Advanced Body Composition Techniques

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Advanced Body Composition Techniques Powered By Docstoc
					Body Composition
Techniques
DIRECT ASSESSMENT
   The only direct methods for body composition
    assessment are dissection or chemical analysis
   All other techniques are indirect
   Brussels Cadavre Study
    –   Unique
    –   Limited to dissected masses
    –   Dead Old Belgians
“GOLD STANDARD”
   Densitometry via
    underwater weighing is the
    “gold standard” for
    determination of % body fat
    since the 1940’s
   Body Density can be
    determined accurately
   Unfortunately, % Body Fat
    can not because of
    assumptions made in
    transforming density to %
    Fat
DENSITOMETRY


BODY DENSITY = MASS / VOLUME
Units: gm/ml
DENSITOMETRY


Volumetry
 –   determine body volume by displacing water and directly
     measuring the change in water volume


Underwater                   Weighing
 –   use Archimedes’ principle to determine body volume by
     calculating weight of water displaced
Archimedes (287-212 BC)


 King Heiro of Syracuse summoned him to test the
 composition of a supposedly gold wreath
 If assumed to be an alloy of only Gold and Silver
 he could use the laws of bouyancy to determine
 the fractional composition
 Pure Gold and Silver have constant and different
 densities
Predicting % Fat from Density


ASSUMPTIONS
Body can be divided into two components:
      Fat & Non-Fat Masses
Each has different, known and constant densities
SIRI EQUATION


  FAT MASS            0.9 gm/ml
  NON-FAT MASS        1.1 gm/ml


 % Fat = (4.95/Density)-4.5) x 100
BROZEK EQUATION



  FAT MASS                       0.9 gm/ml
LEAN BODY MASS 1.095 gm/ml
     (some essential lipids in Lean Body Mass)

% Fat = (4.57/Density)-4.142) x 100
                               % FAT vs Body Density

                   100

                   80

                   60

  Siri             40
           % FAT



Equation           20

                    0
                         0.9    0.95   1    1.05    1.1   1.15   1.2
                   -20

                   -40
                                       Density (gm/ml)
Error in Prediction of % Fat


Standard Error of Estimate for % Fat
from Densitometry
S.E.E.      =     2.77% Fat
due to variation in density of fat free mass
Obvious Errors
  ID #    Body Density     % Fat via Siri’s     Sum of 10
                              equation          Skinfolds
   22         1.100               0                 63
   16         1.101              -0.4               74
   24         1.102              -0.8               57
   2          1.103              -1.2               55
   5          1.103              -1.2               97
   9          1.105              -2.0               69
   26         1.105              -2.0               87
   28         1.129              -11.6              64
   25         1.130              -12.0              88


  Table 4.2. Body fat predictions for 9 professional football players (Adams et al., 1982).
Variability of Constants
TOTAL BODY WATER

   Determined by introducing a marker fluid that
    moves freely in body water and is not
    metabolized. (isotope dilution)
   Deuterium Oxide, tritiated water
   % FAT PREDICTED FROM TOTAL BODY
    WATER
    –   Assume 73.8% Water in Fat Free Mass
    –   Even if no technical error in Body Water, there
        would still be S.E.E. = 3.6% Fat associated with
        biological variability
Helium Dilution

   Densitometry
   Volume determined using a sealed chamber into which
    a known volume of Helium is introduced.
   Volume of air in chamber determined from dilution of
    Helium.
   Volume without subject determined (V1)
   Volume with subject determined (V2)
   Body Volume of Subject = V1 – V2
   Density = Mass / Body Volume
   %Fat from Siri equation
K40 - Whole Body Counting

   K40 emits gamma radiation
   Using whole body counters the amount of
    radiation emitted can be determined
   Assumptions:
     – Constant fraction of K40 in potassium
     – Constant fraction of potassium in non-fat
       mass
BODPOD
Whole Body Plethysmography
Whole Body Plethysmography

   Measures body volume by air displacement
    –   actually measures pressure changes with injection
        of known volume of air into closed chamber
   Large body volume displaces air volume in
    chamber
    –   results in bigger increase in pressure with injection
        of known volume of air
BODPOD
Whole Body Plethysmography
Whole Body Plethysmography

   Advantages over hydrodensitometry
     – subject acceptability
     – precision
     – residual lung volume not factor
   Limitations
     – costs: $25-30K
     – still assumes constant density of lean
       and fat for prediction of % Body Fat

				
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