Whole body Composition: Measurement Methods Flashcards
what is a limitation of body composition in vivo?
- all in vivo methods for whole body composiiton are estimations
what are 4 reasons we use body composition analysis?
- tracks epidemiological differences and changes
- determine the true efficacy of interventions
- assess health risk
- determine the cause of weight change (e.g in sarcopenia)
what are the three components of body composition
- bone
- fat
- muscle
what are the benefits of skin fold measurements?
- cheap
- easy to use
what percentage of muscle is water?
75%
what percentage of fat is water?
10%
what is component of the body carries the highest percentage of body weight and give its percentage
- muscle
- 41% of body weight
why do females generally have 4 times greater essential fat than males?
for child-bearing and pregnancy
how much body fat does the average young male possess vs females in percentage?
males:
- 12-15%
females:
- 25-28%
what can testosterone do other than increase muscle mass?
It can help increase fat metabolism
what are the percentages of these normal body fat classifications in males AND females:
- unhealthy range (too low)
- acceptable range (lower end)
- acceptable range (higher end)
- unhealthy (too high)
MALES:
- unhealthy (too low): ≤ 5%
- acceptable (lower end): 6-15%
- acceptable (higher end): 16-24%
- unhealthy (too high): ≥ 25%
FEMALES:
- unhealthy (too low): ≤ 8%
- acceptable (lower end): 9-23%
- acceptable range (higher end): 24-31%
- unhealthy (too high): ≥ 32%
Density of what is lower in children than in adults?
density of free-fat mass is lower
what component of free fat mass is higher in children compared to adults?
water content of free fat mass is higher in children compared to adults
what are 3 reasons why muscle mass important in older age
- decreased muscle mass = increase in injury
- glucose disposal to prevent high blood glucose levels, which can lead to things like diabetes
- glycogen storage
in body composition equations/methods, why are there more components in some equations/methods?
because the more components the equation/method uses, the more reliable it is
Give 3 examples of 2 component body composition measurment methods
- skinfolds
- hydrodensitometry
- BIA (bioelectrical impedence analysis)
what 2 things do two component body composition equation methods assume?
Assumes that:
- density of fat is 0.9
- density of fat-free mass is 1.10 kg/L^-1
Give an example of a three-component body composition measurment method/equation
- radio-active isotope tracers
what does the three component body composition equation/method overcome and why?
- As it includes an actual measure of body water, it overcomes errors introduced when a constant proportion of 0.72 Free fat mass is assumed
what are 2 examples of four component body composition equation methods?
- DXA
- CT
what does the four component body composition equation/method overcome and why?
- As the four component body composition method/equation includes an actual measure of body mineral conent, it overcomes errors introduced when a constant proportion of 0.72 Free-fat mass is assumed
what is the chemical division of two component body composition equations and what is the anatomical division?
chemical:
- fat mass (FM) vs ONLY Fat Free Mass (FFM)
Anatomical:
- adipose tissue vs Lean Body Mass (LBM)
what are the chemical and anatomical divisions of multi-component body composition equations
chemical:
- Fat mass vs Water, protein, mineral, and or carbohydrates
Anatomical:
- adipose tissue vs. muscle, skeleton, skin, viscera
what is hydrostatic weighing?
a body composition technique based on archimedes principle of water displacement. The loss of weight in water equals weight of water displaced which yields volume of water displaced at any temperature
what are the 2 equations for hydrostatic weighing?
- Weight in air - weight underwater = weight of water displaced
- Body volume (BV) = (BW-UWW)/0.997 - (RV+0.1)
where:
- BW = body weight in air
- UWW = under water body weight
- RV = litres of gas in lungs
what are 3 advantages hydrostatic weighing
Advantages:
- Used to be considered gold standard
- scientifically sound principle for body volume
- no radiation exposure
what are 5 limitations of hydrostatic weighing
Disadvantages:
- includes measurement of residual lung volume
- Precision of underwater weight
- cost (can be expensive)
- Non-portable
- Not suitable for all subjects
what are 2 assumptions of Hydrostatic weighing
- assumes density of fat and lean mass are constant between individuals
- assumes GI gas volume is constant
outline how an air displacement plethysmography works in 2 steps?
- measures body volume by air displacement by measuring the pressure changes with injection of known volume of air into the closed chamber
- the large body volume displaces air volume in chamber resulting in bigger increase in pressure with injection of known volume of air
what is the advantage of air displacement Plethysmography?
- high validity compared to hydrodensitometry
how does bioelectrical impedance anaylsis measure impedance?
measures impedance (opposition) by body tissues to the flow of a small (** < 1mA**), alternating electrical current of 50kHz
what 2 things is impedance a function of?
function of:
- electrical resistance of tissue
- elecrtrical capacitance (storage) of tissue (reactance)
in bioelectrical impedance analysis, what facilitates electrical flow and what doesn’t and why?
- hydrated fat free body tissues and extracellular water facilitate flow.
- fat does not facilitate flow
this is because of greater electrolyte content of fat-free componenet
in bioelectrical impedance what needs to be the same between each test?
the hydration levels of the subject
what are the 3 advantages of bioelectrical impedance analysis?
- inexpensive
- portable
- quick and non-invasive
what are 3 limitations of bioelectrical impedance analysis?
- low accuracy precision but no worse than hydrodensitometry
- variation between manufacturers/models
- very sensitive to hydration, temp and electrode position
what are 3 assumptions made during bioelectrical impedance analysis
- assumes the body is a series of cylindrical units
- assumes homogeneous body composition
- assumes a large limb contribution
what method is most widely used by COMAP for whole-body composition?
Dual-energy X-ray Absorptiometry (DXA)
what are 5 limitations of a DXA scan?
- expensive specialist equipment
- radiation exposure
- radiation trained staff are required to operate them
- no reference values for certain groups
- excludes populations like pregnant women
what are 5 advantages of a DXA scan?
- accurate
- reliable
- no discomfort for patients
- 4-compartment/component model
- can be used to look at regional/local composition
what 3 steps explain how a DXA scan works on a basic level
- 2 different energy-level x-ray are emitted by the DXA scanner
- lean mass, fat mass and bone mass each reduce/attenuate the X-ray signals in different ways
- computer analyses scan point by point to determine body composition
how does ultrasound work?
It converts electrical energy through a probe into high frequency pulsed sound waves that penetrate the skin surface to the fat-muscle interface
what method of assessment of body composition is most widely used by COMAP for assessment of single muscle architecture?
Ultrasound
what are 5 measurements that are included in anthropometry?
- skinfolds
- height
- weight
- width
- circumferences
what is a disadvantage of skin-folds regarding Fat?
it can only measure subcutaneous fat (fat under the skin) and not visceral fat (around the liver etc)
in skinfolds, how much constant tension does the calipers exert?
10 g/mm^2
what does the sum of skinfolds indicate?
relative fatness of the individual
what are 4 advantages of skin-folds
- inexpensive
- quick
- portable
- larger reference database
what are 3 limitations of skin-folds
- there can be technician error
- skinfold thickness can be affected by factors other than amount of fat
- poorly predicts visceral fat
use 2 steps to explain how a CT scan works
- generates detailed cross-sectional, 2 dimensional radiographic images from many x-rays taken at different angles
- x-rays will pass through tissues of different densities
what 3 things does a CT scan provide quantitive information on?
Provides quantitive information on:
- total tissue area
- total fat and muscle area
- thickness and volume of tissues within an organ
what is the 2 disadvantages of CT scan?
- high radiation exposure
- expensive
what are the 2 advantages of CT scans
- highly accurate
- can be diagnostic
outline 2 steps of how MRI works
- electromagnetic radiation (NON-IONSING) in strong magnetic field exites hydrogen nuclei of body’s water and lipid molecules
- these nuclei then project detectable signal to visually represent various body tissues
what does MRI provide quantitative information on?
provides quantitative information on total and subcutaneous adipose tissue
3 advantages of MRI
- doesnt use ionising radiation
- ongoing cost (once the machine is bought) arent extremely expensive
- provides quantitive infomration on total and subcutaneous adipose tissue
1 disadvantage of MRI?
- expensive to initially buy the MRI scanner
