A Radial-Ulnar Deviation and Wrist-Finger Flexion Analysis Based on Electromyography Tanzim Kawnine A Bachelore of Science Thesis in Electronics Mälardalen University, Sweden Department of Computer Science and Electronics 2008 Supervisor & Examinator: Baran Cürüklü 1
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A Radial-Ulnar Deviation and Wrist-Finger Flexion Analysis Based on Electromyography
Tanzim Kawnine
A Bachelore of Science Thesis in Electronics Mälardalen University, Sweden
Department of Computer Science and Electronics 2008
Supervisor & Examinator: Baran Cürüklü
1
Abstract
This study is aimed to determine the electromyographic signals of the forearm, using Ag/AgCl electrodes. The four major muscles of forearm, which are providing the bioelectrical currents, have been displayed and analysed to determine the different activities. In order to record the signals, an EMG device has been developed and installed and a schematic has also been presented in this paper.
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Chapter 1: Introduction
EMG, it is a nerve conducting test, performed by measuring the bioelectric signals from
the muscle of a human body. Muscular movements cause the action of muscles and nerves,
which provide electrical currents. These currents are generated by the interchange of ions
across the muscles which make a part of the signalling process for the muscle fibres to
contract. It can be measured by applying conductive elements or electrodes to the skin
surface, or invasively within the muscle. It is non-invasive and can be conducted very easily
with minimal risk to the subject.
The main object of this thesis is to design and develop hardware for measuring EMG
signals from real human muscles of forearm. The provided signal will help us to understand
the different movements of the muscles of forearm.
Measurement of surface EMG is dependent on the amplitude of the surface EMG signal.
The signal varies from μV to mV range. Since the signal level is to low to capture on the
display, it is required to amplify the signal level to a TTL level (between -5 volts to +5 volts).
Many critical factors should be considered before the signal is displayed properly, such as the
electrical signals are distorted by noises and artefacts. Additional DC current could also
provide offset to the EMG signal. Without a proper ground reference, the signal could be
misleading. Finally yet importantly, the size of the device should be considered.
The basic hand muscle activity is located in forearm. The four muscle groups are 1) the
extensor carpi radialis 2) the extensor communis digitorun 3) the extensor carpi uilnaris and
4) Flexor carpi radialis. The EMG device which has been developed for this project has only
one channel. By attaching two electrodes from each muscle group to the device, the EMG
signal has been analysed, when the muscle contraction and various hand movements were
made.
Chapter 2 provides descriptions of upper mentioned muscle groups and their location
within the forearm.
5
In chapter 3, the physiology of EMG has been discussed. It contains brief information
about the nervous system and muscle tissue applications and also about the action potential of
the muscles.
Chapter 4 provides a detail of implementation of the EMG device with a basic
description of preamplifier, filtration and additional amplifier with bias adjustment. Each of
the components is described through circuit diagrams and key equations.
Chapter 5 discusses the result of the movements of different muscles groups of forearm.
The experiment consisted of radial and ulnar deviation and also wrist and finger flexion and
extension of the hand. The various signal patterns of the muscles has been illustrated in this
chapter.
Finally, chapter 6 provides the summary of the thesis and discusses the future work.
6
Chapter 2: The Forearm Muscles
The forearm is a structure on the upper limb. The forearm consists of two bones, the
radius and ulna. It contains many muscles such as the extensor carpi radialis, extensor
digitorum comunis, extensor carpi ulnaris, Flexor carpi radialis and a few more. These muscle
are chosen to be described in this chapter because of their contraction and relaxation states
have been measured and analysed by this EMG measuring device.
2.1 Extensor carpi radialis
The extensor carpi radialis is located beneath the Brachioradialis (see figure 2.1). It is
one of the main muscles that control the movement of the wrist. It starts at the lateral side of
the humerus and it is inserted into the dorsal surface of the base of the second metacarpal
bone [11]. The muscle is an extensor at the wrist joint. It manipulates the wrist to move the
hand toward the thumb and away from the palm.
2.2 Extensor digitorum communis
The Extensor digitorum communis arises from the lateral epicondyle of the humerus, by
the common tendon; from the intermuscular septa between it and the adjacent muscles, and
from the antibrachial fascia [11]. The Extensor digitorum communis extends the phalanges,
then the wrist, and finally the elbow. It tends to separate the fingers as it extends them [C].
Figure 2.2: Extensor digitorum communis visible in blue at center. http://upload.wikimedia.org/wikipedia/commons/5/5f/Gray418.png
Figure 2.1: Superficial muscles of the forearm. Extensor carpi radialis longus visible in blue. http://upload.wikimedia.org/wikipedia/commons/0/07/ECR-longus.png
2.3 Extensor carpi ulnaris
The Extensor carpi ulnaris is located on the ulnar side of the forearm (see figure 2.3
below). It originates from the lateral epicondyle of the humerus, and is inserted into the
prominent tubercle on the ulnar side of the base of the fifth metacarpal bone [11]. The
Extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the
ulnar side; by its continued action it extends the elbow-joint [D].
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Figure 2.3: Extensor carpi ulnarisvisible in yellow at centre right. http://upload.wikimedia.org/wikipedia/commons/5/5f/Gray418.png.
Figure 2.4: Flexor carpi radialis visible in blue in the centre of forearm. http://upload.wikimedia.org/wikipedia/commons/5/59/Flexor-carpi-radialis.png
2.4 Flexor carpi radialis
Flexor carpi radialis (see figure 2.4) is another muscle of the forearm that acts to flex of
the hand. The muscle arises from the medial epicondyle of the humerus and inserts into the
palmer surface of the base of the second metacarpal [11].
8
Chapter 3: Physiology of EMG
EMG stands for electromyography, also referred to as myoelectric activity and
measuring the electrical impulses of muscles at rest and during contraction. Muscle tissues
conduct electrical potential similar to the way nerves do and these electrical impulses are
called action potentials. The information present in the muscle action potential can be
recorded by applying the surface EMG method. It is important to consider two main issues
when the detection and recording of EMG signals occur. The first is the signal-to-noise ratio.
It is the ratio of energy in the EMG signals to the energy in the noise signal. Noise is
something that is not desired in a pure EMG signal. The second one is the distortion of the
signal.
The EMG signal is picked up by electrode and amplified. It usually needs thousand
times of amplification before it could be shown on a display and can be recorded. By
amplifying the input signal, the noise signals are also amplified from the skin and other
factors that may affect the outcome signals. The point of interest of the signal is the
amplitude, which has a range between 0 to 20 millivolts (peak to peak). The frequency of an
EMG signal is between 0 to 500 Hz. However, the usable energy of EMG signal is between
50 to 150 Hz.
Many dependent factors could affect surface EMG. Electrical noise can be categorised
into the following types:
1. Inherent noise in electronic equipments: All electronics equipments cause noise. It is
next to impossible to eliminate the perturbed signals but by applying proper filter, the
noise can be reduced to minimum.
2. Ambient noise: Electromagnetic radiation is the source of ambient noise. Ambient
noise level is the background noise level, reference sound level or room noise level.
“It has amplitude that is one to three orders of magnitude greater than the EMG signal
[6]”.
3. Motion artefacts: Two main sources give rise to motion artefacts, namely electrode
interface and electrode cable. A proper design of the circuitry and shield wires will
reduce the noise.
9
The following steps can do the maximisation of the quality of EMG signal:
1. The signal to ratio should consist of the highest amount of data from EMG signal and
as minimum amount of noise as possible.
2. The distortion of EMG signal should be as minimum as possible with no unnecessary
filtering.
3.1 The Nervous System and Muscle Tissues
The brain, the spinal cord and peripheral
nerves are the three main parts of the nervous
system. It controls the communication system of
the body. There are two main types of tissues in
our nervous system: excitable tissue and non-
excitable tissue. The excitable cells are called
neurones, which communicate with different
parts of the body, responding to and
transmitting messages in the form of nerve
impulses from one part of the body to another. Figure 3.1: Skeletal muscle structure http://www.octc.kctcs.edu/gcaplan/anat/images/
Image285.gif Non-excitable tissues do not response to voltage
or any other conventional stimulus.
Excitable tissues can be classified into four components, namely sensory receptors,
neurone cells bodies, axons and muscle fibres. A contact with a hot surface will cause pain
and pressure which will be transmitted by sensory receptors. The neurone sends the message
along a nerve axon (also called nerve fibres) to the spinal cord. There are two types of axons:
the afferent axon and efferent axon. The afferent axon also called as sensory axon, transmits
the signals to the nervous system and carries information from sensory receptor to the spinal
cord or brain. The efferent axon (motor axon) originates at the spinal cord transmits the
information through the body parts.
A muscle consists of specialised cells capable of contraction and relaxation. These cells
generate forces, help us to move and give us the ability to communicate and make
expressions. The four main functions of the muscle tissues are: producing motion, moving
substances within the body, providing stabilisation and generating heat. The tissues also can
10
be identified based on structure, contractile properties and control mechanism: (i) skeletal
muscles (ii) smooth muscle (iii) cardiac muscles. The EMG is applied to the study of skeletal
muscle.
As it is shown on figure 3.1, that skeletal muscles are attached to the bone and the
muscle contraction of skeletal muscles are responsible for movement of the skeleton. The
muscle contraction initiates by impulses in the neurones to the muscle. These neurones are
called as “motor neurone”. One motor neurone usually supplies stimulation to many muscle
fibres.
3.2 Action Potential
Each nerve impulse triggers an electrical
discharge, or action potential, in each of the
muscle fibres that it stimulates. Under normal
condition, Na+ and Ca+ are more concentrated
in the extra cellular fluid and K+ is more
concentrated with in the cell. Na+ generates
the electrical signals. When a cell goes from
resting to an excited state, it increases its Na+
permeability. Then the Na+ molecules enter
the cell through voltage-gated channels. The Figure 3.2: Action potential model
http://static.howstuffworks.com/gif/nerve-12.gif
extra positive charge of Na+ to the intracellular fluid causes the cell to become depolarised
and initiate an action potential. The action potential starts at the point of innervations and
spread along the muscle fibres toward the two ends of the fibre. These AP’s activate the
contractile apparatus inside the muscle fibres. It also produces an electrical potential in the
surrounding muscle tissue, which can be detected by a needle or fine-wire electrode.
As it was mentioned earlier, the nervous system controls a muscular contraction by
turning motor units on and off and by controlling their discharge rates. When a motor unit
discharges, the electrical potentials from all the muscle fibres of the motor unit sum together
to produce a compound potential called the Motor Unit Action Potential (MUAP). This is a
matter of one to several milliseconds. The electrodes play an important role here because the
exact size and shape of MUAP depends on where the electrodes are placed on the skin.
11
MUAPs differ from one motor unit from another with different shapes, but by the same
electrode from the same motor unit have more or less the same shape.
An EMG signal is the train of Motor Unit Action Potential (MUAP). The signal contains
the muscle response to neural stimulation. It appears randomly in nature and is modelled as a
filtered impulse process. “The MUAP is the filter and the impulse process stands for the
neurone pulses” [6].
3.3 Amplifier and EMG Signals
An EMG amplifier amplifies the signals generated by the muscles. It boosts the low
power signal to high power signal, so the signal is usable to perform work. The amplification
increases the signal level and protects an electrical interference during transmission. The
amplified signal can also be stored in a device or displayed on a oscilloscope.
A differential amplifier has the ability to eliminate the noise from the EMG signal.
Figure 3.3 shows the diff-amp with two inputs, which are subtracted, and the signal
difference is amplified and become the output signal.
Figure 3.3: A schematic of the differential amplifier configuration http://p3.smpp.northwestern.edu/BMEC66/weightlifting/images/armelectrode.jpg
A perfect subtraction is next to impossible. Therefore, a Common Mode Rejection Ratio
(CMRR) is applied to measure the accuracy of subtraction in each amplifier. If the CMRR
value is at 90 dB, it could discard the noise. However, most of the amplifiers nowadays could
make a CMRR value of 120 dB. All though, there are some noises that still could exist. The
12
noise could be injected into the signal by a stray capacitance and then the signal is amplified.
As a result, a degrading signal can be seen on the display.
An amplifier itself is an effective filter. The electrode itself usually has lower impedance
in a case of higher frequencies and has higher impedance for lower frequencies. The
electrodes, cables and amplifier create an implicit filter effect. This filter could cause errors in
the signal if it is not designed carefully. To reduce an implicit capacitance effect, the
electrodes should be placed near the amplifier, which means the amplifier should be located
as close to the signal source as possible.
13
Chapter 4: Method and Materials
The EMG machine is designed to measure and record signal from human nerves and
muscles. A part of the machine known as differential amplifier compares the electrical
activity at one point to a reference point, which is considered zero. This will determine the
difference between the active point and the reference point and shows the difference on the
display of the oscilloscope for interpretation.
The amplifier is set to display various levels of gain. The sensitivity of the amplifier
increases or decreases the size of the waveforms of the forearm on the display. The increasing
sensitivity can cause an increase in level of noise and artefacts which make the small
electrical potentials very difficult to identify. Filters could be applied to minimise the
background noise and artefacts, enhancing the electrical potential to be seen on the screen.
Bio-electric signal in Pre-amplifier Notch-filter
Amplified signal out
Bias Adjustment
Additional Gain
Figure 4.1: A simple block-diagram of EMG device
4.1 Preamplifier and Body Reference Circuit
To build an EMG device, an instrumentation amplifier is needed. A BURR-BROWN
INA2128 chip is used for the preamplifier and OPA2604 for the body reference circuit and an
OPA2277 for the notch filter. The preamplifier is a type of a differential amplifier. The data
sheet of INA2128, OPA2604 and OPA2277 is shown in Bibliography.
This figure 4.2 shows a preamplifier circuit and the body reference circuit from only
one channel.
14
Figure 4.2: Preamplifier with body reference circuit
The equation for gain is [5]:
G
501R
kGain +=
R1 = R2 = 22 ohm and RG = 22 x 2 = 44 ohm, and the gain is approximately 1137 times. It is
sufficient for the amplification of our EMG signals. The body reference circuit that is
connected to the preamplifier acts as a ground. The details of the circuit will be discussed
later.
4.2 Gain and Bias Adjustment
This section is considered as the second stage of the EMG amplifier. The amplifier and
the bias adjustment help us with an ability to adjust or correct the output signals in different
circumstances. For instance, if the bioelectric signals of the forearm do not have enough
amplitude after the pre-amplification stage or if the signal is not high enough for an A/D
converter or perhaps the signal still has a bias or offset. These problems could be resolved by
applying the gain and bias adjustment.
The EMG machine has only one channel and it has an individual gain adjustment unit
and an individual bias adjustment unit. These units are applied after the signals passed
through the pre-amp stage and the filtering stage, where the noises and artefacts are reduced
to minimum level.
15
This EMG device has a limitation of the gain and the bias adjustment. It can be
amplified about 21 times. The bias adjustment adjusts the signal up or down by the level of ±9
volts. In the nature of op-amp, the output cannot be more or less than the power supply
voltage. For instance, the amplifier is fed with one volt, which has a gain equal to four, and
the offset has increased by positive 2 volts, the output of the op-amp would be 6 volts. This is
acceptable because the output voltage is still within the voltage range. However, if the input
level is the same but the gain of the op-amp has changed from four to eight times with the
same offset level, the calculated output would be 10 volts because of the characteristics of the
op-amp.
The amplifier in the device uses basic non-inverting amplifier circuit. The gain could be
adjusted by using a potentiometer, which is parallel to 10k (R2), shown on the next page (see
figure 4.5).
4.2.1 Amplifier (the additional gain)
Figure 4.5: Amplifier circuit with gain adjustment
The gain can be computed by:
)1(
)1(
13
14
13
14
RRGain
VV
RRVV
in
out
inout
+==
+=
This non-inverting amplifier circuit is built by using OPA2277 chip, a dual op-amp. The
purpose of using an OPA2277 is to use the inputs for the gain and the bias adjustment circuit,
making the whole circuit looks more compact.
16
The compensation resistor R12 is placed to reduce the error in the output voltage, which
is equal to the parallel combination of R14 and R13. R14, the potentiometer is used to
increase or decrease the additional gain. When R14 is adjusted to 0, there is no additional gain
(gain = 1). On the other hand, the R14 is adjusted to the maximum of 200k; the gain is equal
to 21 times.
4.2.2 Bias Adjustment
Figure 4.6: Bias adjustment circuit
Bias adjustment circuit increases or decreases the reference level of the signal.
Reference level of a signal is at ground line or zero volts. If it is not at the ground line, or if
the reference level needs to be changed, the bias adjustment enables us to adjust the reference
level or the desired level.
The ground level is created by using a potentiometer. The change of the potentiometer
affects the reference level to the output voltage. To adjust the reference level at the output
voltage, the calculations of three different cases are needed. When the potentiometer R9 is
adjusted to 0%, 50% and 100%, Vout is equal to:
adjinout VGainVV ±×= )(
Where, V1 < Vadj < V2. V1 = +Vcc and V2 = -Vcc.
Therefore 0%, 50% and 100% are the values of +Vcc, ground level or zero and -Vcc
respectively.
Using the equation from the previous page, the output of the circuit can be computed as
follows:
17
• At 0% of R9: (R9= 0 ohm, Vadj = +Vcc volts)
)1(8
10
RRGain +=
ccinout VRRVV ++= )1(
8
10
• At 50% of R9 (R9 = R9/2 ohms, Vadj = 0 volts)
)
2
1(9
8
10
RR
RGain+
+=
)
2
1(9
8
10
RR
RVV inout
++=
• At 100% of R6: (R6 = R6 ohms, Vadj = -Vcc volts)
)1(98
10
RRR
Gain+
+=
ccinout VRR
RVV −+
+= )1(98
10
The output of the circuit from the second equation is referenced by a virtual ground
level. While on the first and the third equation, the additional voltages were added to the
output level either positive or negative. By using this concept, the offset of the output voltage
can be adjusted.
In this EMG device, an OPA2277 chip is used for one channel. OPA2277 has ultra low
offset 10µV, high open-loop gain (134 dB), high CMRR with four inputs, which is an
outstanding chip for the whole gain and bias circuit system [4].
18
U1A
INA2128UA
2
1
89
6
5
3
4
7
C210pF
J1
PhonePlug2
2
1
3 R122Ω
R222Ω
U2A
OPA2604AP
3
2
4
8
1U2B
OPA2604AP
5
6
4
8
7
R3
10kΩ
R4
390kΩ
R5
390kΩ
VCC9V C3 100nF
C4
100nF
C5 10nF
R691kΩ
VEE-9V
VEE -9V
VCC9V
VCC
9V
VEE-9V
Figure 4.7: The preamplifier with the filter and a body reference circuit
Figure 4.8: The gain adjustment circuit
Figure 4.9: The bias adjustment circuit
19
Chapter 5: Result
This chapter presents recorded samples of EMG
signals of forearm muscles. The signals were recorded from