**EXAM1- Body Composition Flashcards by Tara Track

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

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2-compartment model

body is divided into FM + FFM

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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

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FM has a density of ____ g/cm^3

0.9

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FFM has a density of ____ g/cm^3

1.1

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we typically see more variability in FM/FFM

FFM

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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%

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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

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density of water

1 g/cm^3

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direct method for measuring/estimating body composition

dissection (in vivo)

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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)

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3 methods of relative fat estimation from correlation with body size

-BW measurement
-BMI
-waist circumference

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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

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we often see ____ obesity

MASKED

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masked obesity

high % body fat but normal BMI

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skinfold- direct/indirect measurement of body comp

doubly indirect

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what does skinfold directly measure

skinfold thickness

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DXA- direct/indirect measurement of body comp

indirect

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what does DXA directly measure

density

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BIA- direct/indirect measurement of body comp

indirect

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what does BIA directly measure

total body water

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hydrostatic weighing- direct/indirect measurement of body comp

indirect

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what does hydrostatic weighing directly measure

density

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bod pod- direct/indirect measurement of body comp

indirect

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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