg, P < 0.001). All 3 models performed well in the validation group. An SM-prediction model based on the SM-ALST ratio was also developed, although this model had limitations when it was applied across all subjects.
  
  
  CONCLUSIONS
  Total-body SM can be accurately predicted from DXA-estimated ALST, thus affording a practical means of quantifying the large and clinically important SM compartment.
authors.affiliation: Obesity Research Center, St Luke's-Roosevelt Hospital and the Institute of Human Nutrition, Columbia University, College of Physicians and Surgeons, New York, NY 10025, USA.
authors.forename: Jaehee
authors.initials: J
authors.lastname: Kim
authors.forename: ZiMian
authors.initials: Z
authors.lastname: Wang
authors.forename: Steven B
authors.initials: SB
authors.lastname: Heymsfield
authors.forename: Richard N
authors.initials: RN
authors.lastname: Baumgartner
authors.forename: Dympna
authors.initials: D
authors.lastname: Gallagher
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000502:physiology*; D015203:Reproducibility of Results; D017678:Sex Distribution