Lecture 6 - Asessing body composition Flashcards Preview

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Flashcards in Lecture 6 - Asessing body composition Deck (46):
1

why assess body composition

- classify disease risk
- sport performance
- weight management

2

methods of measuring body composition

- BMI, wait circumference, DEXA, bioelectrical impedance, skinfold measurements

3

Body mass index

indrect measure of body fatness (kg/m^2)
- r=0,7 in correlation with hydrostatic weighing

4

BMI classification

- used to ID at risk inidividuals
- possible misclassifications for underweight, overweight and obese status

5

<18.5

underweight `

6

25-29.9

overweight

7

>40

obese class III

8

waist circumference

- often used along with BMI
- indirect assessment of abdominal adiposity and associated with increased risk of disease
- ID waist and use cross-handed position
- arm position
- tester position: stand off to the right side

9

BMI and Waist circumference

- resistance trained clients who have a BMI in the overweight category but a WC below the cutoffs are unlikely to be at increased health risk

10

anthropometry

measurement of the size and proportion of the human body

11

pros of anthropometry

simple, inexpensive and well suited for large epidemiological surveys and clinical purposes; minimal skill and training required

12

common measures of anthropometry

- girth measurements
- widths, breadths and other skeletal measurements

13

3 limitations of skinfold measurements

- client sensitivity to having them measured
- substantial intra and inter-tester variability in thickness
- time requirements for training, practice and accurate administration``

14

% body fat

- relative body fat
- used classification of body fatness

15

%BF of men

- healthy range: teens
- obese: >22-25%

16

%BF of women

- healthy range: twenties
- obese:>35-38%

17

densitometry

- estimates body density by determining ratio of body mass to body volume (BD=BM/BV)

18

two methods of densitometry

1. hydrostatic weighing (hydrodensitometry)
2. air displacement plethysmography (bod pod)

19

hydrostatic weighing

- criterion measure used for development of %BF prediction equations and validation of field measurements
- compares dry land weight to underwater weight (leaner person will weigh more under water)

20

what does hydrostatic weighing measure

body volume --> used with body weight to calculate body density

21

body volume (BV) formula

(dry weight - underwater weight)/density of water - (RV +100mL)

22

Body density (BD) formula

dry weight/ body volume

23

BD into %BF (Siri, 1961)

%BF=(4.95/BD-4.5)x100

24

BD into %BF (Brozek, 1963)

%BF=(4.57/BD-4.142)x100

25

two-component model`

foundation for many techniques to measure %BF

26

formula for two-component model

body mass = fat mass + fat free mass

27

density of fat mass for every person

0.901g/cc

28

density of fat free mass for every person

1.100g/cc

29

3 constant FFM components (individuals differ amount of fat)

water = 73.8%
minerals = 6.8%
protein = 19.4%`

30

FFM density can vary according to....

age, gender, PA leel, ethnicity, water and mineral density, fatmass (try to take this into account with reference body)

31

what is air displacement plethysmography

-bv by air displacement instead of water
- 2 chambers separated by fibreglass wall (front client, back is reference)
- compares volume and pressure of front chaber with reference chamber to determine volume of individual

32

pros of bod pod

- quick (5-10min)
- requires less technician skill
- requires min client cooperation
- reliable (r=0.9-0.96)

33

cons of bod pod

- size restriction due to chamber size
- may be more suitable for clinical settings
- not appropriate with hydrophobic patients
- approved clothing and swim cap
- no beards

34

Dual-energy x-ray absorptiometry (DEXA)

- uses xrays anda 3-component model of assessment (bone mineral mass, bone free lean tissue and fat mass = total body weight)
- attenuation of xrays is dependent on thickness, density and composition of tissues (different xrays strength dep. on bone, muscle, fat)

35

pros of dexa

- gaining recognition
- safe, low radiation
- quick, 20 min
- min client cooperation
- estimates components not obtained by densiometry (eg bone)
- reliable (r>0.95)

36

cons of dexa

- each manufcaturer comes with own model and software version
- may require licensed technician to run scan
- not recommened when pregnant
- sme clients may not fit bed dimensions

37

field methods of body composition assessment

- more practical for estimating body comp compared to lab methods
- more closely follow standardized testing
- common tests: bioelectrical impedance analysis (BIA) or skinfold

38

bioelectrical impedance

- measures resistance to electric current to estimate %BF
- muscle cell 75% water, fat cell 5-13% water
- water reduces desistance and current moves easier (leaner tissue)
- hydration level determines resistance of tissue to flow of electrical current

39

pros of BIA

- fairly inexpensive
- easy to administer and min training
- quick results

40

cons of BIA

- variability (3-8%)
- pre-test guidelines (no eating or drinking within 4 hrs, no exercise within 12 hrs, no alcohol within 48hrs, urinate within 30 min)
- electrical pathway (ankle to hand, ankle to ankle)

41

skifold measurement

- correlated with body density from hydrostatic weighing (r=0.76)
- SKFs indirectly measure thickness of subcutaneous adipose tissue
- common skin fold sites are subscapular, suprailiac, abdominal, chest, arm, thigh, medial calf

42

assumptions of SKF measurements

- good measure of subcuntaneous fat
- fat distribution (subcutaneous vs internal) is similar for all individuals within gender (leaner individuals have higher proportion of internal fat)
- relationship between sum of SKF and body density
- sum of several SKFs can be used to estimate total body fat (1/2 of BF is subcutaneous)

43

SKF procedure

- take measurements on right side
- landmark it accordingly
- caliper perpendicular to fold, 1cm below fingers
- continue to grasp and elevate fold, take reading 3 sec after releasing caliper tension
- rotate thru 1 cycle and repeat
- min of 2 measurements at each site within 0.5mm take mean value

44

pros of SKF

- relatively inexpensive
- easily to admin
- can estimate %BF
- reliable (r=-0.90) with experienced testers

45

cons of SKF

- requires practice
- limited population, overfat, fascia etc
- variability in equations

46

goal setting with body composition assessment

- once %BF is determined, calculations can be completed for fat weight (total weightx %BF), lean weight (total weight - fat weight) and target weight (lean weight/ (100%-desired fat%)/100))