Tanita DC-430MA III Instruction Manual page 34

Technical Notes (continued)
- Factors giving errors in measurement
In the BIA method, impedance is measured and the body composition is calculated based on the value. It is
known that impedance changes by the amount of the total body water that occupies about 60% of weight
and the change in its distribution and temperature change. Therefore, for the purpose of research or for daily
repeating of measurements, the measurement conditions must be kept constant. Measurement under the
changing conditions of temperature and total body water distribution or blood fl ow volume of extremities
due to exercising, taking a bath, etc., affects the measurement result since the electric resistance in the body
also changes.
Therefore, it is recommended to measure under the following conditions for stable measurement.
1) 3 hours have passed after getting up and normal lifestyle activities are carried out during this period.
(The impedance transits staying at a high level if you remain sitting after getting up or drive a car, etc.)
2) 3 hours or more have passed after eating. (For 2 to 3 hours after eating, the impedance has a tendency to
decrease.)
3) 12 hours or more have passed after vigorous exercise for measurement. (The tendency toward changes in
impedance is not stable depending on the type and rigorousness of the exercise.)
4) If possible urinate before taking measurement.
5) For repeated measurements, measure at the same hour as much as possible. (At the same time of
measurement of weight, the measurements can be made more stable by measuring at the same time of the
day)
Very stable measured values can be obtained by measuring under the above conditions.
And in the development of this equipment, the following 6 items were set as conditions for the regression
equation.
1) Prohibition of alcohol intake for 12 hours before measurement
2) Prohibition of excessive exercise for 12 hours before measurement.
3) Prohibition of excessive eating and drinking the day before measurement
4) Prohibition of eating and drinking for 3 hours before measurement
5) Urination just before measurement
6) Avoid measurements during menstruation (for female)
2) Inter-day changes
The diagrams below offer examples of actual measurements made
of inter-day changes. A study was done to determine the degree of
change in the impedance between the feet during dehydration; the
fi rst two days represent a normal daily routine, while in the latter
two days a state of dehydration was induced using a sauna.
No signifi cant inter-day change was measured in body weight,
impedance between the feet, or body fat percentage during the
normal daily routine. During the dehydrated state, however, a drop
in body weight of 1kg was noted, with the impedance between the
feet rising approximately 15Ω on the fi rst day of dehydration and
30-35Ω on the second day. As a result, body fat percentage was up
by around 1% on the fi rst day of dehydration and by 1.5-2% on the
second day.
As mentioned earlier, impedance increases when body weight
is reduced (such as by dehydration), and decreases when body
weight is increased through excess consumption of food and drink.
The inter-day change in impedance is thus inversely proportional
to the change in body weight.
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