A New Skinfold Calliper System
Maria de Fátima Chouzal, Maria Teresa Restivo, Manuel Rodrigues Quintas
Carlos Moreira da Silva, Tiago Andrade and Maria Teresa Amaral
IDMEC - Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
Keywords: Body fat percentage, Skinfold calliper, Digital sensing, Wireless data communication, Mechanical device,
Automated process.
Abstract: Nowadays, the assessment of body composition is of great meaning but traditional skinfold callipers
recognized in the nutritional area have not been technologically updated to provide a more effective
performance with greater accuracy, allowing automatic data processing and recording in a database, offering
a more user friendly handling not requiring technicians with a high degree of expertise. In order to
overcome many of these deficiencies a new instrument named Adipsmeter was designed and developed. A
new mechanical skinfold calliper structure has been digitally instrumented for reading skinfold thickness
and equipped with wireless communication capabilities with a personal computer where a software
application, integrating a database, is installed and prepared for driving a technician along a specific
protocol incorporating many regression equations used in current body fat measurement at an affordable
price. Its measurement range is from 0 to 110 mm, consistent with a range of use from children to obese
individuals. Between the two opposing clamping surfaces mounted on its rigid arms the pressure has a
constant value of 10 gf/mm
in the whole measurement range. It has small dimension and weight and while
being robust provides comfortable handling. The sensing system resolution is less than 0.1 mm, the wireless
communication (MiWi) is suitable for healthcare environments, with 25 h of autonomy. The software
application, with an intuitive and user friendly interface, is based in Visual Basic 2008.
Nowadays, the assessment of body composition by
estimating the percentage of body fat (%BF) has a
great impact due to the constant demand from the
World Health Organization (European Parliament,
2008) in order to combat obesity, now considered
the twenty-first century disease.
The measurement of skinfold thickness using a
skinfold calliper is a simple, non-invasive and cost-
effective method for assessing body composition
(Jackson et al., 2009), recognized in the nutritional
area as an expeditious, portable and affordable tool.
However, the traditional skinfold calliper
available in the market does not take advantage of
today´s technology in order to provide more
effective assessment with greater accuracy, allowing
automatic data processing and recording in a
database, offering a more user friendly handling not
requiring technicians with high degree of expertise.
In order to overcome many of these problems a new
instrument named Adipsmeter was designed and
developed, consisting in a skinfold calliper
electronic instrumented structure and a software
Initially, some amendments were done to the
mechanical support of a Harpenden skinfold calliper
in order to integrate digital sensing and a wireless
communication system with a software application
developed in LabVIEW (Restivo et al., 2009,
Restivo et al., 2010).
This sequential test procedure application helps
technicians with low level of expertise, not requiring
reading or mental time counting always subjective
(Norton and Olds, 1996), increasing test efficiency
and quickness. Moreover, it immediately processes
data using many regression equations allowing its
The performance of this equipment has been
compared with that of a traditional Harpenden and
also validated against the reference Dual-energy X-
ray Absorptiometry system (DXA). A significant
de Fátima Chouzal M., Teresa Restivo M., Rodrigues Quintas M., Moreira da Silva C., Andrade T. and Teresa Amaral M..
ADIPSMETER - A New Skinfold Calliper System.
DOI: 10.5220/0003140101740178
In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 174-178
ISBN: 978-989-8425-37-9
2011 SCITEPRESS (Science and Technology Publications, Lda.)
agreement in the assessment of body composition
was found in a sample of 40 adults (Amaral et al.,
In spite of the important features of this skinfold
calliper solution, problems related with mechanical,
handling and ergonomic caracheristics still existed.
Also the wireless communication protocol was not
the most suitable for health care environments. Due
to the inherent characteristics of the Harpenden
structure the skinfold calliper force between clamps
did not remain constant for the whole measurement
range (42% variation) and the clamps stiffness did
not allow them to remain parallel, specially for
higher skinfold thickness.
For solving all the mechanical weaknesses
inherent to the Harpenden skinfold calliper a new
structure has been carefully designed.
The main goal of the Adipsmeter prototype
development has been to create an advanced
digitally instrumented skinfold calliper for reading
skinfold thickness, capable of wireless
communication with a personal computer software
application, integrating a database.
This integrated system for assessing body
composition, the Adipsmeter, consists of a software
application, LipoSoft-2010, and a mechanical
device, a skinfold calliper specially designed to
interact with such an application and to provide
better technical characteristics than those available
in the market.
2.1 Mechanical Device
The mechanical device comprises basically a closed
cylindrical body and a structure of two jaws
terminated by mechanically oriented clamps,
manipulated by a handle and a lever, Figure 1.
Figure 1: The mechanical device.
The cylindrical body includes all the mechanical
elements of constant force transmission to the jaws,
the sensing element, the interaction buttons, the
battery and all the electronics.
The handle has passive return through a
transmission chain ensuring a nearly constant
pressure between clamps of about 10 gf/mm
for the
whole measurement range which at present goes up
to 110 mm allowing its use in obese individuals. But
the mechanical solution developed allows this
measurement range to be further increased without
losing the mechanical performance. The devices in
the market offer a limited measurement range, below
80 mm.
A mechanical rotating mechanism keeps the
parallelism between the clamps faces for any jaw
opening angle.
The electronic system integrates a battery
charging system, the conditioning signal and a
dedicated microcontroller. It also enables wireless
communication with the LipoSoft-2010 application.
The microcontroller is responsible for managing the
entire device. Interaction with the application is
performed with buttons in the device body. The
electronics energy consumption has been optimized
and the device offers 25 hours autonomy.
Compared to the skinfold callipers available in
the market this device is a medium size, lightweight
and handling balanced. Its design symmetry allows
easy use by left handed technicians.
2.2 Digital Sensing
and Communication
For measuring skinfold thickness a rotary
incremental encoder is used. The jaws rotating angle
is multiplied by five.
The encoder provides two quadrature channels,
each with 500 pulses/revolution. Since the maximum
jaw opening (110 mm) is equivalent to a 250°
rotating angle, the skinfold measurement resolution
is 0.07 mm.
The wireless communication system uses a
MiWi protocol, suitable for health care
The measurement resolution and the data
transfer rate are suitable for future studies of
dynamic tissue behaviour.
2.3 Software Application LipoSoft2010
The software application LipoSoft-2010, developed
in Visual Basic 2008, offers a user friendly graphical
interface suitable to be used by technicians without
high training level, Figure 2.
ADIPSMETER - A New Skinfold Calliper System
A database integrated with the application allows
the searching of individual files and data updating,
as well as the registration of any new individual.
A body image is also presented and helps to clarify
the body location of the chosen skinfold under
Figure 2: The LipoSoft-2010 application.
measurement, for any of them. When the
measurement procedure is finished, by using any of
the available methods, this image is also used for
giving a pictorial idea of the percentage of the
individual body fat composition evaluation by using
the colour associated to the established %BF levels.
A final assessment report can be generated and
The software application allows an easy
inclusion of new features, such as regression
equations or any other developed algorithm. It can
be used as a training tool by guiding the user
through the established procedure and allowing the
step-by-step progress along the measurement
The new mechanical design, the improved sensing
system and the communication solution give to
Adipsmeter better technical features, which
combined with its easier use, make it a very
competitive device.
The measuring range of 0 to 110 mm allows
obesity evaluation with constant pressure between
The sensing system presents an overall
measurement resolution of 0.07 mm. The MiWi
system for wireless communication is suitable for
healthcare environments. The device autonomy is of
25 h.
This skinfold calliper presents a medium size
dimension and offers robustness, easy handling and
lightweight. Its configuration is adequate for both
right- and left-handed users. The production cost is
low, definitely below that of the Harpenden skinfold
Table 1 summarizes the main characteristics of
this integrated system, Adipsmeter, in comparison to
those of the traditional Harpenden skinfold calliper.
Table 1: Some characteristics of Harpenden and
Adipsmeter skinfold callipers.
Harpenden Adipsmeter
0 - 80 mm 0 - 110 mm
Resolution 0.2 mm 0.07 mm
10 gf/mm
>25 % variation
10 gf/mm
<5% variation
Type of
Analogue Digital
Material Metal Metal
Weight 475 gf 340 gf
Cost 700 £ < 500 €
Although the 10 gf/mm
pressure value between
clamp surfaces has been consistently found in the
literature as a standard for the measurement protocol
and so referred as a characteristic for all skinfold
callipers available in the market, this pressure value
is far from being kept constant throughout the whole
measuring range for the Harpenden calliper.
The tests, reported in Table 2, show that the new
mechanical device respects this pressure standard
and maintains the 10 gf/mm
value throughout its
extended measurement range with an error below
Table 2: Comparative study of the error in pressure.
Harpenden Adipsmeter
0-40 mm 6.7 – 7.9 9.8 – 10.2
40-80 mm 5.0 – 6.6 9.8 – 10.2
80-110 mm -- 10.2 – 10.3
Total range 5.0 – 7.9 9.8 – 10.3
Error in
0-40 mm 17.0% 3.6%
40-80 mm 27.5% 3.6%
80-110 mm -- 1.2%
Total range 45.6% 4.8%
The performance of this new system was evaluated
in a first instance, using a sample of 14 adults, aged
from 19 to 26 years. Both callipers, traditional
Harpenden and Adipsmeter, were used for
BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices
measuring biceps, triceps, subscapular and iliocristal
The body density was estimated using the
equations of Durnin & Womersley (Durnin and
Womersley, 1974) and the %BF was estimated using
the equation of Siri (Siri, 1961). Table 3 presents the
statistical data corresponding to the respective
Table 3: Characterization of the sample (n =14)
Age (years) 21.36 ± 4.80
Height (m) 1.64 ± 1.33
Weight (kg) 59.60 ± 8.01
Original Harpenden BF (%) 27.94 ± 5.49
Adipsmeter BF (%) 28.26 ± 5.52
Adipsmeter - Harpenden (%) 0.31 ± 0.58
Mean values ± standard deviation.
A strong association between the values of the
%BF, calculated by the equation of Siri, with
skinfold measurement made with both the original
Harpenden skinfold calliper (%BF Harpenden) and
with the Adipsmeter (%BF Adipsmeter) was
achieved (r = 0.996). The slope of the regression line
is near the unit (0.999), corroborating the agreement
between these two variables, Figure 3.
y = 0,9994x + 0,3312
= 0,992
0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 40,00
%BF Harpenden
%BF Adipsmeter
Figure 3: Percent body fat (%BF) measured by Harpenden
and by Adipsmeter linear relationship. (—) linear fit line.
In this study, the value of SEE (standard error of
the estimate) (0.58) is ideal according to the existing
bibliography indicating that SEE must be less than
3% for a new method to be accepted as accurate
(Lohman, 1996).
It is also reported in the literature that the total
error, TE, can be calculated as:
= nyyTE
where y
and y
are the values measured by
Harpenden and Adipsmeter, respectively) is the best
parameter for evaluating differences between two
measures (Lohman, 1992). In our study, TE is 0.31,
indicating a very high level of agreement between
the measurements obtained by the two skinfold
The integrated system Adipsmeter, due to its
mechanical design, presents better technical
characteristics, namely an extended measurement
range, a near constant pressure between clamp
surfaces for the whole measurement range, better
handling and lighter weight. Its electronics provides
also a better resolution and a suitable wireless
protocol for health environments.
The automatic task procedure during
measurement significantly reduces evaluation
subjectivity and considerably increases the checking
task efficiency, offering graphical information of the
%BF individual level.
Nevertheless, new developments are now being
prepared for improving even further the novel
skinfold calliper performance. Since the rate and
resolution of the data transfer are suitable for studies
of tissue dynamics, the main idea is to explore the
dynamic response of subcutaneous tissues when
subject to a compression effect in order to better
characterize the body composition.
Furthermore it is within one of the main
objectives to take advantage of current techniques
such as artificial neural networks as well as the
Adipsmeter capabilities for developing new
algorithms for data processing (Barbosa et al.,
Amaral, T., Restivo, M. T., Guerra, R., Marques, E.,
Chousal, M. F., Mota, J. (2010). Validation of a digital
skinfold system for estimating body fat based on
skinfold thickness measurement. Accepted to the
British Journal of Nutrition.
Barbosa, M. R., Amaral, T., Chouzal, M. F., Restivo, M.
T. (2010). Neural Networks Based Approach to
Estimate Body Fat (%BF). In Controlo2010, 7-10
September, Coimbra Portugal.
Durnin J. V., Womersley J. (1974). Body fat assessed
from total body density and its estimation from
skinfold thickness: measurements on 481 men and
women aged from 16 to 72 years. British Journal of
Nutrition; 32(1):77-97.
European Parliament. (2008). European Parliament
Resolution of 25 September 2008 on the White Paper
ADIPSMETER - A New Skinfold Calliper System
on nutrition, overweight and obesity-related health
issues (2007/2285(INI)) P6_TA(2008)0461.
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equations with diverse young men and women: the
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BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices