Body Composition

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Body Composition
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What is Body Composition?

• The amounts of water, protein, minerals, and fat
  in the human body
• The science of determining the absolute and
  relative () contributions of these specific
  components
• The GOAL of body composition assessment is to
  obtain absolute or relative body fat values

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Why Measure It?
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What is OVERWEIGHT ??
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What is OVERFAT ??

• Based on body fat
• Men () Women ()
• At Risk lt 5 lt 8
• Below Average 6-14 9-22
• Average 15 23
• Above Average 16-24 24-31
• At Risk gt 25 gt 32

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Assessment of Body Composition

• Techniques
• Hydrostatic Weighing
• Skinfold
• Bioelectrical Impedance Analysis
• DXA
• Circumferences and Diameters
• Air displacement plethysmography
• NIR, CT Scan, MRI...

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Body Composition Models

• Two Component Model
• conceptual model that divides the body in to
• Fat mass Fat-free mass
• math functions (equations) derived from model
• used for hydro, SKFs, Bod Pod, Anthro

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The Compartmental Models of Body Composition
FBM
FBM
FBM
Lean Tissue
LBM
Body Water
Body Water
Model
Fat Free Body Mass
Mineral
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Body Composition Models

• Two component model
• Assumes that body is composed of
• Fat Fat-Free mass (water, protein, minerals)
• Everyones body density lies between

Fat 0.901 g/cc 100
FFM 1.1 g/cc 100
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Two-Component Model

• Assumptions
• 1. The Density of Fat is 0.901 g/cc
• 2. The Density of FFM is 1.10 g/cc
• 3. Densities of Fat and FFM
• same for all individuals
• 4. Proportions of FFM same for all
• 73.8 Water (.9937 g/cc)
• 19.4 Protein (1.34 g/cc)
• 6.8 Mineral (3.0 g/cc)
• 5. Fat mass is what differs between people

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Two-Component Model
73.8 Water (.9937 g/cc)
6.8 Mineral (3.0 g/cc)
19.4 Protein (1.34 g/cc)
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Two-Component Model

• Problems with the assumptions
• Densities change with
• Age, Ethnicity, Level of Fatness, Activity
  Level

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Two-Component Model
BEST for young to middle aged white men
Population specific equations help compensate for
differences!
Multi-component models can help!
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Two-Component Model

• Variations in body water
• contribute most to variations in FFM density
• hydration vs dehydration studies
• affects BF by 1-3
• Variations in skeletal density
• second major source for FFM density variation
• skeletal density is influenced most by.?
• age!!!
• gender and ethnicity also
• important when measuring kids elderly

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Body Composition Laboratory Methods
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Hydrodensiometry

• Behnke, 1942
• Valid, Reliable, and Widely-Used
• considered gold-standard of lab techniques
• SEE 1
• measures body volume (BV)
• calculate body density (Db)
• Precision error
• .0006 g/cc
• Good precision error
• lt .0015 g/cc

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Hydrodensitometry

• Determine body volume
• Archimedes Principle
• weight loss under water is proportional to volume
  of water displaced
• equals body volume
• Correct for
• Air in lungs (RV)
• Air in GI tract
• Density of water

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Hydrodensitometry

• Procedure?
• Measure RV
• can be done in water or out of water
• predicted is not first choice
• can lead to larger errors (3.3 BF)
• SEE 400-500 mL (r .6-.7)
• Precision error measured .00139g/cc

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Hydrodensitometry

• Calculate body volume
• denominator of equation
• 0.1 L gas in GI tract

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Hydrodensitometry

• Determine body density
• Body mass BV
• Calculate BF
• use population specific
• Siri
• Lohman
• Ortiz
• Wagner or Schutte
• or general equation!
• Brozek Keys

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Equations using 2 component model

• Siri equation

BF (495/Db) - 450
these number derived by assuming fat fat-free
mass densities using direct chemical analysis of
cadavers
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Siri equation
BF (495/Db) - 450
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Sources of Error

• Technician
• Improper scale readings
• Wrong equation used
• Improper weighing technique
• error in RV measurement
• Subject
• Fails to reach RV
• Did not adhere to pre-test guidelines
• normally hydrated
• no food or drink (water) 3 hours prior
• empty bladder and bowels
• no vigorous exercise 12-24 hours prior
• 7 days prior to after menstrual cycle

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Hydrostatic Weighing

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autopsy scale
Strain gauges
Analogue signal integration
platform
to computer
chair
Underwater weighing tank
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Air displacement plethysmography

• Bod Pod
• system utilizes the principles of Boyles law
• inverse relationship between pressure and volume
• P1V1 P2V2
• measures volume by changes in pressure
• 2 chambers
• back chamber (reference) subject chamber
• subject chamber calibrated with known volume
• chamber then measured empty

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Air displacement plethysmography

• Bod Pod
• subject enters BodPod
• 2 measurements are made with subject sitting
  still
• difference between empty full chamber.
• body volume!!
• BV empty - BV full BV of subject

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Air displacement plethysmography

• Body density
• calculated in a similar fashion to that of hydro
  
• equations to determine BF are also similar
• Research using ADP
• reliable valid method for assessing body comp
• close agreement (1.6 BF) between hydro ADP
• Advantages over hydro
• shorter time to complete each analysis
• no measurement of residual volume
• degree of comfort for the subject.

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Air displacement plethysmography

• Sources of error
• clothing
• thoracic gas volume prediction
• subject movement
• volume calibration
• Advantages over hydro
• shorter time to complete each analysis
• no measurement of residual volume
• degree of comfort for the subject
• little technician skill

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Hydro BodPod

• BF equations
• use specific to gender or ethnicity
• valid for population used to develop equation
• enter body density into these equations
• Siri Lohman
• white men Siri
• white women Lohman
• Brozek Keys can be used for both
• Ortiz or Wagner
• black women men

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DXA

• Dual X-ray Absorptiometry
• gold standard for measuring bone density
• possible alternative for hydro
• takes about 10-20 min
• minimal subject cooperation

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DXA

• Limitations
• doesnt measure soft tissue over bone
• assumes TBW is constant
• table width and height
• skinny not long enough for
  tall people
• gt 25 cm sagittal width
• chest to back
• software from brand to brand

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Body Composition Field Methods
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Skinfold Technique

• Estimate total body fat based on relationships
  between
• Subcutaneous fat
• Internal fat
• Body density (Db)
• SKF equations estimate Db
• calculate BF from density
• Error 3.5
• correlates well with BF from hydro

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Skinfold Method

• Common field method
• Mobile
• Quick
• Inexpensive
• Accurate
• Based on
• two-component Model

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Skinfold Assumptions

• Subcutaneous fat proportional to total fat
• sum of SKF gives estimate of total body fat
• Similar fat distribution
• subcutaneously internally
• within gender
• women store more subcutaneously
• shift to internal as you age
• Inverse relationship
• between sum of SKF body density

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Population Generalized Equations

• All techniques have them
• gt 100 Db equations exist
• Population Specific Equations
• Based on
• gender age
• activity level ethnicity
• level of fatness
• do not estimate accurately in
• individuals from other populations
• overestimate very lean or underestimate obese

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Population Generalized Equations

• Generalized Equations
• applies to a greater range of
• ages (18 - 60 years)
• body fatness (up to 45)
• ethnicity gender
• use on large groups
• Quadratic regression model used
• curvilinear relationship
• less over under estimations

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Relationship Between Db and SKF
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Population Generalized Equations

• Good SEE for equations
• FFM
• lt 2 kg for kids
• lt 2.8 kg for women
• lt 3.5 kg for men
• BF
• lt 3.5 BF
• Db
• lt .008 g/cc

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Skinfold Technique
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Skinfold Technique Guidelines

• Find proper equation for client
• Determine and review sites to be measured
• Follow standardized procedures
• Apply population specific equation to determine
  Db
• Convert Db to BF with population specific
  equation

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Standardized Procedures

• All measurements made on RIGHT SIDE

• Measure, ID mark site

• Grasp SKF with thumb index finger of LEFT hand

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Standardized Procedures

• Take duplicate measures to within 10
• Rotate through sites

• Lift fold 1 cm above site to be measured
• Keep fold elevated while measurement is taken
• Place jaws of calipers perpendicular to the fold.
  
• Take reading 1 to 2 seconds after placement

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SKF formulas

• 3-site formula (page 66)
• men chest, abdomen, thigh
• women tricep, suprailiac, thigh
• 7-site formula (page 66)
• men women
• chest
• midaxillary
• triceps
• subscapular
• abdomen
• suprailliac
• thigh

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SKF Sources of Error

• Technician
• tech skill
• improper site location, bad technique
• major source of error!
• caliper type used
• misreading calipers
• wrong prediction equation
• Subject
• did not adhere to pre-test guidelines
• dehydrated, did exercise, etc.
• fat compressibility

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SKF Sources of Error

• How to lower error in SKF method
• train with experienced tech
• practice!
• 50-100 SKFs (Jackson Pollock, 1985)
• follow standardized procedures
• mark measure sites
• use appropriate equations
• choose good calipers

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Skinfold Summary

• Consistency is key
• Time of day
• Equipment
• Technician
• Hydration exercise status

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Skinfold Summary

• Advantages
• fairly accurate (error 3.5)
• quick
• can assess fat changes in specific areas
• Disadvantages
• high level of technician skill required
• less accurate in
• obese, elderly, extremely lean

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Bioelectrical Impedance Analysis

• Uses low level electrical current
• Passes through body to measure resistance
• Flow of current is directly related to BF
• Fat free mass ? resistance
• high in water and electrolytes
• Fat ? resistance
• low in water and electrolytes
• BIA can predict total body water (TBW)
• from resistance measurement
• FFM can be predicted from TBW

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Bioelectrical Impedance Analysis

• Common field method
• Quick Easy
• Non-Invasive
• Inexpensive
• Mobile
• BIA equations
• usually estimate FFM
• dont use BF from machine
• if you can help it!

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BIA
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Using BIA

• Client Guidelines
• NO.
• food or drink within 4 hours
• no ETOH 48 hours prior
• exercise within 12 hours
• diuretic medications within 7 days (caffeine!)
• females who perceive they are retaining water
• pacemakers or other internal metal devices
• jewelry
• Urinate within 30 minutes of test

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BIA advantages disadvantages

• Advantages
• can be accurate (error 3.5 - 6)
• quick non-invasive
• little tech skill
• test various populations
• good for obese older adults
• Disadvantages
• differences between machines / days
• strict client guidelines
• mysterious equations
• very sensitive to hydration status
• various assumptions associated with BIA

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BIA sources of error

• Instrument
• some better than others!
• calibration
• Subject factors
• hydration status, follow pre-test guidelines,
  etc.
• Tech skill
• electrode placement cleaning site
• low error
• Skin room temperature
• cold will increase resistance
• Wrong prediction equation used

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