2.6
4.2
Article
Practical but Inaccurate? A-Mode
Ultrasound and Bioelectrical
Impedance Underestimate Body
Fat Percentage Compared to DualEnergy X-ray Absorptiometry in
Male College Students
Markus Olinto, Victor César Lins, Gabriel Rocha, Marco Aurélio Dourado and Maurilio Dutra
https://doi.org/10.3390/jfmk9030113
Journal of
Functional Morphology
and Kinesiology
Article
Practical but Inaccurate? A-Mode Ultrasound and Bioelectrical
Impedance Underestimate Body Fat Percentage Compared to
Dual-Energy X-ray Absorptiometry in Male College Students
Markus Olinto 1,2 , Victor César Lins 2 , Gabriel Rocha 1,2 , Marco Aurélio Dourado 2
1
2
*
Citation: Olinto, M.; Lins, V.C.; Rocha,
G.; Dourado, M.A.; Dutra, M.
Practical but Inaccurate? A-Mode
Ultrasound and Bioelectrical
Impedance Underestimate Body Fat
Percentage Compared to Dual-Energy
X-ray Absorptiometry in Male College
Students. J. Funct. Morphol. Kinesiol.
2024, 9, 113. https://doi.org/
and Maurilio Dutra 1,2, *
Faculty of Physical Education, University of Brasília, Brasilia 70910-900, Brazil;
markusolinto@gmail.com (M.O.); gabricolico@gmail.com (G.R.)
Exercise and Health Research Group, Campus Estrutural, Federal Institute of Education, Science and
Technology of Brasilia, Brasilia 71200-020, Brazil; victorcesardiaslins@gmail.com (V.C.L.);
douradopersonal@gmail.com (M.A.D.)
Correspondence: maurilio.dutra@ifb.edu.br; Tel.: +55-61-21032160
Abstract: Bioelectrical impedance (BIA) and ultrasound (US) have become popular for estimating
body fat percentage (BF%) due to their low cost and clinical convenience. However, the agreement of
these devices with the gold-standard method still requires investigation. The aim was to analyze the
agreement between a gold-standard %BF assessment method with BIA and US devices. Twenty-three
men (aged 30.1 ± 7.7 years, weighing 82.5 ± 14.9 kg, 1.77 ± 0.05 m tall) underwent dual-energy X-ray
absorptiometry (DXA), BIA (tetrapolar) and US (three-site method) %BF assessments. Pearson and
concordance correlations were analyzed. A T-test was used to compare the means of the methods,
and Bland–Altman plots analyzed agreement and proportional bias. Alpha was set at <0.05. The
Pearson coefficients of BIA and US with DXA were high (BIA = 0.94; US = 0.89; both p < 0.001). The
concordance coefficient was high for BIA (0.80) and moderate for US (0.49). The BF% measured by
BIA (24.5 ± 7.5) and US (19.4 ± 7.0) was on average 4.4% and 9.6% lower than DXA (29.0 + 8.5%),
respectively (p < 0.001). Lower and upper agreement limits between DXA and BIA were −1.45 and
10.31, while between DXA and US, they were 2.01 and 17.14, respectively. There was a tendency of
both BIA (p = 0.09) and US (p = 0.057) to present proportional bias and underestimate BF%. Despite
the correlation, the mean differences between the methods were significant, and the agreement limits
were very wide. This indicates that BIA and US, as measured in this study, have limited potential to
accurately measure %BF compared to DXA, especially in individuals with higher body fat.
Keywords: body fat; bioelectrical impedance; ultrasound; dual-energy X-ray absorptiometry
10.3390/jfmk9030113
Academic Editor: Roland Van den
Tillaar
1. Introduction
Received: 3 June 2024
Body composition assessment and research date back to the 1940s and 1950s [1,2].
They became more relevant and advanced together with the increase in obesity and related
chronic diseases in the mid-1970s, as well as with the identification of sarcopenia as a
relevant health concern in the late 1980s [3]. Since then, a wide range of techniques have
been developed trying to accurately assess body composition (i.e., body fat and muscle
mass) in children/teenagers, adults and the elderly. Of note, valid and accurate body
composition assessment is essential for diagnostic and clinical purposes in health and
disease [4].
There are some powerful and accurate reference methods to distinguish body mass
components, such as underwater weighing, air replacement plethysmography, neutron
activation analysis, computed tomography and dual-energy X-ray densitometry (DXA) [5].
Among these, DXA is widely used as a gold-standard reference method to assess the
accuracy and agreement of other methods [6–10].
Revised: 20 June 2024
Accepted: 20 June 2024
Published: 28 June 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
J. Funct. Morphol. Kinesiol. 2024, 9, 113. https://doi.org/10.3390/jfmk9030113
https://www.mdpi.com/journal/jfmk
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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In clinical settings, such as during nutritional evaluation and ambulatory visits, as
well as in sports, fitness or wellness contexts, a wide range of indirect methods have
been used to assess body fat percentage due to the fact that they are low cost, less timeconsuming, transportable and have no side effects [5]. The most used indirect methods
include calculation by analytical formulas from simple anthropometric traits and caliper
testing. Of note, bioelectrical impedance (BIA) and ultrasound (US) scanning have gained
attention in clinical and research studies [5,8].
BIA devices are generally simple to use, inexpensive and avoid radiation exposure.
This method is based on the electrical properties of the body and determines the resistance
resulting from an electrical current passing through the body [11]. The subject’s weight,
height and age are considered to estimate total body water. Then, specific equations
are applied to determine the body fat percentage (BF%) [6]. Several BIA devices are
commercially available, and they have been applied to assess body fat in obese people,
young men and women and to analyze the risk of osteoporosis development [11].
US techniques have also become common in the last decade. These devices identify
adipose tissue using ultrasound waves that travel into body tissues. This method is noninvasive and non-traumatizing to the subject [12]. So, some studies have been trying to
assess US accuracy to measure body fat in different populations, such as male college
students [13] and athletes [14]. Thus, BIA and US have been also proposed as possible
alternatives to assess and monitor BF% in the general population.
However, both BIA and US are not free from potential bias. As they are indirect
methods, several factors may influence the result. Height, sex, age, ethnicity, total body
water, body sites of US measurement (protocol), nutritional status and physical activity are
among possible confounding variables to the measurements [5,12]. Furthermore, several
equipment models are available, which makes it difficult to establish standard protocols. In
this sense, the validation and agreement of these procedures with gold-standard methods
are still required.
The present study aimed to assess the agreement of measurement of BF% obtained by
a tetrapolar bioimpedance analyzer and an A-mode US scanner using a three-site protocol
compared to DXA in a group of male college students.
2. Materials and Methods
2.1. Participants and Study Design
This is a cross-sectional study. A convenience sample of healthy male college students
was recruited to participate. The inclusion criterion was enrollment in any undergraduate
or graduate course at the university. Data collection occurred in the Image Laboratory of the
Faculty of Physical Education. All men who volunteered to participate and gave informed
consent were included in the study. Twenty-three subjects completed all the analysis.
2.2. BF% Assessment
All subjects underwent BF% assessment in the morning, between 9 h and 11 h, in
the following order: BIA, US and DXA. Volunteers were dressed in light clothes and
were instructed to remove all jewelry and metals prior to examinations. A tetrapolar
BIA device was used in this study (OMROM HBF 514-C® , Omron Healthcare Co., Ltd.,
Kyoto, Japan) to assess body weight and BF%. The BIA sends a weak electric current
(50 kHz in the present device) through the body, and the resulting voltage is used to
calculate bioelectrical impedance, which is divided into resistance and reactance. These
measurements can be used to estimate total body water, fat-free mass and fat mass [11]. It
is important to note that the exact equation used by this specific BIA device is proprietary
and not publicly known. The height of the participants was also evaluated using a wall
stadiometer (Sanny®, São Paulo, Brazil) and body mass index (BMI) was derived from
Quetelet’s formula (weight/height2 ).
An A-mode, 2.5 MHz, portable US device (BodyMetrix BX2000® system, Intela Metrix,
Concord, CA, USA) was used. The US emits high-frequency sound waves to penetrate body
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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tissues. Differentiation of body tissue interfaces is determined based on the thickness of
tissue and the length of time it takes for the ultrasonic waves to pass through and reflect back
into the transducer [8]. Measurements were performed according to the manufacturer’s
instructions. A thin layer of US gel was applied to the probe and then placed perpendicular
to the point of skin contact at each site. The Bodyview® software (version BodyView
ProFit 3.0.9.22073-N, IntelaMetrix, Concord, CA, USA) was used to analyze images and to
measure the thickness of adipose tissue at each site. BF% was derived from calculations
using the thickness of the adipose layer of the chest, abdomen and thigh, analogous with
the skinfold method and adapted from the Jackson–Pollock three-site protocol for men [15].
All evaluations were performed by the same trained, certified technician.
DXA-derived BF% was measured using a Lunar densitometer, model DPX (General
Eletric-GE, Rommelsdorf, Germany). The equipment was calibrated daily and weekly
according to the manufacturer’s instructions. Participants were instructed to lie quietly in a
supine position with their arms at their sides on the scanning bed. Scanning of the entire
body was performed.
2.3. Statistical Analysis
The normality of the data was assessed using the Shapiro–Wilk test. All BF% measurements presented parametric distribution. Correlations between BMI-, BIA-, US- and
DXA-derived BF% were analyzed with the Pearson coefficient and the concordance correlation coefficient (simple agreement analysis). One sample T-test was used to compare the
mean differences between BF% derived from DXA and the other methods (DXA—BIA and
DXA—US). The Bland–Altman plots were used to analyze agreement between DXA and
BIA, as well as between DXA and US. Limits of agreement were set at a confidence and
agreement level of 95%. A linear regression analysis was used to investigate proportion
bias related to BIA and US when compared to DXA. All analysis was conducted using the
software Jamovi for Windows, version 2.3.28.
3. Results
Descriptive characteristics of the subjects, as well as the measured BF% from DXA,
BIA and US, are presented in Table 1. The mean BMI showed that the sample was
slightly overweight.
Table 1. Descriptive characteristics of the subjects (mean ± SD), n = 23.
Variable
Mean
SD *
Age (years)
Weight (kg)
Height (m)
BMI (kg/m2 )
DXA BF%
BIA BF%
US BF%
30.1
82.5
1.77
26.3
29.0
24.5
19.4
7.7
14.9
0.05
4.37
8.5
7.5
7.0
* SD: standard deviation. BMI: body mass index. BF%: body fat percentage. DXA: dual-energy X-ray absorptiometry. BIA: bioelectrical impedance. US: ultrasound.
The BF%s derived by BIA and US were highly correlated with DXA when considering
the Pearson correlation coefficient (r = 0.94 and 0.89 for BIA and US, respectively, both
p < 0.001). When considering the concordance correlation derived from simple agreement
analysis, the coefficients were 0.80 for BIA and 0.49 for US. BMI was also highly correlated
with all BF% methods (r = 0.85; 0.93; and 0.84 for DXA, BIA and US, respectively. All
p < 0.001).
3.1. Agreement between DXA and BIA
The concordance correlation coefficient was high for BIA (0.80). Yet, BF% measured by
BIA (24.5 ± 7.5) was on average 4.4% lower than DXA (29.0 ± 8.5). This mean difference
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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ffi
ff
was statistically significant (p < 0.001). The Bland–Altman plot showed very large limits
of agreement between DXA and BIA. The lower and upper agreement− limits were −1.45
− CI −3.70–0.80) and 10.31 (95% CI 8.06–12.56). There was a tendency of BIA to under(95%
estimate BF%, especially among those with higher BF%, as shown by the blue proportional
bias line in Figure 1. Linear regression confirmed this tendency of proportional bias of BIA
(p = 0.09) to underestimate BF% when compared to DXA.
Figure 1. Bland–Altman plot. Comparison between BF% derived by DXA and BIA. Green and salmon
color areas represent the estimate of the upper and lower limit of agreement (dashed line in the center
tt lines at the bottom
tt
is the estimate) with lower and upper confidence intervals (dotted
and top of the
ff
green and salmon area). Lilac color represents the mean difference between methods (dashed line)
tt
tt
with lower and upper confidence intervals (dotted lines at the bottom and top of the lilac color area).
3.2. Agreement between DXA and US
The concordance correlation ffi
coefficient was moderate for US (0.49). BF% measured by
US (19.4 ± 7.0) was on average 9.6% lower than DXA (29.0 + 8.5%). Thisffmean difference
was statistically significant (p < 0.001). The Bland–Altman plot showed very large limits of
agreement between DXA and US. The lower and upper agreement limits were 2.01 (95% CI
−−0.89–4.90) and 17.14 (95% CI 14.25–20.04). The tendency to underestimate BF%, especially
among those with higher BF%, was more pronounced in US, as shown by the proportional
bias line (blue) in Figure 2. Linear regression confirmed this proportional bias tendency of
US (p = 0.057) to underestimate BF% when compared to DXA.
Figure 2. Bland–Altman plot. Comparison between BF% derived by DXA and US. Green and salmon
color areas represent the estimate of the upper and lower limit of agreement (dashed line in the center
tt
is the estimate) with lower and upper confidence intervals (dotted
lines at thettbottom and top of the
green and salmon area). Lilac color represents the mean ff
difference between methods (dashed line)
tt
tt
with lower and upper confidence intervals (dotted lines at the bottom and top of the lilac color area).
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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4. Discussion
This study aimed to investigate the agreement of measurement of BF% obtained by
BIA and US compared to DXA in a group of healthy male college students. The main result
was that, although the methods showed a high correlation, both BIA and US significantly
underestimated BF% compared to the gold-standard reference (DXA). This underestimation
was more pronounced among those with high BF%.
BIA has been widely used in research settings to assess the body composition of
adults [4], older adults [16], people with chronic disease [7] and male and female college
students [17]. There are several BIA devices that are commercially available, and some
were tested for their validity and agreement with gold-standard methods.
Although we did not find a single study testing the BIA model that was used in the
present study, Pribyl, Smith and Grimes [17] analyzed the accuracy of a very similar model
(Omrom HBF-500) within a sample of male and female college students (±25.8 years).
They found that BIA significantly overestimated BF% in males by approximately 1.5%
with tighter agreement limits, while the present study found an underestimation of BF%
by BIA with large agreement limits. However, they compared BIA with air displacement
plethysmography (BOD POD) as the criterion, while this study used DXA as the reference.
So, further comparison is limited. Furthermore, another study with young men compared
BIA devices with BOD POD as the reference and found no significant differences regarding
BF% [18].
Rockamann et al. [10] compared four different BIA devices with DXA in a sample of
male and female college students (±19.8 years). All devices were hand-held. In the present
study, a tetrapolar hand and foot device was analyzed, limiting comparison. Despite that,
they found that two of the four devices underestimate BF% by −3.6 and −5.8% even with
a moderate correlation coefficient (around 0.64), which is similar to the result of the present
study (we found a mean difference of −4.5% with a high correlation).
Just like BIA, US has been used in research and clinical settings for its low cost, ease
of use and transportation [9]. Similar to BIA, a variety of US devices are available, and
some have been considered useful to assess subcutaneous fat tissue [19] and to predict
body fat [14]. Of note, some previous studies investigated the validity of the device that
we used in the present study (BodyMetrix B2000). This device measures the thickness of
the subcutaneous fat layer on specific body sites, which are then used to estimate body
fat. This is analogous to the skinfold protocols proposed by Jackson and Pollock [15]. A
comparison of caliper and US regarding the thickness of subcutaneous fat was performed
previously but was not within the scope of the present work [19].
Johnson and colleagues [12] found that the BodyMetrix B2000 (BMB2000) failed to
agree with DXA when measuring the BF% of male college students (±23.0 years) with a
significant underestimation of −4.4%, even though there was a strong correlation (r = 0.84).
This result is similar to what was found in the present study, but the underestimation
here was even higher, reaching −9.6%, with a moderate concordance correlation of 0.49.
Differences could be related to the fact that the present study used a three-site protocol,
whereas Johnson et al. used a seven-site protocol.
Indeed, the agreement of different BMB2000 protocols may vary. Baranauskas and
colleagues [8] observed significant differences in the BF% of male and female college
students (±22.8 years) between seven-site and three-site Jackson and Pollock protocols,
showing that the three-site BF% was significantly lower than the seven-site. In addition,
both three-site (−5.1%) and seven-site (−3.9%) protocols significantly underestimated BF%
when compared to DXA. Similar to the Baranauskas study, Elsey and colleagues [20] also
found the three-site protocol to underestimate BF% compared to seven-site in a sample of
female athletes.
One study performed a thorough investigation about various BMB2000 protocols in
male college students (±20.0 years) and compared the results to DXA [13]. The authors
observed that the three-site protocol, as used in the present study, showed a strong Pearson
correlation with DXA (r = 0.87). In the present study, the Pearson correlation was very
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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similar (r = 0.89), but the concordance correlation coefficient, which is more adequate to
test agreement between methods, was moderate in the present findings (0.49). Moreover,
Kang et al. [13] observed an underestimation of about −7.0% compared to DXA-measured
BF%, and this was the worst of all nine protocols they evaluated.
Strengths and limitations are recognized in the present study. Firstly, we assessed a
small convenience sample, which may be statistically underpowered. However, a goldstandard method that is difficult to access was used as the reference. Secondly, only one
US protocol was analyzed. However, we chose the three-site protocol due to its alleged
accessibility and suitability in clinical settings. Of note, Jackson and Pollock’s equation
has been validated in Brazilian males [21] and is extensively used in body composition
research in Brazil. Thirdly, only adult men attending college were included, which makes
it impossible to generalize the results to other groups. Noteworthy, this study analyzed
a BIA device that was not analyzed before (to the best of our knowledge). Finally, there
were no specific instructions regarding hydration or fasting before the measurements, as
the sample was acquired through convenience. This may introduce bias to comparison
with other studies. Yet, it is important to mention that this approach mirrors a commercial
setting, where participants typically arrive without prior instructions concerning exercise
and food and water consumption.
5. Conclusions
In summary, BIA and US have been considered effective alternatives to the expensive
and technical DXA technique [12]. However, these methods also require practical device
operation skills and proper training before the examination, especially US, because of
details like proper probe positioning [22]. In the present study, both devices showed to be
inaccurate to estimate BF% compared to DXA, even though they presented moderate to
high correlation. This inaccuracy was higher in individuals with higher BF measured by
DXA. Underestimation and proportional bias were more pronounced in the US method.
These results are consistent with the previous literature. Therefore, the risk of (mis)interpretation and bias is clear and may potentially impact nutritional and physical activity
planning in clinical settings [23]. BF% underestimation may supposedly lead to accommodation and lack of engagement in nutritional and physical activity programs among healthy,
overweight and obese people. So, it is possible that simple and inexpensive methods of
BF% assessment may negatively interfere in BF monitoring [10].
Future studies should continue to investigate the validity and agreement between new
body composition devices and reference methods with diverse and larger samples, as body
composition monitoring is essential in health and many disease contexts.
Author Contributions: Conceptualization, M.O. and M.D.; methodology and data collection, M.O.;
V.C.L., M.A.D. and G.R.; formal analysis, M.D.; data curation, M.O. and M.D.; writing—original
draft preparation, M.D.; writing—review and editing, M.O., V.C.L., M.A.D. and G.R.; supervision,
M.D.; funding acquisition, M.D. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by the Research Support Foundation of the Federal District,
Brazil (FAPDF), and the APC was funded by the Research Support Foundation of the Federal District,
Brazil (FAPDF). Process number 00193-00002310/2022-26.
Institutional Review Board Statement: The study was conducted in accordance with the Declaration
of Helsinki and approved by the Ethical Committee of the Brasilia Higher Education Center (IESB)
under the protocol nº 6.812.917 on 9 May 2024 for studies involving humans.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: Data are contained within this article.
Conflicts of Interest: The authors declare no conflicts of interest. The funders had no role in the design
of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; or
in the decision to publish the results.
J. Funct. Morphol. Kinesiol. 2024, 9, 113
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