Lecture 2 - Measuring Body Composition Flashcards
what is the two component model of measuring body composition
fat mass + fat free mass
what is the three component model of measuring body composition
fat mass + bone mineral content + bone-free fat-free mass
why measure body composition
- health
- sports performance
- monitoring growth
- assessing response to intervention
- creation of reference values
- population monitoring
what are the measures of total body composition
%fat and % FFM
what is % fat equal to
(FM / body weight) x 100
what is % is FFM equal to
(FFM / body weight) x 100
what is regional body composition
is fat stored primarily in the central or peripheral regions ?
what is the central regional fat distribution known as
android
what is the peripheral regional fat distribution known as
gynoid
central adiposity increases health risks such as
- type 2 diabetes
- coronary heart disease
- hyperlipidaemia
- cardiovascular disease
- some cancers
- arthritis
- hypertension
central fat is equal to
visceral (intra-abdominal) and subcutaneous (under the skin) fat
why is there believed to be increased health risk of visceral fat
not known but visceral fat is more metabolically active
when measuring regional fat distribution ideally want to measure
measure visceral fat
when using the two component model what must you assume
assume composition of FFM is constant - not always true though
what are the 3 categories of two component model approach
densitometry
electrical resistance of the body
external measurement
what are the two densitometry methods for the two component approach
- underwater weighing
- air displacement plethysmography
what is the method of electrical resistance of the body for the two component approach
bioelectrical impedance analysis
what is the external measurement for the two component approach
anthropometry
density =
mass / volume
what is the siri equation that has been developed that allow us to calculate % fat from total body density
% fat = ((4.940/D) - 4.500) x 100%
what are the assumptions of densitometry
- the density of fat free mass is constant
- the density of fat does not vary among people
- the water content of fat free mass is constant
- the proportion of bone to fat free mass is constant
how is underwater weighing used as a two component model technique
- breathe out as much as possible to get as close to residual lung volume as possible
- then submerged for about 7 seconds
- 4-12 times to get good measurement
what is calculation 1 in underwater weighing
body volume = mass air - mass water - residual lung volume - 100 / water density
what is calculation 2 in underwater weighing
body density = mass air / body volume
what is calculation 3 in underwater weighing
% body fat = ((4.95 / body density) - 4.50) x 100
advantages to underwater weighing
- “gold standard”
- accurate
- 2% error
what are the limitations to underwater weighing
- density of FFM not necessarily uniform
- do 4-12 times
- not suitable for all
- breathing apparatus to measure lung volume
- bulky equipment
what is an example of air displacement plethysmography
BOD POD
what is the principle of air displacement plethysmography similar to, but what is different
similar to underwater weighing
but calculate displaced air rather than displaced water when person is in and out of chamber
how is air displacement calculated
there is a known air volume in the chamber and then measure the volume when the person is in there
the body conducts electricity through
FFM
how does bioelectrical impedance analysis work
pass weak current through body and measure impedance (resistance + reactance) to current
in bioelectrical impedance equations convert resistance and reactance to …
estimate FFM
what are the two calculations of bioelectrical impedance analysis
- FFM predicted from total water estimates (FFM = 73% water)
- fat mass then derived as difference between body weight and FFM
validity of bioelectrical impedance analysis can be impacted by
- hydration status
- recent physical activity
- consumption of food / drink
- menstrual status
- body position
what is good practice of bioelectrical impedance analysis
- avoid alcohol and vigorous exercise 24-48 hours before
- measure >2 hours after eating and within 30 minutes of voiding
- subjects lie down, with limbs not touching body
what are the advantages to bioelectrical analysis
- simple
- cheap
- portable
- suitable for all ages
what are the disadvantages to bioelectrical analysis
- need to be fasting
- control recent activity and hydration status
- need for appropriate equation for your participants
what is the most widely used method of measuring body composition
anthropometry
what are examples of anthropometry
BMI, skin folds, circumferences, breadths
how is anthropometry interpreted
- comparing results with reference data : percentiles or standard deviation score (z-score)
- using cut offs that relate to risk (morbidity, malnutrition)
what is anthropometric reference data
- data need to be developed from group representative of healthy population - need to be specific
- often presented as percentiles
what are percentiles
describe the position of the measurements in relation to the measurements for a population
what are the advantages to anthropometry
- simple
- safe
- non invasive
- cheap
- portable equipment
commonly used for large studies
what are the limitations to anthropometry
less accurate do less sensitive to change
what are the potential sources of error in anthropometry
- measurement error : intra and inter-examiner
- variation in tissue composition
- assumptions may not be valid in disease states of obesity
equation needed to work out FM from bioelectrical impedance and TBW
FFM = TBW / 0.73
FM = BW - FFM
what is s and R equal in the equation to find TBW
s = height (its squared)
R = resistance
what is male and what is female in the TBW equation
male = 1
female = 2
cut off for waist circumference in men and women
men >102 cm
women > 88cm
