Lecture 2 - Measuring Body Composition

Question 1

what is the two component model of measuring body composition

Answer 1

fat mass + fat free mass

Question 2

what is the three component model of measuring body composition

Answer 2

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

Question 3

why measure body composition

Answer 3

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

Question 4

what are the measures of total body composition

Answer 4

%fat and % FFM

Question 5

what is % fat equal to

Answer 5

(FM / body weight) x 100

Question 6

what is % is FFM equal to

Answer 6

(FFM / body weight) x 100

Question 7

what is regional body composition

Answer 7

is fat stored primarily in the central or peripheral regions ?

Question 8

what is the central regional fat distribution known as

Answer 8

android

Question 9

what is the peripheral regional fat distribution known as

Answer 9

gynoid

Question 10

central adiposity increases health risks such as

Answer 10

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

Question 11

central fat is equal to

Answer 11

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

Question 12

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

Answer 12

not known but visceral fat is more metabolically active

Question 13

when measuring regional fat distribution ideally want to measure

Answer 13

measure visceral fat

Question 14

when using the two component model what must you assume

Answer 14

assume composition of FFM is constant - not always true though

Question 15

what are the 3 categories of two component model approach

Answer 15

densitometry

electrical resistance of the body

external measurement

Question 16

what are the two densitometry methods for the two component approach

Answer 16

1. underwater weighing
2. air displacement plethysmography

Question 17

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

Answer 17

bioelectrical impedance analysis

Question 18

what is the external measurement for the two component approach

Answer 18

anthropometry

Question 19

density =

Answer 19

mass / volume

Question 20

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

Answer 20

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

Question 21

what are the assumptions of densitometry

Answer 21

• 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

Question 22

how is underwater weighing used as a two component model technique

Answer 22

• 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

Question 23

what is calculation 1 in underwater weighing

Answer 23

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

Question 24

what is calculation 2 in underwater weighing

Answer 24

body density = mass air / body volume

Question 25

what is calculation 3 in underwater weighing

Answer 25

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

Question 26

advantages to underwater weighing

Answer 26

- "gold standard" - accurate - 2% error

Question 27

what are the limitations to underwater weighing

Answer 27

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

Question 28

what is an example of air displacement plethysmography

Answer 28

BOD POD

Question 29

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

Answer 29

similar to underwater weighing but calculate displaced air rather than displaced water when person is in and out of chamber

Question 30

how is air displacement calculated

Answer 30

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

Question 31

the body conducts electricity through

Answer 31

FFM

Question 32

how does bioelectrical impedance analysis work

Answer 32

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

Question 33

in bioelectrical impedance equations convert resistance and reactance to ...

Answer 33

estimate FFM

Question 34

what are the two calculations of bioelectrical impedance analysis

Answer 34

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

Question 35

validity of bioelectrical impedance analysis can be impacted by

Answer 35

- hydration status - recent physical activity - consumption of food / drink - menstrual status - body position

Question 36

what is good practice of bioelectrical impedance analysis

Answer 36

- 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

Question 37

what are the advantages to bioelectrical analysis

Answer 37

- simple - cheap - portable - suitable for all ages

Question 38

what are the disadvantages to bioelectrical analysis

Answer 38

- need to be fasting - control recent activity and hydration status - need for appropriate equation for your participants

Question 39

what is the most widely used method of measuring body composition

Answer 39

anthropometry

Question 40

what are examples of anthropometry

Answer 40

BMI, skin folds, circumferences, breadths

Question 41

how is anthropometry interpreted

Answer 41

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

Question 42

what is anthropometric reference data

Answer 42

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

Question 43

what are percentiles

Answer 43

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

Question 44

what are the advantages to anthropometry

Answer 44

- simple - safe - non invasive - cheap - portable equipment commonly used for large studies

Question 45

what are the limitations to anthropometry

Answer 45

less accurate do less sensitive to change

Question 46

what are the potential sources of error in anthropometry

Answer 46

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

Question 47

equation needed to work out FM from bioelectrical impedance and TBW

Answer 47

FFM = TBW / 0.73 FM = BW - FFM

Question 48

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

Answer 48

s = height (its squared) R = resistance

Question 49

what is male and what is female in the TBW equation

Answer 49

male = 1 female = 2

Question 50

cut off for waist circumference in men and women

Answer 50

men >102 cm women > 88cm