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Chapter 9

BPK 143 Chapter Notes - Chapter 9: Bioelectrical Impedance Analysis, Lean Body Mass, Body Fat Percentage


Department
Biomedical Physio & Kines
Course Code
BPK 143
Professor
Tony Leyland
Chapter
9

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BODY COMPOSITION
Chemical composition of the human body by mass
Body composition of a typical man and woman ( 20-24 years old)

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- Getting reliable body composition data is expensive
- Most people do not know what their body composition should be
- There is no ideal percent body fat for every individual
- Pinching the subcutaneous fat (adipose tissue, below the skin) can give some useful information
- Essential fat is essential for life, as it includes fat around nerves, in the brain, and around other essential
organs
- Non-essential fat is fat that acts as an energy store
PERCENT BODY FAT
- The most important consideration when looking at body composition
- Percentage of lean tissue and bone density are also very important
- Its difficult to measure percent body fat
- Another problem with percent body fat estimates occurs when individuals do not exercise in an attempt
to lose body fat
- It may be successful, but often lose a considerable amount of muscle tissue as well
- Percent of body fat may not go down and may even increase when overall body weight done down by
losing both fat and muscle and possibly some bone density
HEIGHT-FOR-WEIGHT TABLES
- Used by insurance companies to predict the future health of potential policyholders
- Its not a measure of body composition
- Height-for-weigh tables show ranges of weights that are associated with the lowest mortality rates
among policyholders
- Show desirable weights rather than average weights
- Convenient to use and work for large population
- Problems with the height-for-weight tables are
1) Height-for-weight tables do not consider body composition, as they don’t distinguish between fat
and other tissues, such as muscle and bone. Body weight doesn’t always reflect obesity, which is a
measure of body fatness. Muscular athletes, for example, may have higher than “normal” weight
and still have low percent body fat.
2) Most of the data in the Metropolitan height-for-weight tables comes from white, middle-class,
American males. This is not a representative sample of the general North American population. The
tables apply to people aged 25 to 59, and therefore don’t cover younger adults or the growing
number of people over 60.
3) Many height-for-weight tables include frame size as a classification variable, but they do not specify
what criteria to use to determine frame size.

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BODY MASS INDEX
-
- Mass in kilograms and height in metres
- Not an assessment of body composition
- Severs a function for epidemiologists and health officials who are tracking population trends in obesity
- Useful because you can easily and cheaply get the BMIs of thousands of objects
- BMI is an excellent tool for some applications, but not for all
- BMI is not as useful for individual assessment as it is for assessing populations
- Some people with high BMI simply because they have a large percentage of muscle and higher bone
density, not higher fat levels
- A very low BMI score can be associated with individuals who do a large volume of weight-bearing
aerobic exercise or can be due to the result of poor eating habits and eating disorder
- You can use the BMI in individual assessment, but only with additional information
- Having a low BMI may not mean you are underweight, might be genetically very lean and have a small
bone structure
SKINFOLD MEASUREMENT
- A special caliper used to measure the thickness of a double layer of skin and subcutaneous fat
- Two ways to use skinfold measurement
1) Add the scores from the various measurement and use the value as an indication of the relative degree
of fatness among subject
2) Use skinfold measurements in equations that predict percent body fat
- There can be considerable error introduced into the estimation of percent body if the person isn’t
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