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Body Composition Techniques

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Title: Advanced Body Composition Techniques Author: Dr. Helen Ward Last modified by: Richard Ward Created Date: 5/20/1997 6:59:06 AM Document presentation format – PowerPoint PPT presentation

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Title: Body Composition Techniques


1
Body Composition Techniques
2
DIRECT ASSESSMENT
  • The only direct methods for body composition
    assessment are dissection or chemical analysis
  • Brussels Cadavre Study
  • 13 female and 12 male cadavers, age range 5594
    years, 12 embalmed and 13 unembalmed
  • After comprehensive anthropometry, each cadaver
    was dissected into skin, adipose tissue, muscle,
    bones, organs and viscera.
  • Volumes and densities of all tissues were
    determined by weighing the tissues underwater.
  • A complete dissection lasted from 10 to 15 h and
    required a team of about 12 people.

3
Indirect or Doubly Indirect estimation of Body
Fat
  • All the techniques used routinely for Body Fat
    estimation are either
  • Indirect
  • body fat is estimated using one or more
    assumptions e.g. Underwater Weighing
  • Doubly Indirect
  • body fat is estimated by predicting the results
    of an Indirect methodology from a related measure
    by regression analysis e.g. Skinfold prediction
    equations

4
Indirect Methods for the Estimation of Body Fat
5
DENSITOMETRY
BODY DENSITY MASS / VOLUME Units gm/ml Any
method that determines the volume of the body is
a densitometric method
6
GOLD STANDARD
  • Densitometry via underwater weighing was the
    gold standard for determination of body fat
    since the 1940s. Since the late 1990s a 4
    compartment method is regarded as the best
    reference method.
  • Body Density can be determined accurately
  • Unfortunately, Body Fat can not because of
    assumptions made in transforming density to Fat

7
DENSITOMETRY
Volumetry by Water Underwater (Hydrostatic)
Weighing Helium Dilution BodPod Whole Body
Plethysmography
8
Predicting Fat from Density
ASSUMPTIONS Body can be divided into two
components Fat Non-Fat (Fat Free) Masses Each
has different, known and constant densities
9
Fat is not Adipose Tissue
  • FAT is ether extractable lipid molecules
  • ADIPOSE TISSUE is a tissue designed to store FAT
    (lipid) in adipocytes. Contains all the
    components of a tissue cellular structures,
    extracellular matrix, water etc. as well as FAT
    (lipid) in the adipocytes. Adipose tissue is
    found subcutaneously and internally

10
SIRI EQUATION
Assumed Densities FAT MASS 0.9 gm/ml NON-FAT
(FAT FREE) MASS 1.1 gm/ml Equation Body Fat
(4.95/Density) - 4.5) x 100
11
Siri Equation Fat (4.95/Density)-4.5) x 100
12
BROZEK EQUATION
Assumptions FAT MASS 0.9 gm/ml LEAN BODY MASS
1.095 gm/ml (some essential lipids in Lean Body
Mass) Equation Fat (4.57/Density)-4.142) x
100
13
DENSITOMETRY Volumetry by Water
Determine body volume by displacing water and
directly measuring the change in water volume
14
DENSITOMETRY Volumetry by Water
 
Where Wa Body Weight in Air Vwater displaced
Measured Volume of water displaced by the Body RV
Residual Volume C Estimate of volume of
entrapped intestinal gas
15
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
16
DENSITOMETRY Underwater Weighing
  • use Archimedes principle to determine body
    volume by calculating weight of water displaced

Small Tank or Open Swimming Pool
17
DENSITOMETRY Underwater Weighing
  • use Archimedes principle to determine body
    volume by calculating weight of water displaced

 
Where Wa Body Weight in Air Ww Body Weight
freely submerged in water Dw Density of water
RV Residual Volume C Estimate of
volume of entrapped intestinal gas
18
DENSITOMETRY 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 or Brozek equation
  • Does not require Residual Volume calculation

19
DENSITOMETRY BODPOD - Whole Body Plethysmography
20
DENSITOMETRY BODPOD - 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 which
    results in bigger increase in pressure with
    injection of known volume of air
  • Advantages over hydrodensitometry
  • subject acceptability
  • precision (reliability not accuracy)
  • Limitations
  • costs 25-30K
  • still assumes constant density of FFM and fat for
    prediction of Body Fat from whole body density

21
DENSITOMETRY BODPOD - Whole Body Plethysmography
22
TOTAL BODY WATER (isotope dilution)
  • Determined by introducing a marker fluid that
    moves freely in body water and is not
    metabolized.
  • Isotopes of water - Deuterium Oxide, tritiated
    water
  • Marker introduced.
  • Following equilibriation period (eg 2 hrs) sample
    body fluid
  • apply conversion formulae to estimate TBW,
  • FAT predicted from TBW
  • Assume a constant for the fraction of water in
    the Fat Free Mass or at least FFM (73.8, 72,3
    etc.)
  • Even if no technical error in Body Water, there
    would still be S.E.E. 3.6 Body Fat associated
    with biological variability

23
K40 - Whole Body Counting
  • K40 emits gamma radiation
  • Using whole body counters the amount of radiation
    emitted can be determined
  • Fat Free Mass (Non-fat Mass) estimated
    Assumptions
  • Constant fraction of K40 in potassium
  • Constant fraction of potassium in non-fat mass
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