Body Composition. Densitometry. The difference in weight in a person in air and after submerging in water can be used to work out volume This works because 1litre of water weighs 1 Kg Density can then be calculated
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The difference in weight in a person in air and after submerging in water can be used to work out volume
This works because 1litre of water weighs 1 Kg
Density can then be calculated
The density is important to help work out the proportion of fat a person has as fat is less dense than muscle.
An example of this calculation is:
Density (g cmֿ³) = 60,000 g (60 kg)/58,000 cm³
= 1.0345 g cmֿ³
% Fat = 495/1.0345 – 450
New method of measuring body density
Bod Pod uses air displacement instead of water to measure body volume
Subject sits in a small chamber (Bod Pod) and body volume is computed by initial vol. of chamber minus vol. with person inside
short measurment time, non-submersion, used by elderly, obese, children etc
very high cost
This is the most widely used methods for estimating body composition and involves measuring the layer of fat under the skin (subcutaneous layer) at specific sites with a skinfold calliper.
Four sites are commonly used
Digital skinfold calipers
Skinfold thickness taken
from the triceps muscle
The sum of the 4 skinfolds is used in a mathematical formula to predict body density and in turn % body fat
Advatages= non-invasive, cheap, portable, quick, accurate once skill is mastered
Disadvantages = errors with measurer skill, does not take into account unusual fat distribution, difficult in the very obese and the very lean
BIA is based on the principle that the FFM (which is about 73% salty water) offers very little resistance to the flow of a small electric current whereas the FM (which is an insulator) conducts very little of the current.
Therefore, measuring the impedance of the body to the flow of the applied electric current can give an estimate of the lean/fat ratio in the body.
Advantages of BIA:
Requires little or no technical skill by the operator
Takes less that a minute to perform
Unit is easily transportable
Only requires removal of a sock (unlike skinfolds)
Any disturbance in hydration level in the body (e.g. dehydration) will affect the accuracy of the result
Tends to over-estimate body fat in very lean, muscular people and under-estimate % fat in obese people
It is the distribution of fat rather than the quantity with regard to health risk
People can be classified as ‘apples’ (android) or ‘pears’ (gynoid) according to their fat distribution
‘Apples’ have extra abdominal fat and carry a greater risk of CHD, Type 2 diabetes than ‘pears’ (extra fat around hips and thighs)