OMRON Bioelectrical Impedance Analyzer ( the two pictures above show device we will be using in class and the proper way to hold it)
Bioelectrical impedance analysis (BIA) is a widely used method for
estimating body composition. The technology is relatively simple, quick,
and noninvasive. BIA is currently used in diverse settings, including private
clinicians offices, health clubs, and hospitals, and across a spectrum of
ages, body weights, and disease states. Despite a general public perception
that BIA measures of body fat, and the technology actually determines the
electrical impedance of body tissues, which provides an estimate of total
body water (TBW). Using values of TBW derived from BIA, one can then
estimate fat-free mass (FFM) and body fat (adiposity). In addition to its
use in estimating adiposity, BIA is beginning to be used in the estimation
of body cell mass and TBW in a variety of clinical conditions.
BIA measures the opposition of body tissues to the flow of a small
alternating current.
Impedance is a function of two
components (vectors): the resistance of the tissues themselves, and the
additional opposition (reactance) due to the capacitance of membranes,
tissue interfaces, and nonionic tissues. The measured resistance is approximately
equivalent to that of muscle tissue.
Impedance measures vary with the frequency of the current used. Applications of
BIA increasingly use multifrequency measurements, or a frequency
spectrum, to evaluate differences in body composition caused by
clinical and nutritional status. By using the impedance measurements along with a person's height and weight, and body type (gender, age, fitness level), it is possible to calculate the percentage of body fat, fat-free mass, hydration level, and other body composition values. Conventional BIA normally uses underwater weighing as its method of reference.
Using BIA to estimate person's body fat assumes that the body is within normal hydration ranges. When a person is dehydrated, the amount of fat tissue can be overestimated. Factors that can affect hydration include not drinking enough fluids, drinking too much caffeine or alcohol, exercising or eating just before measuring, certain prescription drugs or diuretics, illness, or a woman's menstrual cycle. Measuring under consistent conditions (proper hydration and same time of day) will yield best results with this method.
Because BIA can be affected by body hydration, many professionals may use this method as a means of tracking the hydration status of their patients. This is especially important for athletes who are training or performing, as well as for the chronically ill.
Many people desire a "rating system" for assessing their current level of body fat.
The following table provides a meaningful rating system.
FEMALE
Age Excellent Good Fair Needs improvement
19-24 18.9 % 22.1 % 25.0 % 29.6 %
25-29 18.9 % 22.0 % 25.4 % 29.8 %
30-34 19.7 % 22.7 % 26.4 % 30.5 %
35-39 21.0 % 24.0 % 27.7 % 31.5 %
40-44 22.6 % 25.6 % 29.3 % 32.8 %
45-49 24.3 % 27.3 % 30.9 % 34.1 %
50-54 26.6 % 29.7 % 33.1 % 36.2 %
55-59 27.4 % 30.7 % 34.0 % 37.3 %
60 + 27.6 % 31.0 % 34.4 % 38.0 %
MALE
Age Excellent Good Fair Needs improvement
19-24 10.8 % 14.9 % 19.0 % 23.3 %
25-29 12.8 % 16.5 % 20.3 % 24.4 %
30-34 14.5 % 18.0 % 21.5 % 25.2 %
35-39 16.1 % 19.4 % 22.6 % 26.1 %
40-44 17.5 % 20.5 % 23.6 % 26.9 %
45-49 18.6 % 21.5 % 24.5 % 27.6 %
50-54 19.8 % 22.7 % 25.6 % 28.7 %
55-59 20.2 % 23.2 % 26.2 % 29.3 %
60 + 20.3 % 23.5 % 26.7 % 29.8 %
