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