Performances Comparison of EMG Signal Analysis for Manual Lifting using Spectrogram

Abstract

Electromyography (EMG) signal is non-stationary signal and highly complex time and frequency characteristics. Fast-Fourier transform common technique in signal processing involving EMG signal. However, this technique has a limitation to provide the time-frequency information for EMG signals. This paper presents the analysis of EMG signal of the variable lifting height and mass of load between the four subjects selected in manual lifting by using spectrogram. Spectrogram is one of the time-frequency representation (TFR) that represents the three-dimensional of the signal with respect to time and frequency in magnitude presentations. The manual lifting tasks is based on manual lifting of 5 kg and 10 kg load that performed by the right biceps brachii at lifting height of 75 cm and 140 cm. Four from ten healthy volunteers in fresh condition is selected into this comparison of subject performance tasks with their raw data collections. The raw data of EMG signals were then analyzed using MATLAB 2011 to obtain the voltage in time and frequency information. This study obtained the mean instantaneous RMS Voltage (Vrms(t)) to visualize the strength of the subjects produced during the manual lifting tasks. Results of this study evince the physical details of the subjects would able to effect the performance of the lifting. Higher lifting height and the number of contraction, the better performance of the subjects. It concluded that the application of spectrogram is able to providing the performance of the subjects by time-frequency information for EMG signals.

Full text

ISSN: 2180-1843 e-ISSN: 2289-8131 Vol. 8 No. 7 29
Performances Comparison of EMG Signal Analysis
for Manual Lifting using Spectrogram
T. N. S. T. Zawawi, A. R. Abdullah, E. F. Shair, S. M. Saleh
Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka,
76100 Durian Tunggal, Melaka, Malaysia.
tgnorshuhadatgzawawi@gmail.com
Abstract—Electromyography (EMG) signal is non-stationary
signal and highly complex time and frequency characteristics.
Fast-Fourier transform common technique in signal processing
involving EMG signal. However, this technique has a limitation
to provide the time-frequency information for EMG signals. This
paper presents the analysis of EMG signal of the variable lifting
height and mass of load between the four subjects selected in
manual lifting by using spectrogram. Spectrogram is one of the
time-frequency representation (TFR) that represents the three-
dimensional of the signal with respect to time and frequency in
magnitude presentations. The manual lifting tasks is based on
manual lifting of 5 kg and 10 kg load that performed by the right
biceps brachii at lifting height of 75 cm and 140 cm. Four from
ten healthy volunteers in fresh condition is selected into this
comparison of subject performance tasks with their raw data
collections. The raw data of EMG signals were then analyzed
using MATLAB 2011 to obtain the voltage in time and frequency
information. This study obtained the mean instantaneous RMS
Voltage (Vrms(t)) to visualize the strength of the subjects
produced during the manual lifting tasks. Results of this study
evince the physical details of the subjects would able to effect the
performance of the lifting. Higher lifting height and the number
of contraction, the better performance of the subjects. It
concluded that the application of spectrogram is able to
providing the performance of the subjects by time-frequency
information for EMG signals.
Index Terms—Electromyography (EMG) Signal; Manual
Lifting; Spectrogram.
I. INTRODUCTION
Today, from the worldometers info, there are 7.3 billion
population in the world is estimated, with 3.1 billion number
of workers working in more than 55 major industrial sectors
[1]. In order providing job opportunities, a large number of
workplaces in the industrial sectors may lead to occupational
injuries if there is no awareness or concern regarding
occupational health and safety [1] and [2]. The National
Institute for Occupational Safety and Health (NIOSH)
recognized the growing problem of work-related back injuries
and published Work Practices Guide for Manual Lifting [3].
Manual lifting is commonly practiced by workers in
industrial workplace to move or transport good to a desired
place. In manual lifting, skeletal muscles perform a crucial
function to execute the task [4]. It is important to handle a
suitable load mass and lifting height to ensure the muscles
work in good experienced fatigue. Muscle performance is the
muscle’s endurance capability before the muscle experienced
fatigue [4].
Electromyography (EMG) signal have been widely used and
applied as a control signal in numerous man-machine interface
applications. It also been deployed in many clinical and
industrial applications [5]. The EMG is known as biomedical
signal that consist of electrical current that generated during
contraction and relaxation phase of muscles [6] and [7].
EMG signal is complicated and non-stationary signal with
highly complex time and frequency characteristics which is
controlled by nervous signal because it always responsible the
muscle activity [7] and [8]. This signal acquires noise and
distorts the signal while travelling through different tissues
during collection and recording process [6] and [9].
A lot of studies have been done based on EMG signal
investigation especially in extraction of EMG signal [10].
Previous researchers used fast Fourier transform (FFT) to
analyze the EMG signal, but it has the limitation to cater non-
stationary signals whose spectral characteristics change in
time [11]. It is no appropriate to use for non-stationary signal
as EMG. It only give the frequency information. Wavelet also
is common used in EMG, however it required more time to
analyze and required to find mother wavelet for each data. It is
also sensitive to noise while EMG produced noise while
travelling to each tissue [8], [9] and [12]. Besides that, to
extract the features, it involved high computational burden. By
artificial Intelligence (AI), it is higher complexity compared to
fast-Fourier transform and Wavelet [13]. Between all of this
common techniques in EMG signal processing, it is show that
Spectrogram with less complexity, better time and frequency
resolution and higher accuracy in order to get the information
from manual lifting activities.
In this research work, time frequency distributions (TFDs)
which are spectrogram employed to analyze the performance
of EMG signal for contraction of muscle activities. This
technique is one of the time-frequency representations (TFR)
that represent a three dimensional of the signal energy with
respect to time and frequency [14]. It is able to have superior
accuracy in challenging task colour modeling [15]. An
optimum frequency resolution is useful for extracting features
of any signals for further analysis included Electromyography
(EMG) signals [16]. From spectrogram, the overall
performance of the different mass of load, height and phase
angle would be known.

Journal of Telecommunication, Electronic and Computer Engineering
30 ISSN: 2180-1843 e-ISSN: 2289-8131 Vol. 8 No. 7
II. METHODOLOGY
A. Flow of data processing
Figure 1 shows the flow of the data collection and how the
data is processed to get the performance of EMG signal for the
contraction of muscle activity.
Figure 1: Flow of the data process
B. Subject Selection
Ten volunteers, five male and five female in healthy
conditions with no previous injuries participated in the
experimental work. G power application is an important
technical assumption for normality assumption for good
estimate the size of sample [17] and [18]. The number of
subjects was calculated using G power analysis software to
determine sufficient EMG raw signals for the analysis process.
Tens subjects selected based on the number of G Power
proposed between the age range of 22 to 25 years was selected
because this age range is commonly available in the
industries[1]. All subjects are right handed. The demographics
of the subjects is shown in [19]
C. Data Collection and Electrode Placement
The raw EMG data collection is measured by using surface
EMG (TeleMyo 2400T G2, Noraxon, USA) and MyoResearch
XP Master Software (Noraxon, USA). The electrode
positioning is at the right biceps. The details of the data
collection and electrodes placement is based on the previous
paper [20].
D. Manual Lifting Experiment
The subjects have to lift a 5 kg and 10kg load with a neutral
body twist (0º) – symmetric lifting with the lifting height
75cm. The subject must repeat the lifting until achieve the
muscle fatigue for five times of repetition. Each lifting
produced EMG signals of contracted muscle, and each EMG
signal was divided into four phases as illustrated in the paper
[19] and [21]. At the Phase 1, the subject holds the load
(located on the floor). At Phase 2, subject lifts the load and put
it on the shelf, then Phase 3, subject arranges the load properly
on the shelf. Lastly, subject release the load at Phase 4.
III. EMG SIGNAL ANALYSIS TECHNIQUES
Spectrogram is used in this EMG signal processing because
it acquire to display the required information in EMG signal.
This is because FFT would not able to display the information
needed because of the limitation to non-stationary signals [22].
The details about spectrogram are already discussed in [19]
and [20]. The equation of the spectrogram is as followed:
2
2
( , ) ( ) ( )
xjf
S t f h w t e d

  





(1)
Instantaneous RMS voltage is extracted from spectrogram to
display the pattern of the signal of instantaneous value Vrms(t)
for the contraction of muscle activities behavioral. Vrms(t) can
be calculated using Equation (2) below [11]:
fmax
rms x
0
V (t)= S (t, f)dt

(2)
where Sx(t,f) is the time-frequency distribution and fmax is the
maximum frequency of interest.
IV. RESULTS AND DISCUSSION
The results of the EMG signal analysis are divided into
some parts to make it clearer presentation to know the
relationship between the different subjects and the
performance of the manual lifts.
A. EMG Signal of Manual Lifting
There are four parameters is considered in this experiment
for four subjects. Figure 2 until Figure 5 shows the example of
raw data for 75 cm and 140 cm lifting height with 5 kg and 10
kg load of mass. The maximum voltage for 5 kg 75 cm is
0.8x10-3 V and the minimum is 0.4x10-3 V with 36 times of
liftings. It is increasing peak voltage due to the increasing of
height with1.3x10-3 V maximum and minimum 0.6x10-3 V at
5 kg, 140 cm for 23 times of lifting.
Due to the Figure 4 (21 times lifting) and 5 (13 times
lifting), it is shown the raw data of manual lifting of 10 kg 75
START
Introduction (Literature review)
Data Collection- Manual lifting task
by TeleMyo 2400T G2, Noraxon,
USA and MyoResearch XP Master
Software (Noraxon, USA)
Data of EMG Signal
Linear Time-Frequency Distribution
Analysis
Time-Frequency Representation
Signal Parameter
END
Spectrogram

Performances Comparison of EMG Signal Analysis for Manual Lifting using Spectrogram
ISSN: 2180-1843 e-ISSN: 2289-8131 Vol. 8 No. 7 31
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 105
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2x 10-3
Sample (N)
Voltage (V)
RAW Signal (10kg, 140cm)
cm and 10 kg 140 cm. Their maximum for both parameters is
1.2x10-3 V and 1.4 x10-3 V while the minimum peak voltage is
1.1x10-3 V. Based on all the figures, it validates that the mass
of the load and the height of the lifting would able to affect the
peak value produced by the subjects.
Figure 6: RAW EMG signal for 5kg, 75cm
Figure 2: Raw EMG signal for 5 kg, 75 cm
Figure 3: Raw EMG signal for 5 kg, 140 cm
Figure 4: Raw EMG signal for 10kg, 75cm
Figure 5: Raw EMG signal for 10 kg, 140 cm
B. Time-Frequency Representations of EMG
Spectrogram is used in order to get the important
information in EMG signal processing analysis procedures.
The details about the spectrogram is discussed in the paper
[19] and [21]. Figure 6 show the time frequency representation
of spectrogram method in order to display the frequency, time
and amplitude for the EMG signals. Instantaneous RMS
Voltage (Vrms(t)) is extracted from spectrogram the displayed
the performance of the signals. It indicated the four phases
stated in the manual lifting experiments as shown in Figure 7.
Figure 6: Example of spectrogram analysis
Figure 7: Example of Instantaneous RMS Voltage (Vrms(t))
C. Performance Comparison of Manual Lifting Task
Mean is the parameter to tell the strength used of the muscle
for the EMG signal analysis [7]. Mean data are taken from the
mean Instantaneous Root Mean Square (RMS) Voltage
(Vrms(t)). The comparing is divided into four cases which are 5
kg 75 cm, 5 kg 140 cm, 10 kg, 75 cm and 10 kg 140 cm.
Subject 1 is sport man with the 174 cm height and thin,
Subject 2 is sport women with the 169 cm high thin, Subject 3
is sport man with the 166 cm high and fatter, last Subject 4 is
normal tough man 167cm fatter. In this result section, just two
phase is selected to be shown the example pattern of the
subject’s performance.
a. Manual Lifting of 5kg mass of load, 75cm lifting height
Figure 8(a), (b), represent the comparison from two from
four phase which is Phase 1 and Phase 2 to know the
performance of four subjects from ten involved in the manual
lifting tasks. In this tasks, it show that subject 1 and subject 2
more perform with the higher voltage and longer time to
fatigue (no of contractions) compared to subject 3 and 4. It is
increasing of mean (Vrms(t)) which is the strength when the
mass of load and lifting height in bigger.
In comparing this two selected phases, it show Phase 2
(Figure 8(b)) give higher strength compared to Phase 1(Figure
8(a)) because the subject have to lift the load that acquire more
strength compared to located the load at 5 kg and 75 cm.
0 0.5 1 1.5 2 2.5 3 3.5 4
x 105
-1.5
-1
-0.5
0
0.5
1
1.5x 10-3
Sample (N)
Voltage (V)
RAW Signal (5kg, 140cm)
0123456
x 105
-1
-0.5
0
0.5
1x 10-3
Sample (N)
Voltage (V)
RAW Signal (5kg, 75cm)
0 0.5 1 1.5 2 2.5 3 3.5
x 105
-1.5
-1
-0.5
0
0.5
1
1.5x 10-3
Sample (N)
Voltage (V)
RAW Signal (10kg, 75cm)
maximum
minimum
maximum
minimum
maximum
minimum
minimum
maximum
Time (ms)
Frequency (Hz)
Contour TFR
1000 2000 3000 4000 5000 6000 7000 8000 9000
10
20
30
40
50
60
70
80
90
100
1
2
3
4
5
6
7
8
x 10-10
01000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0
1
2
3
4
5
6
7
8x 10-8
Time (ms)
Vrms(t)
Intanteneous RMS Voltage
Phase 1 Phase 2 Phase 3 Phase 4

Journal of Telecommunication, Electronic and Computer Engineering
32 ISSN: 2180-1843 e-ISSN: 2289-8131 Vol. 8 No. 7
(a)
(b)
Figure 8 (a) and (b) The performance of Mean (Vrms(t)) by the Subject 1,
Subject 2, Subject 3 and Subject 4
b. Manual Lifting of 5 kg mass of load, 75 cm lifting
height
The performance of four subjects involved is presented in
Figures 9(a) and (b). It show that Subject 1 and 2 still better
performance with higher strength and longer time to achieve
fatigue muscle. In this task, it is difference performance of
strength higher because at 140 cm lifting height, it acquire
more afford and harder for the subject with the lower high to
arrange the load onto the shelf, but for the taller subjects, it not
give much problem to them with 5 kg mass of load.
(a)
(b)
Figure 9 (a) and (b) The performance of Mean (Vrms(t)) of 5 kg 140 cm by
the Subject 1, Subject 2, Subject 3 and Subject 4
c. Manual Lifting of 10kg mass of load, 75cm lifting
height
Based on Figures 10(a) and (b), the subject’s performance
become different situation compared to the previous results.
From the subjects performances, it show that in heavier mass
of load, Subject 3 and 4 are higher performance compared to
Subject 1 and 2.
In this task, Subject 3 produced the second higher of
strength but longest time to achieve fatigue muscle. Subject 2
with highest strength but less the number of liftings. Subject 1
and 2 almost similar performance. The performance of the
subject almost similar the strength and although still
difference the time to fatigue muscle (number of lifting).
(a)
(b)
Figure 10 (a) and (b): The performance of Mean (Vrms(t)) of 10kg 75cm by
the Subject 1, Subject 2, Subject 3 and Subject 4
d. Manual Lifting of 10kg mass of load, 140cm lifting
height
In this task, it present the Subject 3 have used the highest
strength and longest time to fatigue compared to Subject 4,
Subject 2 and Subject 1. Subject 4 also quit higher strength
have used at the beginning of the manual lifting but drastically
decrease as same like the performance of Subject 1 and 2.
It is the same situation cross to the number of lifting can
produced by the subjects, the higher strength produced while
doing the lifting task the longer time of lifting to achieve
muscle fatigue.
0
0.00005
0.0001
0.00015
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
SUBJECT 1 SUBJECT 2
SUBJECT 3 SUBJECT 4
0
0.00005
0.0001
0.00015
0.0002
0.00025
0.0003
0.00035
1357911 13 15 17 19 21 23 25 27 29 31 33 35
SUBJECT 1 SUBJECT 2
SUBJECT 3 SUBJECT 4
0
0.0001
0.0002
0.0003
0.0004
0.0005
1 2 3 4 5 6 7 8 9 1011 12 13 14 15 16 17 18 19 20 21 22 23 24
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
0
0.00005
0.0001
0.00015
1234567891011 12 13 14 15 16 17 18 19 20 21 22 23 24
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
0
0.0001
0.0002
0.0003
0.0004
0.0005
12345678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
1357911 13 15 17 19 21 23 25
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
Vrms
No. of lifting
No. of lifting
Vrms
No. of lifting
No. of lifting
Vrms
Vrms
No. of lifting
No. of lifting
Vrms
Vrms

Performances Comparison of EMG Signal Analysis for Manual Lifting using Spectrogram
ISSN: 2180-1843 e-ISSN: 2289-8131 Vol. 8 No. 7 33
(a)
(b)
Figure 11(a) and (b) The performance of Mean (Vrms(t)) of 10kg 140cm by
the Subject 1, Subject 2, Subject 3 and Subject
The comparison of all the performances for manual lifting
tasks is presented in Appendix A. Four subjects have selected
to be shown in the analysis process. The difference of task will
produce the different number of liftings. Each task is divided
into four phases as stated. Each will have the starting (1st
lifting) and ending (the end of lifting) mean Vrms(t) voltage
(strength). Either all phase, it would be focus on the highest
strength Phase 2 and Phase 3 which while travel the load and
arrange the load onto the shelf. All the subjects show by
increasing the mass of load and lifting height, the number of
lifting that would able to handle decreased but the strength
increase. At this phase it required more strength to handle the
load. V. CONCLUSION
Based on the analysis of EMG signals, this study concluded
that the application of spectrogram is able give the information
of the subject’s performance based on the variable lifting
height and mass of load from the determining of time-
frequency representation (TFR). From the summary of
Appendix A, it clearly show the relationship of the parameter
and physical condition of the subjects. All of this factors
would be affect the strength and time to fatigue. Subject 1 and
Subject 2 have the advantage to the higher lifting height, but
disadvantage to the higher mass of load. Furthermore, the
mean instantaneous RMS voltage (Vrms) which is strength
increased when the lifting height and mass of load is
increased. However, number of lifting would affected by the
strength produced by the subjects.
ACKNOWLEDGMENT
The authors wish to thank Universiti Teknologi Malaysia
(UTM) and Ministry of Higher Education Malaysia for
providing the funding and facilities to conduct this research
with Project No 05H51.
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0
0.0005
0.001
0.0015
0.002
12345678910 11 12 13 14 15 16 17 18
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
0
0.00005
0.0001
0.00015
0.0002
0.00025
12345678910 11 12 13 14 15 16 17 18
SUBJECT 1 SUBJECT 2 SUBJECT 3 SUBJECT 4
No. of lifting
No. of lifting
Vrms
Vrms

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APPENDIX
Appendix A shows the comparison of the performance of manual lifting tasks.
Parameters
Number of
liftings
Mean of (Vrms(t))
Phase 1
Phase 2
Phase 3
Phase 4
Start
End
Start
End
Start
End
Start
End
Subject 1
5 kg 75 cm
36
95.7
13.6
301.4
75.6
273.8
85.7
106.4
29.5
5 kg 140 cm
23
49.2
13.9
290.1
79.1
394.5
243.5
136.6
63.9
10 kg 75 cm
21
186.0
17.3
309.0
100.2
400.0
151.2
184.3
43.9
10 kg 140 cm
13
66.1
26.7
323.9
135.8
491.7
337.1
165.2
19.6
Subject 2
5 kg 75 cm
36
110.1
11.8
272.9
55.3
226.2
99.5
103.5
30.8
5 kg 140 cm
24
83.6
13.2
313.7
37.0
333.0
196.7
136.2
50.5
10 kg 75 cm
21
61.0
17.1
298.0
110.0
348.2
187.1
134.4
29.5
10 kg 140 cm
12
85.3
32.0
326.5
165.9
530.7
223.5
130.8
30.9
Subject 3
5 kg 75 cm
25
86.9
13.0
194.0
86.0
238.3
26.0
86.9
13.0
5 kg 140 cm
18
178.5
20.3
302.2
15.0
151.5
73.9
113.9
15.2
10 kg 75 cm
25
296.0
14.4
479.1
254.4
628.3
298.4
104.4
27.8
10 kg 140 cm
18
448.3
61.9
1183.3
619.2
1422.4
793.3
146.2
54.8
Subject 4
5 kg 75 cm
27
96.3
12.0
162.9
32.2
203.0
32.0
88.2
13.0
5 kg 140 cm
19
138.0
15.4
248.8
46.2
203.0
71.7
121.0
16.5
10 kg 75 cm
25
448.3
61.9
1183.3
619.2
1422.4
793.3
146.2
54.8
10 kg 140 cm
17
295.3
15.4
971.8
175.6
1280.8
125.9
207.7
29.6