ELBOW FLEXION AND EXTENSION MOVEMENTS
CHARACTERIZATION BY MEANS OF EMG
L. M. Bittar and M. C. F. Castro
Centro Universitário da FEI, Electrical Engineering Department, Av. Humberto A. C. Branco, 3972
São Bernardo do Campo, CEP 09850-901, Brazil.
Keywords: Electromyography, Biceps, Triceps, Elbow, Flexion, Extension.
Abstract: Electromyographic (EMG) signal is the electrical manifestation of neuromuscular activation associated with
muscle contraction. The present work intends to characterize the behavior of the muscles biceps and triceps
during elbow flexion and extension movements, without load. These movements were performed at
horizontal and vertical planes. Three types of test were performed, for each plane, relating EMG signal with
joint position. Five men volunteers, ages ranged between 18 and 21 years old, were selected to participate to
the tests. The first test consisted to move 10 degrees for each three seconds until the allowed maximum
flexion and then, to return at the same way to the initial position. For the second test, the same movement
was made but continuously, without stopping at intermediate positions. And for the third test, continuously
flexion and extension movements were repeated sequentially but for different amplitudes, increasing by 10
degrees each. The tests were repeated, three times each. Initially, graphical analysis of the data was made
for standard behavior detection and, for a quantitative analysis, after EMG preprocessing, averages and
variation coefficients were calculated from specific intervals at the beginning, middle and at the end of
movement. Although an EMG signals inherent variability, results showed inter and intra subject's
repeatability, but only for movements performed at the horizontal plane.
1 INTRODUCTION
The general mechanism of muscle contraction, under
voluntary control, involves the following processes:
- stimulation of motor nerve by a neuronal action
potential;
- secretion of neurotransmitter (acetylcholine) at
the neuromuscular junction;
- propagation of a muscular action potential
through the muscular fiber;
- ionic flow across the muscle membrane;
- contractile process itself (Guyton, 2002;
Capucho, 2005).
The basic unit of the muscle is named motor unit
and it is constituted by a motor neuron and all
muscular fibers innervated by this neuron. The
electrical signal that is detectable by each unit is
named Motor Unit Action Potential (MUAP), and
this constitutes the fundamental unit of
Electromyographic (EMG) signal. The EMG signal
is the electrical manifestation of neuromuscular
activation associated with a muscle contraction, it is
accessible at the body surface and it can be used for
different purposes, as neuromuscular disease
diagnoses, rehabilitation process evaluation and also
to analyze muscle behavior performing specific
movements.
The surface EMG signal amplitude ranged from 0
to 10 mV peak-to peak or from 0 to 1,5 mV rms, and
frequency ranged from 0 to 500 Hz, with dominant
energy between 50 and 150 Hz (DeLuca, 2002), but
deterministic characteristics were during the initial
200 ms of the muscle contraction (DeLuca, 1979).
EMG signal detection and acquisition process
need some caution due to several factors that can
affect the results. The electronic apparatus used, the
environment, the electrodes and the movement of
the electrodes during the tests can introduce noise.
This interference can be avoided or eliminated by
using:
- differential electrode configuration and
differential amplification;
- position of the electrodes on the midline of the
muscle belly;
- rms value of the signal, for measuring the
amplitude of the voluntarily elicited EMG signal
147
M. Bittar L. and C. F. Castro M. (2008).
ELBOW FLEXION AND EXTENSION MOVEMENTS CHARACTERIZATION BY MEANS OF EMG.
In Proceedings of the First International Conference on Biomedical Electronics and Devices, pages 147-150
DOI: 10.5220/0001048801470150
Copyright
c
 SciTePress

(consists to rectify and integrate the signal in
data time interval) (DeLuca, 2002).
2 MATERIAL AND METHODS
Five men volunteers, ages between 18 and 21 years
agreed to the test procedures, aiming to evaluate the
contribution of biceps and triceps muscles during
voluntary flexion and extension elbow movements,
without load. For the accomplishment of the tests, a
device for
arm support and joint angle monitoring
was used. The right arm were accommodated
and
fixed, allowing free elbow movement in only one
plane and hindering other movements. For EMG
signal acquisition, surface electrodes and the
Powerlab PTB300 kit from ADInstrumets were
used.
Figure 1: Device for arm support and joint angle
monitoring.
The procedure consisted of three types of tests
that would have to be repeated three times each for
both horizontal and vertical planes.
Test 1: The volunteer had to move 10 degrees
every 3 seconds, initiating in total extension and
finishing with maximum flexion of 90 degrees, for
the horizontal plane and 70 degrees for the vertical
plane, and then had to return, to the initial position,
by the same way.
Test 2: The volunteer had to repeat the amplitude
of previous movement, but varying the joint position
continuously, with controlled speed of 10 degrees
for second, without stopping in the intermediate
positions.
Test 3: The volunteer had to repeat several times
elbow flexion/extension, but each
time, amplitude
movement was increased by 10 degrees. The initial
amplitude was 10 degrees and the final amplitude
was 90 degrees, for the horizontal plane and 70
degrees for the vertical plane.
The archives with the signal waveforms,
obtained during the tests, were used for the result
analysis, making possible the detection of standard
behaviors. For the quantitative analysis, specific data
intervals were fixed, considering beginning, middle
and the end of movement, covering joint angles for
extension and flexion positions. For these data sets,
the mean and the variation coefficient were
calculated for each one of the repetitions and among
the three repetitions made by the same volunteer.
3 RESULTS
3.1 Movements at Horizontal Plane
Figure 2: Arm position during movement at horizontal
plane.
Figure 3 shows the signals acquired with one
volunteer. From the top to the bottom, the first is the
trigger signal for movement synchronism and speed
control, joint angle position, biceps EMG signal,
triceps EMG signal, rms of biceps EMG signal, rms
of triceps EMG signal. And the columns represent
each one of the repetitions of each of the three tests.
Figure 3: Waveforms obtained from the movements at
horizontal plane with one volunteer.
Tests 1 and 2 showed that triceps acted more at
the beginning and at the end of the movement, with
BIODEVICES 2008 - International Conference on Biomedical Electronics and Devices
148

the arm around extension position (joint angle
varying from 0
o
to 10
o
and from 10
o
to 0
o
), while
biceps acted more at the central part of the
movement, between the peaks of triceps
performance (around 90
o
of flexion). Test 3 showed
a quite constant intensity on triceps recruitment
during movements, independently of the joint angle
and movement amplitude. On the other hand, biceps
signal showed an intensity increase as the amplitude
of the movement increased.
In all the movements performed at the horizontal
plane, for both muscles, were found a standard
pattern at the values obtained from different
volunteers, making possible the determination of
representative means values as shown in table 1. The
values were in accordance with the qualitative
results presented before.
Table 1: Mean values obtained during muscle contraction
from movements performed at horizontal plane (µV). (B.-
Biceps; T. -Triceps).
Position
Test 1 Test 2
Amplitude
Test 3
B. T. B. T.
B. T.
Beginning
0
o
–10
o
Extension
1,5 3,7 1,3 3,72
Small
0
o
– 10
o
1,29 3,75
Intermediate
40
o
–50
o
Flexion
1,71 3,26 1,72 3,21
Intermediate
0
o
– 40
o
1,43 3,54
Middle
80
o
–90
o
Flexion
3,5 3,16 3,1 3,12
Intermediate
0
o
– 50
o
1,5 3,6
End
10
o
–0
o
Extension
1,8 4,47 1,75 4,83
Maximum
0
o
– 90
o
1,88 3,58
3.2 Movements at Vertical Plane
Tests 1 and 2 showed that the biceps had a large
contribution during all the movement, but it was
more requested at the beginning and at the end of the
movement. Triceps acted a little more at the
beginning of the movement, but its EMG signal was
practically constant. In test 3, EMG signal was
practically constant for both muscles, but the biceps
EMG signal showed a greater intensity.
Figure 4: Arm position during movement at vertical plane.
Figure 5: Waveforms obtained from the movements at
vertical plane with one volunteer.
In the movements performed at the vertical plane
there were no intensity pattern among volunteers for
biceps recruitment as verified at horizontal plane.
This indicates that each volunteer requested the
muscle of different manner for the accomplishment
of the same movement. By the other side, EMG
signal from the triceps showed a standard pattern,
making possible the determination of representative
mean values as shown in table 2.
Table 2: Mean values obtained during muscle contraction
from movements performed at vertical plane (µV). (B.-
Biceps; T.- Triceps).
Position
Test 1 Test 2
Amplitude
Test 3
B. T. B. T.
B. T.
Beginning
0
o
–10
o
Extension
--- 4,17 --- 3,81
Small
0
o
– 10
o
--- 4,11
Intermediate
30
o
–40
o
Flexion
--- 3,25 --- 3,31
Intermediate
0
o
– 30
o
--- 3,88
Middle
60
o
–70
o
Flexion
--- 2,98 --- 3,04
Intermediate
0
o
– 40
o
--- 4,14
End
10
o
–0
o
Extension
--- 3,32 --- 3,68
Maximum
0
o
– 70
o
--- 4,18
4 DISCUSSION
Since the biceps acts for the flexion movement while
the function of triceps is related with the elbow
extension, the data obtained are consistent with the
expected.
At the horizontal plane, EMG signal from the
triceps had greater intensity at the beginning
and at
the end of the movement (intervals from 0º to 10º
and from 10º to 0º). During these
phases, the arm
was at an extended position or near of it, needing to
surpass the inertia of the movement. At the
intermediate flexion position the contribution of the
ELBOW FLEXION AND EXTENSION MOVEMENTS CHARACTERIZATION BY MEANS OF EMG
149

triceps decreased while the contribution of the
biceps increased, but even so the biceps EMG signal
remained smaller than the triceps EMG signal. This
situation changed at half of the movement, where the
elbow was in a full flexed position, requesting more
of the biceps.
On the other side, for the movements performed
at the vertical plane, EMG signal from the biceps
showed greater intensity at the beginning and at the
end of the movement (intervals from 0º to 10º and
from 10º to 0º). The gravity influence is greater over
the biceps at this plane. To surpass inertia the
requested muscle was not triceps, as verified at the
horizontal plane, but it was the biceps. Quantitative
analysis showed that the intensity of EMG signal of
the triceps was quite constant at this plane.
Aiming to quantify the variability of data sets
during the movement and among each repetition
made by the same volunteer, coefficients of
variation were calculated. According to Araújo
(2000), the coefficient of variation from the EMG
signal is very high, being around 21.61% the
average of variation of that parameter. It means that
values around 20% do not indicate, necessarily,
different muscular activities. This high variation can
be caused by factors as position and quality of the
electrodes, change of temperature and changes in the
metabolism.
The coefficients of variation values obtained
from the tests performed at the horizontal plane were
around 25%. Therefore, it can be considered that
there was repeatability of the movements performed.
Moreover the repeatability inter the several
movements executions made by the same volunteer,
the existence of a standard pattern of EMG
intensities for both muscles, certify that there is a
repeatability intra volunteers and also the existence
of a recruitment pattern.
Analyzing the coefficients of variation obtained
from the movements performed at vertical plane, the
values related with the triceps were around 25%,
indicating the same pattern analyzed previously. By
the other side, although the coefficients related with
the biceps, for each repetition was small, indicating
little variation during the test, the values between
repetitions were around 35%, indicating that there
was no repeatability among recruitment for each
movement performed by the same volunteer. There
were cases with coefficients above 50% that
probably were related with some isolated stronger
muscular contraction made during the test. At
vertical plane it was not possible to identify a
recruitment pattern due to the variability of the data.
Besides that, it was observed small
displacements of electrode positions during
movements, and it must be
also considered
interference due the signals of adjacent muscles.
These comments are in accordance with verified by
DeLuca (1997), in other experiments.
5 CONCLUSIONS
During the tests, the muscle triceps showed a quite
constant behavior, with repeatability of movements
at both planes. The muscle biceps demonstrated this
behavior only for movements performed at the
horizontal plane, in which it had a little recruitment.
For movements performed at the vertical plane, the
biceps was more requested, resulting in a greater
intensity EMG signal, but without repeatability.
There are several factors that can disturb EMG
signal, but despite of the interference, it is possible
to characterize movements by means of EMG,
showing the intensity of muscle recruitment.
The results showed the existence of a recruitment
pattern for biceps and triceps among different
subjects but only for movements performed at the
horizontal plane.
ACKNOWLEDGEMENTS
The authors would like to thank FAPESP and FEI
support.
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