This document discusses the use of bioelectrical impedance analysis (BIA) to evaluate body composition in athletes. It finds that BIA may provide acceptable estimates of body composition in groups of athletes when testing conditions are well controlled, but has limitations for detecting small changes in individuals. Key factors that need to be controlled include hydration levels, recent exercise, diet, and skin temperature as these can influence impedance measurements. There is also a tendency for BIA to overestimate body fat levels in lean athletes and especially in African American athletes. More research is still needed on the use of BIA in female athletes as well.

1. Use of bioelectrical impedance analysis measurements as
an evaluation for participating in sports1’2
Karen R Segal
ABSTRACT Bioelectnical impedance analysis (BIA) has p0-
tential in the area of sports and exercise as a method for evaluating
body composition in groups of athletes. BIA probably holds less
promise for detecting small changes in percentage fat within an
individual. Available data in athletes have indicated an urgent need
to control for testing conditions such as hydration, temperature,
glycogen stores, and preceding diet and exercise. There are almost
no data available for female athletes, but acceptable results have
been reported in males when conditions are well controlled. There
is, however, a tendency for BIA to overestimate percentage body
fat, and more so in African American athletes. BIA is also poten-tially
useful for assessing the hydration status in wrestlers, but it is
advisable to use untransformed BIA measurements rather than to
convert resistance measurements to body fat because of the ques-tionable
hydration status in these athletes. Untransformed results
are potentially useful in evaluating the clinical status of athletes at
risk for abnormal hydration because of extreme dieting practices.
Am J C/in Nutr 1996;64(suppl):469S-7 IS.
KEY WORDS Bioelectrical impedance analysis, athletes,
body composition, exercise
INTRODUCTION
There has been considerable interest in the use of bioelec-tnical
impedance analysis (BIA) in the evaluation of body
composition in sports and exercise because body composition
has a significant effect on athletic performance and because
exercise has the potential to alter body composition. Body
composition is an important determinant of performance in
many sports: high fat-free mass (FFM) is needed for increased
power and strength, whereas leanness (low percentage body
fat) is important for sports in which body weight is unsup-ported,
in which class of competition is determined by body
weight (wrestling), or in which aesthetic considerations man-date
a certain body habitus (gymnastics, figure skating, and
dance).
Accordingly, there is a need for a body-composition assess-ment
technique that is safe, noninvasive, rapid, and at the same
time reliable, accurate, and sensitive to the small differences in
body composition that may occur oven the course of physical
training. BIA apparently meets many of these needs: measure-ments
are made rapidly and noninvasively, the information
provided by BIA is more specific than body weight alone, the
method is relatively inexpensive compared with other body-composition
methods and is suitable for field studies or large-scale
epidemiologic investigations of groups, and it is appno-priate
for comparative characterization of the body
composition of athletes in different sports.
As an evaluation tool for athletes participating in sports,
bioelectrical impedance has an advantage over body weight
alone provided that it is reasonably accurate and reliable.
Accuracy and reliability are highly dependent on the test con-ditions
and the equations used to convert the raw impedance
data into some measure of body composition. The usefulness of
BIA in athletes depends on whether the desired use is for
groups of athletes on for individuals. There is probably greater
value in the use of BIA for groups and for comparisons of
groups than for detecting changes within individual athletes
because the magnitude of these changes is likely to be rela-tively
small.
PROBLEMS WITH USE OF BIA
There are several problems with the use of BIA in athletes
and several issues that require further research attention. In
general, there are two problems related to the use of BIA in
sports and exercise: altered physiologic factors and a limitation
in prediction equations that therefore raises statistical concerns.
Some of the physiologic considerations in the use of bioelec-trical
impedance in athletes are the need to control for condi-tions
such as amount of hydration, skin temperature, the last
bout of exercise, glycogen stones (1 ), and chemical maturity in
younger athletes (2).
Acute exercise alters factors such as temperature, hydration,
and glycogen stones, which are physiologic factors that can
affect the body-composition estimation from BIA. Athletes and
others who exercise regularly are frequently in the postexencise
state and, therefore, the physiologic conditions of testing are
likely to be more varied in these individuals than in sedentary
individuals. Additionally, within individuals, it is possible that
there is more variability in hydration because of acute bouts of
exercise, which would compound the error in repeated mea-surements
within the same individual. Decreases in body water
from sweating or loss of the water bound to body glycogen
stores are manifest as an increased BIA-measured body nesis-
I From the Division of Pediatric Cardiology, Department of Pediatrics,
Cornell University Medical College, New York.
2 Address reprint requests to KR Segal, Division of Pediatric Cardiol-ogy,
Department of Pediatrics, Cornell University Medical College. Room
N-134, 1300 York Avenue, New York, NY 10021.
Am J C/in Nuir l996;57(suppl):469S-7lS. Printed in USA. 0 1996 American Society for Clinical Nutrition 4695
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2. 4705 SEGAL
tivity. When converted to body-composition indexes by use of
prediction equations, this increased resistance or impedance
appears to underestimate FFM and overestimate percentage
body fat.
Regarding the limitations of prediction equations for con-verting
measured resistance values to some meaningful index
of body composition in athletes, there are a few statistical
considerations. The first is that it is likely that equations will be
biased when applied to a group (athletes) who are at one end of
the spectrum of adiposity. The second is that the development
of specific prediction equations for athletes in various sports is
hampered by a narrow range in fatness. In addition, there may
be physiologic factors intrinsic to the athletes, such as an
increased ratio of muscle to total FFM on altered bone density
that further complicate both the accuracy of existing equations
for predicting body composition from BIA on the development
of new equations (3). Variation in the composition of the
fat-free body would mandate use of a multicompartment vali-dation
model because the assumptions pertaining to the chem-ical
composition of the FFM would be violated both in the BIA
model and in the criterion method.
There may be an intrinsic bias in the use of impedance in
athletes because of a generally lower body fat percentage in
athletes than in the normal population such that fatness tends to
be overestimated at the lower end of body fat values (ie,
regression to the mean) (4). This is an apparent regression
artifact related to the fact that at the extreme of leanness,
predictive equations tend to overestimate fatness whereas at the
extreme of obesity predictive equations tend to underestimate
fatness. Several investigators have developed equations just to
estimate body composition from BIA in the obese end of the
spectrum, and so too, specific equations have been developed
for use at the lean extreme. But there is a tradeoff because it is
harden to show a strong relation when the range in body
composition is extremely limited and restricted, as it would be
within homogeneous groups of athletes.
STUDIES IN ATHLETES
Of the comparative studies of body-composition techniques
in athletes, a reasonable degree of accuracy and reliability in
the impedance method has been reported only when test con-ditions
are well controlled. This is particularly an issue in
athletes because they tend to frequently keep themselves in an
“uncontrolled state” because of postexencise conditions. Skin
temperature, strenuous exercise, dehydration, and glycogen
depletion significantly affect the measured impedance values
( 1 , 5). Preceding diet and exercise are also important factors in
the use of impedance in athletes before competition: carbohy-drate
loading tends to inflate estimated FFM by impedance
because of the extra water bound to glycogen. Aside from the
effect of recent exercise on sensible and insensible water loss,
exercise pen se can affect measured body resistivity by means
of increased skin temperature, increased vascular perfusion,
hypenemia, increased cutaneous blood flow, and vasodilation
(6). Accordingly, it is advisable to wait several hours after
strenuous exercise before impedance measurements are made.
Lukaski et al (7) conducted the largest comparative study of
BIA with densitometry in athletes in a group of 104 male and
female college athletes who played basketball, football, swim-ming,
wrestling, track, and volleyball. These athletes under-went
measurements of BIA and body density both in an un-controlled
state with no restrictions on exercise, hydration, and
time of last feeding, and 2 h after a light meal with no
preceding exercise. Not controlling for hydration, last exercise,
on food intake resulted in underestimated percentage fat by BIA
compared with percentage fat measured by underwater weigh-ing
because in the uncontrolled state resistance was greater;
therefore, conductance (height squared/resistance) was in-creased.
When FFM was predicted, although there were no
significant differences between the BIA and measured values,
the correlation was stronger when test conditions were con-trolled.
When the test conditions were controlled, the predictive
error for BIA in male and female athletes was 2.8% fat. This
error was reduced by 30% by controlling the test conditions.
There are several limitations to much of the work that has
been done pertaining to the use of BIA in evaluating athletes.
Many of the studies describe only small samples. Perhaps the
most important limitation of some of the available data from
athletes is that it is clear from the studies by Lukaski that the
testing conditions must be well controlled, but few studies
applied such rigorous control over the athletes’ physiologic
state. Lastly, in the only published work pertaining to female
athletes, by Webster and Barr (8), BIA was assessed in corn-petitive
gymnasts and skaters only in comparison with skinfold
thicknesses. Therefore, further validation of the method spe-cifically
in female athletes is needed.
The largest body of information regarding BIA in athletes is
in the sports of football and wrestling. Several studies of
collegiate football players have indicated that impedance may
not be more accurate than anthropometry when the appropri-ately
specific prediction equation is applied to skinfold-thick-ness
measurements (9, 10). Hortobagyi et al (10) reported that
BIA overestimated fat by ı5% in blacks and 3% in whites, and
that the addition of BIA measurements did not improve the
prediction of body composition above that by body mass index
alone. Furthermore, compared with hydrodensitometry, BIA
was apparently less accurate than skinfold thickness measure-ments.
Clark et al (9) noted that BIA overestimated fatness by
ı4%, especially in blacks, and that estimates of body compo-sition
were not better than those from skinfold thicknesses with
use of the equation developed by Jackson and Pollack (11). In
addition, there may be racial differences and physiologic van-ation
in bone mineral due to physical activity per se that affect
the relation between impedance and the criterion body-compo-sition
method used to develop prediction equations for estimat-ing
body composition from measured impedance (3, 10). For
example, it has been noted that bioelectnical impedance over-estimates
percentage fat in black football players (10). Al-though
race-specific equations for calculating percentage fat
from body density (measured by hydrodensitometry) have been
developed to take into account the greater bone density in
blacks (12), most bioelectnical impedance equations do not
adjust for racial differences.
There are currently no equations to estimate body composi-tion
by impedance that are sufficiently precise in these athletes
and it is unlikely that there ever will be, given the intrinsic
minimum error in the method and the small changes that are
considered meaningful by athletes and their coaches. Data
pertaining to changes in body composition, as may be derived
from testing athletes before and after training regimens, need to
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3. BIOELECTRICAL IMPEDANCE IN SPORTS 471S
be considered in light of the minimum detectable change given
the error of the method, which at best is reported to be 2.8% fat.
This is actually a large change for an already fairly lean athlete
trying to get even leaner to optimize performance. An error of
3% body fat in an athlete with only 5% body fat is an error of
60%.
Under conditions in which the use of bioelectrical impedance
is not appropriate for determining the body fat content in
athletes, the body water information derived from impedance
may nevertheless provide relevant clinical information. Large
changes in measured resistance and reactance in wrestlers who
are measured repeatedly may indicate athletes at risk for se-quelae
of disturbed hydration.
BIA IN ADULT FITNESS SETTINGS
The BIA method has potential application in health clubs and
other adult fitness settings for body-composition assessment.
For BIA of normal adults exercising in health clubs, care
should be taken in the training of the test operator to ensure that
the electrodes are applied properly, that the appropriate predic-tion
equations are used, and that measurements are obtained
under controlled test conditions (ie, normal hydration, diet, and
resting state). For monitoring changes in body composition that
occur as the result of weight control on exercise training negi-mens,
the BIA method may not be more accurate than simple
use of anthropometry. Because exercise without diet leads to
only slow and small changes in body weight, the sensitivity of
the impedance method may not be sufficient for detecting small
changes in body composition in individuals, but may be ade-quate
for tracking trends in groups and populations.
CONCLUSIONS
In summary, there is potential usefulness for BIA measure-ment
in sports and exercise. Given the appropriate care and
control of the athletes’ physiologic state and testing conditions,
the method may provide an acceptable estimate of body corn-position;
however, the sensitivity of the method for detecting
small changes in body composition as the result of further
training is doubtful. Furthermore, there is an apparent racial
bias that might be as much due to error in the criterion method
and prediction equations as to limitations in the BIA method.
There is also a lack of adequate published information on the
use of BIA in female athletes. U
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