Technical Notes - Tanita SC-240 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 5-99 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 difficulty 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 (50 kHz, 90 µA). The 8 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. The current flows into the upper limbs or lower limbs, depending on the body part(s) to
be measured.
- 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.
Body composition measurement
results obtained by DXA
(Lunar Co., Ltd; DPX-L)
- 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 fluid amount, sodium bromide (NaBr) is used as a
labeled substance. Bromine (Br) is said to not enter the inside of cells, and uses extracellular fluid as
the dilution space.
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