Technical Notes - Tanita DC-430MA III Instruction Manual

Technical Notes

Body composition measurement by the BIA method.
Introduction
This equipment provides estimated values for each measured value of body fat percentage, fat mass, fatfree
mass, muscle mass and bone mass by the DXA method, estimated value for the total body water measured
value by the dilution method and estimated value for the visceral fat rating by MRI method using the
Bioelectrical Impedance Analysis (BIA method).
For measurement, a mode must be selected based on body type.
1) Standard (for 5 to 99 years of age)
2) Athletic (for Athletic persons who exercise considerably more than non-athlete)
Making a distinction by body type in the measurement mode produces more reliable body composition
measurements for athletic persons, whose body compositions differ from those of average persons.
- Principles of body composition measurement
BIA is a means of measuring body composition – fat mass, predicted muscle mass, etc. – by measuring
bioelectrical impedance in the body. Fat within the body allows almost no electricity to pass through, while
electricity passes rather easily through water, much of which is found in muscles. The degree of diffi culty
with which electricity passes through a substance is known as the electrical resistance, and the percentage of
fat and other body constituents can be inferred from measurements of this resistance.
The Tanita Body Composition Analyzer measures body composition using a constant current source with
a high frequency current (6.25kHz, 50kHz, 90μA). The 4 electrodes are positioned so that electric current
is supplied from the electrodes on the tips of the toes of both feet, and voltage is measured on the heel of
both feet.
- What is the DXA method?
DXA was originally designed to measure bone mineral content, but in
the full-body scan mode the body fat percentage, fat mass, and fat free
mass of individual body parts (arms, legs, trunk) can also be measured.
The image below shows one example of body composition measurement
results obtained by DXA.
- What is dilution method?
In the dilution method, a labeled substance for a known amount is given and the concentration in
equilibrium diffusing evenly is measured to obtain the total amount of the solvent that dilutes the labeled
substance.
To measure the total body water (TBW), deuterium oxide (D2O) is generally used as the labeled substance.
Deuterium oxide uses the overall total body water as dilution space so the total body water can be obtained.
To obtain the extracellular fl uid amount, sodium bromide (NaBr) is used as a labeled substance.
Bromine (Br) is said to not enter the inside of cells, and uses extracellular fl uid as the dilution space.
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Body composition measurement results
obtained by DXA