accurate calculation of percent body fat is the true definition of
fitness and obesity
accurate measurement of Lean Body Mass is now the most rational
basis for nutritional and exercise prescriptions. The importance
of clinical body composition is now being recognized.
There is evidence that research and interest in body
composition was explored centuries ago by Archimedes, though most
of the research data that is available on human body composition
has been completed in the last forty years.
With the recent interest in personal health, nutritional
status and fitness, several methods of estimating body fat have
been developed and used in clinical settings. Various body composition
analysis techniques are reviewed in this article including:
Weighing is currently considered the "Gold Standard" of body composition
analysis. Hydrostatic measurements are based on the assumption that
density and specific gravity of lean tissue is greater than that
of fat tissue. Thus, lean tissue will sink in water and fat tissue
will float. By comparing a test subject's mass measured under water
and out of the water, body composition may be calculated. The "Gold
Standard" of body composition is a mathematical prediction.
There are several limitations to the hydrostatic weighing
technique. The equipment required to perform hydrostatic measurements
is bulky and maintenance intense. A large tank of water, usually
1000 gallons, must be maintained at a constant temperature. Equipment
to measure residual lung volume must be utilized. A calibrated autopsy
scale or its electronic equivalent, connected to an "under-water
chair" is also required. Test subjects are asked to exhale as much
air as possible from their lungs and be immersed for 10 to 15 seconds
for an underwater weight measurement to be taken. This procedure
is repeated 7 to 10 times. Total test procedures may require 45
minutes to one hour. (Cohn, 1981)
The accepted test re-test of hydrostatic weighing is
± 2.5% for comparison of consecutive tests with the same subject
and the same technician. In non-controlled settings the test re-test
variable may be significantly higher. Most of the variance is accounted
for from a lack of subject cooperation and a lack of technician
discipline and/or experience. Many tanks have not critically examined
their test/re-test results. (Lohman, et al, 1981)
(Katch, et al, 1984)
Hydrostatic weighing methodology assumes that the density
of bone in humans is constant. Thus, differences in bone density
will create test errors. African-Americans and trained athletes
are now known to have a higher bone density than non-athlete Caucasians.
The elderly and Asians have considerably lower bone density. Specialized
equations have been developed for use with African-American populations.
(Harsha, et al, 1978)
Fear of immersion, fear of infection, obesity and infirmity
are additional barriers to the Hydrostatic measurement of accurate
body composition analysis.
1953 the Metropolitan Life Insurance Company developed the first
height/weight tables to calculate the degree of individuals over
or under weight status. The data was based on "averages" from its
client base for both men and women. In 1983 the tables were revised
based on updated data.
size is an important, subjective factor utilized in the development
of the tables with small, medium and large frame determinations
changing the "ideal weight" recommendation. Improvement on frame
size determinations were implemented in 1986 with the elbow breadth
or wrist circumference measurements used to classify frame size.
The use of the Metropolitan height/weight table gives
no indication as to the degree of either obesity or leanness on
an individual basis. In the individual clinical setting, height/weight
tables can provide grossly inaccurate conclusions about an individual's
The validity of estimation of percent body fat and density
by height and weight measurements when compared to the Hydrostatic
tank is very poor with correlation coefficients in the range of
.31 to .43. (Girandola et al 1989)
Body Mass Index (BMI)
Mass Index has recently been used to quantify an individual's obesity
level. BMI is derived from a ratio equation of height squared divided
by weight. Here again, only an individual's height and weight are
used and no indication of actual lean or fat mass can be determined.
Thus, BMI offers little advantage over the existing Metropolitan
test methodology for body fat estimation with skin fold measurements
requires the use of a "caliper device" to measure the thickness
of substantial fat stores. The assumption is that substantial fat
is proportional to over all body fat and thus by measuring several
sites total body fat may be calculated.
There are many site measurements where skin fold measurements
can be taken. Currently over 100 different equations are available
to estimate body fat with the use of skin fold calipers. The wide
variety of equations reflects the problem with the accuracy of this
There are many limitations with the Skin Fold measurement
technique. The validity of skin fold measurements is at best ±6%
compared to the hydrostatic tank. Because of the inaccuracy associated
with skin fold calipers, many credible organizations such as the
U.S. Army and the Los Angeles Police Department have abandoned the
use of them. (Stevens 1983)
The estimation results obtained from skin fold measurements
vary widely from technician to technician. The "art" of skin fold
measurements requires the technician to properly identify a site
measurement and pinch the skin gathering only the fat store and
no other tissue. The error of estimate between technicians has been
reported to be ±8%. (Smith, 1977)
The assumption that 50% of human body fat is located
in subcutaneal tissues and the remaining 50% is found in intra-muscular
and essential fat (around organs) is not universally valid. Body
fat distribution and health risk varies depending on genetics, exercise
and nutritional patterns. (Cooper, et al, 1978)
Thickness and Density
The obese population represents unique limitations for
skin fold measurements. Skin fold calipers cannot open wide enough
to measure the total fat thickness, thus tends to grossly under
estimate body fat percentage in the obese population. Also of concern,
especially in the obese population, is the compression of fat by
the caliper due to variances in fat density. Again, this tends to
inaccurately estimate percent fat in the obese, the population where
accuracy is most important.
use of Anthropometric Measurement (girth and length) is a quick,
easy and inexpensive method to estimate body composition. Using
a standard calibrated cloth tape, girth and length measurements
are taken from specific points on the body.
The methodology is based on the assumption that body
fat is distributed at various sites on the body such as the waist,
neck and thigh. Muscle tissue on the other hand is usually located
at anatomical locations such as the biceps, forearm and calf. The
subjects weight, height, girth size and ratios of various site comparisons
are utilized in the calculations of percent body fat.
Although the use of anthropometric measurements provides
a reasonably reproducible value and gives a topographical assessment
of an individual, the established accuracy for the prediction of
body fat is at least ±5% compared to the hydrostatic tank.
use of Infrared (IR) light to measure fat is not a new technique.
The U.S.D.A first developed the technique to measure the fat contained
in 1 cubic centimeter sections of beef and pork carcasses after
In the human device, a "wand" from the device emits
an IR light source at about 900 nanometers into the biceps area.
The methodology is based on the ability of fat tissues to "absorb"
more IR light than lean tissue which can then be measured as a change
in the infrared level.
The only commercially available unit to predict human
body composition is manufactured by Futrex. Since the Futrex device
was first marketed for clinical use, many research articles have
been published stating that the device is not accurate and is not
recommended for clinical use in the assessment of body composition.
The original application of this IR technology was developed
on "skinned" carcasses. No research is available about IR penetration
through the skin.
The actual contribution of the IR wand measurement and
input into the height and weight calculations used in the device's
program have also been questioned. This device has not been approved
by the FDA for use. (Israel et al 1989) (Davis et
use of bioelectrical impedance was first documented in 1880 (Kalvin),
as a potentially safe, convenient and accurate technique to measure
conductivity in the body.
The method is based on the fact that the lean tissue
of the body is much more conductive due to its higher water content
than fat tissue.
A bioimpedance meter is attached to the body, at the
extremities, and a small 500-800 micro-amp, 50 kilohertz, signal
measures the body's ability to conduct the current.
The more lean tissue present in the body the greater the
conductive potential, measured in ohms. (Thomasett,
In the early 1980's, the first commercial bioimpedance
units were available to measure human body composition (RJL, Valhalla,
Space Labs etc.). These bioimpedance units utilize "linear regression"
formulas to predict body fat based on biological data input into
a single equation.
A review of the literature indicates that bioimpedance
units which utilize these linear regression equations tend to be
somewhat valid for a "normal" population, but under-predict body
fat for obese subjects and over-predict body fat of lean subjects.
The standard errors of estimate for these equations are ±5% to ±6.4%
in normal populations when compared to the hydrostatic tank.
(Jackson et al 1988) (Segal et al 1988)
1985, the first validated algorithmic equations to interpret bioimpedance
measurements were developed and patented by BIO|ANALOGICS. The use
of the algorithmic equations instead of linear regression allows
for population specific variables for lean, obese, elderly and pediatric
subjects. The National Institutes of Health (NIH) conference on
bio-impedance analysis (1994) concluded that to obtain valid predictions
of percent body fat in humans, population specific equations must
The algorithmic equations developed and patented by
BiO|ANALOGICS are population specific and validated on all types
of subjects. The current validation studies contain more than 1000
subjects with an error factor of ±3.3% and a correlation coefficient
of .88 compared to the criterion hydrostatic tank.
As mentioned earlier, the accepted test/re-test variance
with hydrostatic measurements is 2.5% when compared to itself. The
accepted test/re-test variance for bioimpedance analysis is less
than ±.5%. (Girandola 1987)
the new, state of the art technology, utilizes the algorithmic approach
of ElectroLipoGraphy (ELG) coupled with specific anthropometric
measurements to further define body fat measurements. This technique
was developed by BIO|ANALOGICS to further improve the original,
patented algorithmic formula.
A total of five (5) to six (6) site measurements are
entered into the algorithmic formula to increase the correlation
coefficient to .91, and to reduce the standard error of estimate
to ±2.8% compared to the hydrostatic tank. No other clinically available
unit provides the Scientific accuracy, reliability and efficiency
across a wide range of subjects. (Girandola et al
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