body composition Flashcards
components of mass:
fat mass:
- essential fat
- storage fat
fat free mass:
- bone
- lean body mass
–> skeletal muscle
–> organs
–> water (~60-70%)
why assess body composition?
- classify disease risk (type 2 diabetes, hypertension, heart disease, stroke, cancers)
- sport performance (biomechanical advantage?)
- weight management: aid in nutrition& exercise prescription
2 compartment:
fat mass = 15-25%
fat free mass = 75-85%
3 compartment:
fat mass
fat free mass
*total body water
4 compartment:
fat mass
fat free mass
*total body water
*bone mineral density
two-compartment model: advantages/disadvantages
advantages:
- easier to measure?
disadvantages:
- assumes densities of tissues are constant within and between individuals, and the person measured only differs from refernce body in amount of fat
- if true FFM density > 1.10 = %BF is underestimated
- if true FFM density <1.10 = %BF is overestimated
- FFM varies with: age, PA level, ethnicity, gender, amount of body fat
multi-compartment model:
advantages/ disadvantages
advantages:
- doesn’t use “reference body” - takes into account age, gender, ethnicity, PA
- SEE < 1%
5+ compartment models
fat mass
fat free mass
total body water
bone mineral density
mineral content of soft tissue
indirect methods of assessing body composition:
- hydrostatic weighing
- DXA
- BodPod
- BIA*
- skinfolds*
- BMI*
- waist circumference*
*doubly indirect
hydrostatic weighing:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- r = 0.95 - gold standard
- r=0.99 - validated if sample is HOMOGENOUS
assumes:
- air trapped in body is uniform and always 110ml
- client is motionless
- hydration status controlled - high?
- low
- high - discomfort
- low - specialized equipment
hydrostatic weighing:
definition/ basic protocol
- find body density by estimating body volume + BW - Archimedes’ principle
- 7-10 trials, use avg of 3 highest weight
- need to hold breath
archimedes’ principle
upward bouyant force = weight of the water displaced
body density =
body mass/ body volume
siri’s equation for hydrostatic weighing; %BF =
%BF = (495/body density) - 450
BODPOD:
definition/ basic protocol
- find adjusted body volume of individual by comparing volume and pressure of front chamber w reference chamber
- measure raw body volume w air displacement and Boyle’s law
- must account for thoracic gas volume (total air inhaled or exhaled)
Boyle’s Law:
pressure-volume relationship = inverse
P1V1 = P2V2
1 = empty chamber
2 = filled chamber
BODPOD
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- mid?
- r=0.97 compared to hydrostatic wt
- “fair” predictive accuracy
- assumes control of isothermal effects of clothing, hair, body SA - mid?
- test retest reliability = 0.9-0.96
- thoracic gas volume? - high - minimal technical skill
- SEE is ~4%
- low
- low - size restriction, need chamber, approved clothing and skin cap, claustrophobia,
DXA (dual energy xray absorptiometry):
definition/ basic protocol
- 3 compartment model ( total body weight = BM mass + bone free lean tissue + fat mass)
- based on calibrated x-ray beams + dual photo energy (ratios of high vs low x ray energies are? constant b/n individuals)
- “emerging gold standard”
DXA:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- high
- for “healthy, normal weight in children/adults” mostly lol
- r= 0.90 concurrent validity w hydrostatic wt
- accounts for individual variability in BMD - high - but depends
- r= 0.90-0.99 depending on manufacturer
- Cv = 0.8-2.7% - high - as long as subject is accurately positioned (in anatomical position) on DXA
- good - SEE = ~3%BF
- low - low radiation dose BUT can’t use if pregnant
- mid?
- quick, less complicated than hydrostatic wt
- must fit bed dimensions
- expensive
doubly-indirect methods:
- BIA (bioelectrical impedance)
- skinfolds
- BMI
- waist circumference
BIA:
definition/ basic protocol
- low electrical current passed through body, resistance measured by 2+ electrodes indicates total body water = estimate % BF
- 2 - compartment model = hydration fraction is always 73%
- water has low resistance to current (muscle = 73% water, fat = 5-13%)
- assumes body is perfect cylinder (unifrom length and CSA)
BIA:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- yes…
- in healthy, young, euvolemic adults
- 3-8% variability…? - mid?
- r = 0.66 - 0.94 depending on manufacturer..
- Cv from 0.3-2.8%?? - high, espicially w foot-to-foot devices
- good SSE of FFM in heterogenous pop. = 3.5-3.7kg
- low
- easy to use, but machine expensive
BMI:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
why measure waist circumference?
- predictor of visceral fat independent of age, sex, and race (excessive body fat on trunk = higher risk factor for coronary heart disease)
- reduce WC w/ diet+exercise to reduce cardiometabolic risk w/o change in BMI
WC:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- low
- doesn’t depict actual amount of body fat
- body shape is individualized
- most useful when combined w BMI - high
- low = depends on administrator
- low?
- low - but may be uncomfortable
- high
skinfolds:
definition
- estimate total body density based of measures of subcutaneous fat
- jackson pollock equation = validated gold standard
Skinfolds:
1. validity
2. reliability
3. objectivity
4. sensitivity
5. participant burden
6. practicality
- meh
- w normal weight/ lean adults
- concurrent validity w hydrostatic wt r= 0.92
- r = 0.76 compared to hydrostatic wt???
- precision depends on type of callipers used
IF administrator is consistent
- relies on prediction equation**w
BUT assumes
- skin thickness is negligible
- fat distribution is similar b/n people - r= 0.99, but depends on calliper used
- low - dependent on administrator skill
- low?
- SEE ~3.5% is trainined.. but ften greater - low - but may be uncomfortable
6.
- equipment relatively inexpensive
- easy to administer if trained
- not for higher weight/ fat populations
- a bit time consuming, less so than other methods
