Lecture 2 - Measuring Body Composition Flashcards

1
Q

what is the two component model of measuring body composition

A

fat mass + fat free mass

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2
Q

what is the three component model of measuring body composition

A

fat mass + bone mineral content + bone-free fat-free mass

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3
Q

why measure body composition

A
  • health
  • sports performance
  • monitoring growth
  • assessing response to intervention
  • creation of reference values
  • population monitoring
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4
Q

what are the measures of total body composition

A

%fat and % FFM

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5
Q

what is % fat equal to

A

(FM / body weight) x 100

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6
Q

what is % is FFM equal to

A

(FFM / body weight) x 100

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7
Q

what is regional body composition

A

is fat stored primarily in the central or peripheral regions ?

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8
Q

what is the central regional fat distribution known as

A

android

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9
Q

what is the peripheral regional fat distribution known as

A

gynoid

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10
Q

central adiposity increases health risks such as

A
  • type 2 diabetes
  • coronary heart disease
  • hyperlipidaemia
  • cardiovascular disease
  • some cancers
  • arthritis
  • hypertension
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11
Q

central fat is equal to

A

visceral (intra-abdominal) and subcutaneous (under the skin) fat

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12
Q

why is there believed to be increased health risk of visceral fat

A

not known but visceral fat is more metabolically active

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13
Q

when measuring regional fat distribution ideally want to measure

A

measure visceral fat

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14
Q

when using the two component model what must you assume

A

assume composition of FFM is constant - not always true though

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15
Q

what are the 3 categories of two component model approach

A

densitometry

electrical resistance of the body

external measurement

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16
Q

what are the two densitometry methods for the two component approach

A
  1. underwater weighing
  2. air displacement plethysmography
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17
Q

what is the method of electrical resistance of the body for the two component approach

A

bioelectrical impedance analysis

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18
Q

what is the external measurement for the two component approach

A

anthropometry

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19
Q

density =

A

mass / volume

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20
Q

what is the siri equation that has been developed that allow us to calculate % fat from total body density

A

% fat = ((4.940/D) - 4.500) x 100%

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21
Q

what are the assumptions of densitometry

A
  • 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
22
Q

how is underwater weighing used as a two component model technique

A
  • 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
23
Q

what is calculation 1 in underwater weighing

A

body volume = mass air - mass water - residual lung volume - 100 / water density

24
Q

what is calculation 2 in underwater weighing

A

body density = mass air / body volume

25
Q

what is calculation 3 in underwater weighing

A

% body fat = ((4.95 / body density) - 4.50) x 100

26
Q

advantages to underwater weighing

A
  • “gold standard”
  • accurate
  • 2% error
27
Q

what are the limitations to underwater weighing

A
  • density of FFM not necessarily uniform
  • do 4-12 times
  • not suitable for all
  • breathing apparatus to measure lung volume
  • bulky equipment
28
Q

what is an example of air displacement plethysmography

A

BOD POD

29
Q

what is the principle of air displacement plethysmography similar to, but what is different

A

similar to underwater weighing

but calculate displaced air rather than displaced water when person is in and out of chamber

30
Q

how is air displacement calculated

A

there is a known air volume in the chamber and then measure the volume when the person is in there

31
Q

the body conducts electricity through

A

FFM

32
Q

how does bioelectrical impedance analysis work

A

pass weak current through body and measure impedance (resistance + reactance) to current

33
Q

in bioelectrical impedance equations convert resistance and reactance to …

A

estimate FFM

34
Q

what are the two calculations of bioelectrical impedance analysis

A
  1. FFM predicted from total water estimates (FFM = 73% water)
  2. fat mass then derived as difference between body weight and FFM
35
Q

validity of bioelectrical impedance analysis can be impacted by

A
  • hydration status
  • recent physical activity
  • consumption of food / drink
  • menstrual status
  • body position
36
Q

what is good practice of bioelectrical impedance analysis

A
  • 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
37
Q

what are the advantages to bioelectrical analysis

A
  • simple
  • cheap
  • portable
  • suitable for all ages
38
Q

what are the disadvantages to bioelectrical analysis

A
  • need to be fasting
  • control recent activity and hydration status
  • need for appropriate equation for your participants
39
Q

what is the most widely used method of measuring body composition

A

anthropometry

40
Q

what are examples of anthropometry

A

BMI, skin folds, circumferences, breadths

41
Q

how is anthropometry interpreted

A
  • comparing results with reference data : percentiles or standard deviation score (z-score)
  • using cut offs that relate to risk (morbidity, malnutrition)
42
Q

what is anthropometric reference data

A
  • data need to be developed from group representative of healthy population - need to be specific
  • often presented as percentiles
43
Q

what are percentiles

A

describe the position of the measurements in relation to the measurements for a population

44
Q

what are the advantages to anthropometry

A
  • simple
  • safe
  • non invasive
  • cheap
  • portable equipment

commonly used for large studies

45
Q

what are the limitations to anthropometry

A

less accurate do less sensitive to change

46
Q

what are the potential sources of error in anthropometry

A
  • measurement error : intra and inter-examiner
  • variation in tissue composition
  • assumptions may not be valid in disease states of obesity
47
Q

equation needed to work out FM from bioelectrical impedance and TBW

A

FFM = TBW / 0.73

FM = BW - FFM

48
Q

what is s and R equal in the equation to find TBW

A

s = height (its squared)

R = resistance

49
Q

what is male and what is female in the TBW equation

A

male = 1

female = 2

50
Q

cut off for waist circumference in men and women

A

men >102 cm

women > 88cm