ADIPSMETER

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.

1 INTRODUCTION

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

application.

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

recording.

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

174

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.,

2010).

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.

2 INTEGRATED SYSTEM

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

environments.

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

175

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

printed.

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

protocol.

3 MAIN CHARACTERISTICS

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

clamps.

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

calliper.

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

Measurement

range

0 - 80 mm 0 - 110 mm

Resolution 0.2 mm 0.07 mm

Pressure

10 gf/mm

>25 % variation

10 gf/mm

<5% variation

Type of

reading

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

5%.

Table 2: Comparative study of the error in pressure.

Harpenden Adipsmeter

Pressure

(gf/mm

)

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

pressure

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%

4 SYSTEM PERFORMANCE

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

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measuring biceps, triceps, subscapular and iliocristal

skinfolds.

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

sample.

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

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

(1)

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

callipers.

5 FINAL COMMENTS

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.,

2010).

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