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Skelatal Muscle in Health and Disease > Whole body composition > Flashcards

Whole body composition Flashcards

1
Q

What are the strengths and limitations of body composition analysis?

A
  • Can track epidemiological differences and changes
  • Determine the true efficacy of interventions
  • Assesses health risk
  • Determines the cause of weight change (sarcopenia)
  • Limitations - All in vivo methods for whole-body composition are estimations
  • relative body fat % error of 3-4%
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2
Q

What is the difference in water and fat composition in the human body?

A
  • Males : water = 62%, Fat = 14%
  • Female : water = 52%, Fat= 25%
  • Muscle has ~75% water , Fat - 10%
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3
Q

What are the sex differences in body composition?

A
  • Four times greater essential fat for femalws relates to child bearing
  • Avg young male possesses begween 12-15% body fat
  • Avg young female possesses between 25-28% of body fat
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4
Q

What are the % body fat classifications in males?

A

low = less than 5%,
normal = 6-24%
too high >25%

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5
Q

What are the % body fat classifications in females?

A

Low = less than 8%
Normal = 9-31%
High = greater than 32%

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6
Q

What are age-associated differences in body composition?

A
  • Density of FFM is lower in children than adults
  • Female density of FFM is lower at each age than males
  • Percentage of FFM that is composed of water is higher in children (Fat free mass)
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7
Q

What are some in vitro methods ( direct assesment) for body composition analysis?

A
  • Anatomical dissection of cadabers
  • Chemical analysis = dissolves body into fat and fat free components
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8
Q

What are some in vivo methods for body composition analysis?

A
  • Whole body:
  • hydrostatic weighing
  • Air displacement
  • Electrical properties e.g. bio-electrical impedance (BIA/0
  • Dual-energy X-ray absorptiometry (DXA/DEXA)

Regional :
- subcutaneous adipose tissue
- Ultrasounf
- Near infra-red tolerance
- CSA:
- Skinfolds + Circumferences
- Computed Tomography
- Magnetic resonance imaging

Estimations : Anthropometry to estimate body composition

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9
Q

What is magnetic resonance imaging?

A
  • Electromagnetic radiation, not ionising radiation, in strong magnetic field excites hydrogen nuclei of body’s water and lipid molecules. Nuclei then project detectable signal to visually represent various body tissues
  • Provides quantitative info on total and subcutaneous adipose tissue
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10
Q

What is hydrostatic weighing

A
  • Based on archimedes principle of water displacement
  • Loss of weight in water = weight of water displaced which yields volume of water displaced at any temp
  • Weight in air - weight underwater = weight of water = displaced
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11
Q

What are some advantages and disadvantages of hydrostatic weighing?

A
  • used to be considered gold standard
  • Scientifcally sound principle for body volume
  • no radiation exposure
    -Disadvantages
  • Assumes density of fat and lean are constant (not true as differences in bone and muscle density)
  • Assumes GI gas volume is constant
    Limitations:
  • measurement of residual lung volume
  • Precision of underwater weight
  • Cost
  • Non-portable
  • Not suitable for all subjects
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12
Q

What is air displacement plethysymography (BODPOD)?

A
  • Measures body volume by air displacement
  • actually measures pressure changes with injection of known volume of air into closed chamber
  • Large body volume displaces air volume in chamber
  • results in bigger increase in air pressure with injection of known volume of air
  • High validity compared to hydrodensitometry
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13
Q

What is bioelectrical impedance analysis (BIA)?

A
  • measures imedpance (opposition) by body tissues to the flow of a small (less than 1mA), alternating electrical current (50 kHz)
  • Impedance is a function of:
  • Electrical resistance of tissue
  • Electrical capacitance (storage) of tissue (Reactance)
  • Hydrated, fat-free body tissues and extracellular water facilitate electrical flow compared to fat tissue because of greater electrolyte content of fat-free component
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14
Q

What is BIA theory?

A
  • The body can be considered to be a series of cylinders
  • Resistance is proportional to the length of the cylinder
  • Resistance is inversely proportional to the CSA
  • Volume = the length of the cylinder times its area
  • Knowing the resistance and the length, one can calculate volume
  • Assuming that the current flows past through the past of least resistance (water), then the volume determined is that of body water
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15
Q

What are the types of BIA ?

A
  • Impedance
  • Sensing electrodes, current electrodes
  • Scale + BIA analyser - metal plate electrodes
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16
Q

What are the advantages and disadvantages of BIA?

A
  • Relatively inexpensive
  • portable
  • Quick and non-invasive

Assumptions:
- the body is a series of cyclindrical units
- assumes the homogenous body composition
- Assumes a large limb contribution

Limitations:
- Low accuracy & precision
- No worse than hydrodensitometry
- Variation between manufactures/models
- Very sensitive to hydration, temp and electrode position

17
Q

What is near infra-red interactance?

A
  • Records optical densities which are linearly related to subcutaneous (and total) body fat when entered into predictive equations
  • Uses tech developed by US dept Agriculture to assess body comp of livestock and lipid content of grains
  • Normally used as a single site measure at the biceps
  • Does not accurately predict human body fat across broad range of body fat levels
18
Q

What is anthropometry?

A

includes measure of :
- skinfolds
- height
- weight
- width
- circumferences

19
Q

What are skinfolds?

A
  • common field method
  • Measures double thickness of skin and subcutaneous fat
  • Relationships among selected skinfold sites and body density
  • Caliper experts constant tensuon of 10g/mm2
  • Sum of skinfold indicates relative fatness of individual
20
Q

What are advantages and disadvantages of skin fold measurements?

A
  • Inexpensive
  • Quick
  • Portable
  • Large ref database
  • Assumptions :
  • predicts non-subcutaneous fat
  • Sites represent avg thickness of all sub fat
  • Compressibility of fat similar between subjects
  • Thickness of skin negligible

Limitations:
- technician error
- skinfold thickness affected by factors other than amount of fat ( hydration, oedema, dermatitis)
- Poorly predicts visceral fat

21
Q

What are single site measurements?

A
  • Tricep skinfold thickness
  • Subscapular skinfold thickness
  • Not for estimating body fat determination
  • for comparing against other reference data

Two site measurements:
- Tricep SF and Subscapular SF is correlated with body fatness in children
- Tricep SF and calf SF is correlated in adults

Multiple site measurements :
- Many sites
- Many equations

22
Q

What are circumferences?

A
  • Uses 3 sites
  • men : right forearm, abdomen, right upper arm or buttocks (27+)
  • Women: abdomen, right thigh, right forearm or right calf(27+)
  • Easy to do
  • Gives pattern of fat distribution
  • Can be used for predicting body fat %
  • LIMITATION: Very limited database
23
Q

What is computed (Axial) tomography?

A
  • Generates detailed cross-sectional, 2 dimensional radiographic images from many x-rays taken at diff angles
  • Passes x-ray beam through tissues of different densities
  • Provides quantitative information on:
  • Total tissue area
  • Total fat and muscle area
  • Thickness and volume of tissues within an organ
  • LIMITATION : High radiation exposure

Skelatal Muscle in Health and Disease (16 decks)

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