study was conducted to evaluate the validity of bioelectrical impedance
as an accurate assessment of body composition. Four hundred and
eighteen male and female volunteers were used as subjects. Each
subject reported to the Exercise Physiology Lab at the University
of Southern California in a normally hydrated condition. Body composition
evaluation was made by hydrostatic weighing (H2O)
and bioelectrical impedance (Imp).
was performed in a seated position in a 1000-gallon tank. A minimum
of 5 trials was performed on each subject. Residual lung volume
was measured, immediately prior to hydrostatic weighing, utilizing
the oxygen dilution method and employing a Hewlett-Packard nitrogen
analyzer. Body fat was calculated using the formula of Brozek et
al. (4.57/Dd-4.142x100%). Bioelectrical impedance was measured (BIO|ANALOGICS'
ELG System) on each subject (prior to H20
weighing) employing recently developed algorithmic equations. The
method involves the use of a tetrapolar lead system where an 800uA
constant current source at 50khz was applied to the subject and
a measurement of impedance (resistance and reactance) was obtained.
body fat for the males (N=208) was 15.2% measured by H20 and 14.4%
as measured by Imp. The range of body fat for this group was 3-35%.
The validity coefficient for this group was r=0.76 and the standard
error of estimate (SEE) was 3.24%. The corresponding value was for
the female group (N=211) were as follows: Average body fat by H20=23.9%;
by Imp=23.4%; range=11-39%; validity coefficient, r=-0.83; SEE=3.15%.
Validity for the combined sample was r=-0.88; SEE=3.30%. The results
of the present study support the use of this bioelectrical impedance
technique as simple, reliable and yet accurate method of assessing
the percent of body fat in males and female in the clinical setting.
and Conclusions] [Conclusions]
relationship between human obesity and long-term health problems
has been well-established 2, 25, 27. Obesity
and dietary excess have been strongly associated with diseases such
as coronary heart disease, stroke, hypertension, diabetes, cancers
of the digestive and reproductive systems, and osteoporosis
31. For several decades the use of height/weight tables and
Body Mass Index (BMI) has been employed for health assessment and
definition of overweight. However, the overweight person is not
necessarily the obese person 12. Obesity
is precisely defined as an excess of body fat frequently resulting
in a significant impairment of health 30.
Twenty-five percent of the United States population is reported
to be obese. It is clear that the assessment of body composition
(body fat and fat-free weight) in humans has become increasingly
important not only for research but for clinical applications as
for assessing body composition have been available since the 1950's.
Most of these methods involve fairly sophisticated instrumentation
and/or techniques, and are considered research laboratory procedures.
The NIH has stated that the precise determination of the amount
of body fat requires technically sophisticated methods that are
available only in research laboratories 30.
Excellent reviews of these procedures are available in reviews by
Buskirk 5 and Lukaski 21.
Recently another method for the prediction of body composition has
been developed. This technique has been termed bioelectrical impedance.
Basically this method makes use of the fact that electrical conductivity
of the human body occurs primarily through the water and electrolytes
of the fluid spaces (Total Body Water, TBW) 5, 21.
The relationship between impedance and body composition was first
shown by Thomasset 26. The technique has
been shown to be simple to administer, involving minimal technician
training. However, controversy has arisen regarding the accuracy
of the bioimpedance technique. Investigators have found the technique
to be reliable 19, 20, 21, with reasonable
(R=0.70-0.80) 7, 11, 13, 24, 28 to excellent
validation against densitometry (R=0.88-0.93) 20.
On the other hand, more recent investigators 14,
24 have criticized the prediction accuracy of the technique,
reporting SEE's of between 4.6-6.4% fat, concluding that the equations
(RJL Systems) provided for the technique gave unsatisfactory results.
light of the increasing clinical significance of human body composition
and the controversy regarding the impedance methodology, the purpose
of the present study was to evaluate the validity of a specific
bioelectrical impedance analyzer, which incorporates a recently
developed algorithmic method to predict human body composition.
and Conclusions] [Conclusions]
total of 602 subjects (317 females and 285 males) volunteered for
body composition evaluation. Subject characteristics appear in Table
1. Subjects reported to the laboratory in a fasted (4-5 hours) and
normally hydrated condition. A series of circumference measurements
were taken using a cloth metric tape. A complete description of
the sites and method appear in a text by Behnke and Wilmore 1.
Bioelectrical impedance (BIO|ANALOGICS) was measured in the supine
position, with sensor electrodes placed at standard locations on
the right wrist and right ankle. An excitation current of 800 uA
at 50 kHz was introduced into the subject and the voltage drop was
measured. Residual lung volume was measured utilizing the oxygen
dilution method described by Wilmore 29.
Height was measured by a standard stadiometer and weight was measured
to the nearest 50 grn. using a Horns balance beam scale. Hydrostatic
weighing was done in a 1000-gallon tank with subjects in a seated
position and suspended from a calibrated Chatillon autopsy scale.
Underwater trials were continued until weight stabilized (avg. 4-8
trials). Density was calculated according to the method of Goldman
and Buskirk 10 and % fat calculated according
to the formula of Brozek, et al 4. These
methods have been well standardized in our laboratory 8,
and Conclusions] [Conclusions]
results of the body composition evaluation for the 602 subjects
appear in Table 1. The mean values for the males and females are
typical for the age profile of the subjects. As can be seen, the
average values for densitometry and bioelectrical impedance are
very similar, with only 0.5 % fat separating the mean values for
the males. Table 3 illustrates the correlation coefficient between
% fat, calculated by densitometry (criterion method), and % fat
predicted by impedance. The values obtained in the present study
were similar in magnitude to the values reported by several investigators
7, 11, 13, 24. We and other investigators
7, 11, 13, 14, 24 have not been able to replicate
the extremely high validity coefficients reported by Lukaski, et
the present study, the SEE's for the females and males, respectively,
were 3.42% and 3.77% fat (R=0.80, 0.71). These values are similar
to those reported by Guo, et al 11, but considerably
lower than those reported by other investigators 13,
14, 24. The discrepancies of various bioimpedance techniques
validated against densitometry found between investigators may have
been caused by use of different formulas in the specific impedance
analyzers. Colvin, et al 7 utilized three
different analyzers on the same subjects and reported R-values ranging
from 0.72-0.81 and SEE's from 2.4-4.9%.
et all 14 have criticized the impedance method
due to the low validity coefficients and high SEE's they found (R=0.71-.76
and SEE=4.6-6.4% fat) (RJL Systems). Furthermore, they reported
that BMI is at least as good a predictor of % fat as the impedance
device they tested with correlation of R=0.74-0.75 and SEE's of
4.3-4.8%. In the present study the R-values for BMI were 0.69, SEE's
were 4.1 and 4.6%. Our data would indicate that the bioelectrical
impedance system tested is certainly a better predictor of body
composition than BMI.
use of anthropometric methods, such as skinfolds and circumferences
have long been advocated as convenient, inexpensive, and simple
procedures to predict body composition 1, 15.
Unfortunately, many of the prediction formulas generated by these
methods (especially skinfolds) tend to be population specific. Jackson,
et al 14 have reported validity coefficients
of R=0.92 (males) and R=0.88 (females) between the sum of 7 skinfolds
and % fat measured by densitometry. The SEE's were 2.6-3.6% fat.
However, some investigators 6, 18 have indicated that the prediction
accuracy of the skinfold method is approximately ±5% body fat. Pollock
and Jackson 23 cautioned that the validity
of estimating body density in the obese may be suspect when using
skinfold fat measures. Similarly, Bray, et al 3
found that skinfold measurements had high variability, and considerable
interobserver variability, and concluded that the use of skinfold
calipers is not to be recommended in assessing or following obese
investigators 13 have evaluated the combination
of bioelectrical impedance and anthropometric variables in predicting
body composition. Guo, et al, used a combination of skinfolds and
circumferences together with impedance. The best of skinfolds and
circumference measurements for the female group yielded a validity
coefficient of R=0.85 with a SEE of 3.83% fat, when compared with
densitometry. The addition of impedance to the regression formula
increased the R to 0.90 and decreased the SEE to 3.22%. For the
male group a similar analysis resulted in a smaller SEE (from 3.32%
to 3.28%), but no change in the R-value. Hodgdon and Fitzgerald
13 added a combination of skinfolds; and
circumferences to impedance in an attempt to improve the prediction
accuracy. With the anthropometric values the R-values increased
from 0.79 and 0.82 to 0.87 and 0.87, for the male and female groups
respectively. Similarly, the SEE's were reduced from 5.01 and 4.25%
to 3.90 and 3.61%, for males and females.
the present study circumference measures were obtained on 419 (211
females and 208 males) of the original 602 subjects. Utilizing prediction
equations (BioAnalogics) which incorporated a series of circumference
measures (including circumference ratios) in combination with bioelectrical
impedance, percent body fat was determined. For the female group
the multiple correlation was R=0.89 (R2=79%) and the SEE=2.68%.
The values (R=0.83; R2=68%; SEE=3.03%) for the males, though not
as good as the female group, still demonstrated a substantial improvement
in predictive ability with the addition of the circumference equations.
Our data is in agreement with that of Hodgdon and Fitzgerald 13
who have shown an improvement in both correlation and SEE with a
combination of anthropometric and impedance measurements. The SEE's
found in the present study are less than those reported by Hodgdon
and Fitzgerald and the present technique did not require the use
and Conclusions] [Conclusions]
evaluation of body composition is an important component of a preventive
health examination, especially considering the incidence of obesity
in the United States. Most of the accurate methods for measuring
body fat are limited to the research laboratory or are extremely
expensive. The bioelectrical impedance system tested has been shown
to be a simple, reliable and yet accurate method of assessing the
percent of body fat in males and females in the clinical setting.
The present study also indicates that the inclusion of circumference
measurement equations added substantially to the accuracy of the
impedance method and makes it an ideal technique that can be implemented
in research laboratories as well as the non-research clinical setting.
and Conclusions] [Conclusions]
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and Conclusions] [Conclusions]