View
66
Download
4
Category
Preview:
DESCRIPTION
Isak Body Composition
Citation preview
1
http://www.isakonline.com/
Nikki Brown
Body composition
Components of body composition
(BC):
Major component water
Protein and fat components are
relatively small
Remainder primarily bone and
minerals
Behnkes
Reference
Man/Woman Male
Storage fat 12%
Essential fat 3%
Female
Storage fat 15%
Essential fat 12%
Lean Body Mass
• Contains small % non-specific essential fat
Fat Free Mass
• Represents body mass minus all extractable fat
2
2-compartment model
Total body weight is the sum of two
categories:
Fat mass (all extractable lipids)
Fat-free mass (bone, muscles, organs,
connective tissues, essential fat)
Make a assumption that:
Regression equations developed to
calculate BC from known densities of FM
and FFM and whole body density
Density of FM is 0.90 g.cm3
Density of FFM approx 1.10 g.cm3
3
Body density
Using body density %BF can be estimated using the
Siri formula:
Siri %BF = [(495 / Body Density) -450] * 100
Formulae assume density of FFM to remain constant
Varies with growth, maturation, age, gender, ethnicity,
bone density
± 2% variation in FFM within a homogenous group
Bone density variability
The SD of bone density is approximately ± 0.02g.ml-1
= 2% variation
Some equations are more sensitive than others
Example: if a man has a bone density = 1.070g ml-1
Siri equation calculates %BF as 12.6%
Another equation equally valid calculate %BF as 19.1%
If a person’s bone density > 1.100 g ml-1 their %BF
will be underestimated
Black footballers who combine leanness with high
density appear to have negative %BF!
Methods of BC assessment DIRECT
Chemical dissolution:
Cadaver dissection
INDIRECT
Hydrostatic weighing
Dual-energy x-ray absorptiometry
Air displacement plethysmography
Bioelectrical impedance analysis
Skinfolds and girth measurements
Near infrared interactance
Ultrasound
Computed tomography
Magnetic resonance imaging
4
Levels of Validation
Hydrodensitometry
Mass: easy to measure…get on a scale.
Volume: get in the water! (volume of water displaced = volume of your body)
Archimedes’ principal:
Buoyancy Force (Fb) = Weight of Fluid Displaced
Density of bone and muscles > than water
Fat < dense than water
So a person with more bone + muscle will weigh more in water than a person with less bone + muscle
Higher BD + lower &BF
Density = mass/volume
5
Considerations (UWW)
Water in tank must be completely still
Air in body: lungs and gastrointestinal tract
How to control:
Air in lungs: estimate or measure residual lung volume (direct measurement preferable)
Air in GI tract: not measureable, could be anywhere between 0.1 and 1.5 litres, minimise by fasting
Densities of FFM vary due to race, age, and athletic experience.
Gold-
standard
Air-displacement
plethysmography
Air displaced = Body Volume
High validity compared to hydrostatic weighing
Initial volume of empty chamber measured
Subject enters chamber and small changes in air
pressure measured to determine amount of air person
displaces
Allows estimation of body volume (corrected for RV)
Density = mass/volume
6
Considerations (ADP) Expensive to buy
Needs further validation on athletes
Problems with excess body hair
However.........
Minimal compliance by subject
Does not require high technician skill
More convenient than UWW (3-5 mins)
Any age can be tested from children to
the elderly
Reliability has been shown to be good
Pea Pod
Allows safe, non-invasive
evaluation of babies body
composition
Excellent test-to-test
repeatability
Fast test time (about 7
minutes total test time)
Accommodates most
infant behaviours (crying,
movement)
Dual energy x-ray
absorptiometry
Measures differences in absorption of 2 different low x-ray
energies to estimate the bone mineral content and the soft
tissue composition.
Error is approx < 2% compared to densitometry
However, expensive (>£30000),exposure to radiation
• Has the ability to determine
body composition in defined
regions:
• arms
• legs
• trunk.
7
Bioelectrical Impedance
Measures how the body conducts
electricity
Measures impedance (resistance
to flow)
FFM - good conductor (low imp)
FM – poor conductor (high imp)
Hydration important!!
Greater amount of water and
fluids the easier it is for current to
get from hand to foot (lower
resistance) and vice versa
Considerations (BIA) Cheap and easy to use
Ideally subject should not have:
Exercised for 12 hours
Eaten within previous 5 hours
Drunk coffee in previous 4 hours
Drunk alcohol in previous 24 hours.
Not have consumed large amounts of water prior
to testing
Some medications (e.g.diuretics) will also effect
the test results
Accuracy depends on regression equation used –
population specific
Lack of sensitivity to small changes in composition
Less research on scales/hand-held devices
Skinfold thickness
Common field method –
inexpensive, fast, portable
Measures double thickness
of skin and subcutaneous
fat
Total subcutaneous adipose
tissue mass is represented
by selected skinfold sites
Subcutaneous tissue has a
known relationship with
total body fat
8
Skinfold Assumptions Distribution of subcutaneous and visceral fat similar
for all individuals
Questionable
Sites selected represent average thickness of all subcutaneous fat
Approx 30-50% of total body fat located subcutaneously
Biological variation/age/gender/degree of fatness
Compressibility of fat similar between subjects
Thickness of skin negligible
Exercise /Dehydration/ Edema
Estimating %BF from
skinfolds Usually done by summing skinfolds and applying
them into equation BUT………..
Results vary depending on which skinfolds and
equations are used
>100 equations available
as a way to account for
gender age, ethnicity, etc
Best equations utilise SFs
from arm, trunk and leg to
detect deviations in fat pattern
Equation Results
Thorland et al 1984 5.4%
Sloan 1967 6.3%
Withers et al 1987 7.0%
Forsyth & Sinning 1973 7.2%
Katch & McArdle 1973 7.4%
Wilhmore & Behnke 1967 10.2%
Durnin & Womersley 1974 10.7%
Selecting an equation
Sum of 7 skinfolds (Jackson & Pollock, 1978)
Acurately estimates average %BF of physically
active men and range of sports performers
Prediction error ranges from 2.2 to 2.9%
Highest correlation with hydrodensitometry
Sum of 4 skinfolds (Durnin & Womersley, 1974)
Can also be used with minimal loss of accuracy
Increased feasibility
Important to chose equation that is valid for the
population you are measuring
9
Jackson & Pollock Equations
Durnin & Womersley Equations
(1974)
log∑ = sum of triceps, subscapular,
iliac crest and biceps skinfolds
Move to Sum of Skinfolds
Anthropometry practice has moved towards using
skinfold measurement as a sum of skinfolds (SS)
Forms a simple indicator of fatness
Avoids untebable assumption validations
Normative values are available
Sum can be converted as a percentile to show
relative standing within a population
10
Which techniques to use?
Variety of techniques to appraise body composition
each with own assumptions
Choice of technique depends on a number of factors
Need to consider:
Cost (financial and time)
Technician skill
Subject comfort
Error/accuracy
Overview of techniques
Overview of techniques
Recommended