**EXAM1- Body Composition Flashcards
body composition
branch of human biology which mainly focuses on the in vivo quantification of body components, the quantitative relationships between components, + component alterations related to various influencing factors
2-compartment model
body is divided into FM + FFM
2 assumptions of 2-compartment model (since fat mass is not directly measured)
-FM has a density of 0.9 g/cm^3
-FFM has a density of 1.1 g/cm^3
FM has a density of ____ g/cm^3
0.9
FFM has a density of ____ g/cm^3
1.1
we typically see more variability in FM/FFM
FFM
example question- if given that someone is 1.02 g/cm^3, be able to identify % body fat
-40% because…
-1 = 50%
-1.1 = 0%
for the assumptions about density of FM/FFM, is it true for all cases
not the case in all genders, race, age, fitness status, + health status
density of water
1 g/cm^3
direct method for measuring/estimating body composition
dissection (in vivo)
indirect methods for measuring/estimating body composition
-skinfolds
-DXA scan
-hydrostatic weighing
-air displacement plethysmography (aka bod pod)
-BIA (bioelectrical impedance analysis, single + multi-frequency)
3 methods of relative fat estimation from correlation with body size
-BW measurement
-BMI
-waist circumference
out of the 3 methods of relative fat estimation from correlation with body size, which tells us the most
waist circumference
-tells us about visceral fat, adiposity
we often see ____ obesity
MASKED
masked obesity
high % body fat but normal BMI
skinfold- direct/indirect measurement of body comp
doubly indirect
what does skinfold directly measure
skinfold thickness
DXA- direct/indirect measurement of body comp
indirect
what does DXA directly measure
density
BIA- direct/indirect measurement of body comp
indirect
what does BIA directly measure
total body water
hydrostatic weighing- direct/indirect measurement of body comp
indirect
what does hydrostatic weighing directly measure
density
bod pod- direct/indirect measurement of body comp
indirect
what does bod pod directly measure
density
obesity
abnormal or excessive fat accumulation that presents a risk to health
associated health risks of obesity
-type 2 diabetes
-CVD
-some cancers
-strokes
-gallstones
-sleep apnea
-osteoarthritis
how do most major health organizations quantify obesity
-BW
-BMI
problem with using BW to quantify obesity
measures total weight which includes fluids, fluctuates a lot throughout the day
(~5% daily)
example of calculating body water fluctuation
200lb man, 65% water
-200lbs x 0.65 = 130ls
-130lbs x 0.05 = 6.75lbs
-so, +/- 6.75lbs variance (13.5lb total)
BMI equation
weight/height^2
units of BMI
kg/m^2
to convert from lbs -> kg
divide by 2.2
to convert from inches -> cm
x2.54
example of BMI calculation
6 feet, 175lbs
-6 ft x 12 inches = 72 inches
-72 inches x 2.54 = 183cm
-183cm/100 = 1.83m
-1.83 x 1.83 = 3.35
-175lbs x .456 = 79.8 kg
-79.8/3.35 = 23.8
what is the most accurate + best measurement of body comp
DXA
if we use BMI…we want to use it in conjunction with
body composition
hydrostatic weighing
very accurate measurement based off of Archimedes principle that the buoyant force which water exerts on an immersed object is equal to the weight of water that the object displaces
what was the OLD gold standard
hydrostatic weighing
is there error in hydrostatic weighing
-there is still an inherent error, due to the major assumption of the 2 compartment model
-the estimation of residual volume of air in the lungs and gastrointestinal tract can also create error
-water temperature also must be accounted for because it slightly changes the density of water
drawbacks of hydrostatic weighing
-high cost
-very high maintenance
standard error of hydrostatic weighing
1.5%
DXA stands for
dual energy x-ray absorptiometry
DXA
originally developed for the diagnosis of osteoporosis + the measurement of bone mineral density through densiometry
-the transmission of photons at two energy levels
what is the GOLD STANDARD
DXA
-msot valid + reliable
drawbacks of DXA
-high costs
-low doses of radiation
standard error of DXA
1.5%
bod pod is also called
air displacement plethysmography
bod pod is similar to what method
hydrostatic weighing
bod pod
measures body volume doing so through changes in air volume
drawbacks of bod pod
-high costs
-calibration
standard error of bod pod
3.5%
BIA stands for
bioelectrical impedance analysis
single frequency BIA
-measures impedance (Z), resistance ( R ), + reactance (X), which are mathematically linked: Z2=R2+X2
-permits estimate of FFM + total body water but cannot determine intra-cellular water
is there a BIA method that measures total body impedance
no
-because current cannot travel through the head
drawbacks of single frequency BIA
-low reliability
-inability to measure dehydrated individuals
-low accuracy
standard error of single frequency BIA
10%
multi-frequency BIA
-uses regression equations from 4 compartment model to adjust fat-mass estimation
-measures impedance (Z), resistance ( R ), + reactance (X), which are mathematically linked: Z2=R2+X2 + use empirical linear regression models to estimate total body water
-uses different frequencies
multi-frequency BIA measurements are made of
-right arm
-left arm
-right leg
-left leg
-trunk
-right side of body
-left side of body
drawbacks of multi-frequency BIA
-accuracy
-cost
standard error of multi-frequency BIA
1.5%
in BIA, fat/muscle has more impedance
fat
waist circumference
horizontal measure at the narrowest part of the torso (above the umbilicus + below the xiphoid process)
-simple, reliable, + correlates well with abdominal fat content irrespective of the BMI
what can waist circumference be used as an indictor of
obesity-related health risk
-because abdominal obesity is the primary issue
