Muscle Activation and Movement Coordination: EMG Analysis

This report delves into the intricate relationship between muscle activation and movement coordination, employing electromyography (EMG) as a primary tool for analysis. It begins with an introduction to muscle anatomy, focusing on key muscle groups like the quadriceps femoris, hamstring muscles, gastrocnemius, and tibialis anterior, highlighting their roles in various movements and the impact of the anterior cruciate ligament (ACL) on joint stability. The report then provides a detailed overview of EMG, including the methods used to analyze the signals. These methods include baseline shifting, signal filtering, smoothing, and amplitude normalization. The experimental procedure, including EMG testing, is outlined to illustrate how these techniques are applied to study muscle function. The report examines how EMG data can provide insights into muscle coordination during different activities and how injuries, such as ACL damage, can alter muscle activation patterns. This analysis helps in understanding the biomechanics of human movement and the effects of injuries on the musculoskeletal system.

MUSCLE ACTIVATION
AND MOVEMENT
COORDINATION

Table of Contents
INTRODUCTION...........................................................................................................................1
2.1.2 Anatomy of Muscles......................................................................................................1
2.2 Electromyography............................................................................................................4
2.2.1 Shift in base line...........................................................................................................1
2.2.2 Filtering of signal..........................................................................................................1
Formula 1 (Page12)................................................................................................................1
2.2.3 Smoothing of signal.......................................................................................................2
Formula 2................................................................................................................................2
2.2.4 Normalisation of Amplitude..........................................................................................2
Method 3.........................................................................................................................................3
3.3 Experimental procedure....................................................................................................4
3.3.1EMG testing....................................................................................................................4

INTRODUCTION
Human muscles react during various sequences and events when they get injured this can
be identified with the method of using Electromyography which provides information about how
the muscles will coordinate in such situations.
2.1.2 Anatomy of Muscles
The muscle redundancy would be very complicated to investigate in scientific study
about how human muscle coordinates in each action or motion. Generally, the large muscle
group is focused. The project determined the motion performed by the few of the involved
muscles which is mainly performed by lower extremities will be examined. Preferably, muscle
motion is the topic of the study.
Quadriceps femoris at the front side of thigh is the four muscle group. Group of these
four muscles which extends to the knee joint and contracting concentric. Quadriceps femoris is
consist of muscle on femur and Vastus intermediate which forms the middle portion of thigh
muscle group, at the sidelong Vastus Lateralis and at the central side the Vastus medialis (Hamill
& Knutzen, 2009). The position of muscle attachment is being different, as the separate actions
can be done by each muscles which has additive functions. Figure 2.2 is presenting the sites of
Quadriceps leg-bone muscles joints.
Figure 2.2. Right quadriceps Femoris muscles. in (A) the Quadriceps femur is presented in
a armoured off view, (B) Represents the muscle group.
The Rectus femoris is the only attachment for two acting muscles of Quadriceps femur.
The pelvic bone is joint with it instead of thigh bone, this both acts as the knee and hip skeleton
muscle. The rectus femoris functioning is depends upon lever with respect to different
conjunctions. The ability of femur muscles will be extend to the knee conjunction become
limited, if the hip attachment is flexure, apart from its ability differs the hip joint is been
facilitated. Reciprocally, rectus femoris acts favourably as knee extensor if hip is strained
(Hamill & Knutzen, 2009).
The right side of thigh muscles is the strongest and and largest Quadriceps femoris. The
attachment of vastus lateralis the position and joint of thigh bone to patella implement the
outermost power to knee junction. The contribution in the correct positioning of Patella is done
with the help of left muscle and the central contractive organ of the thigh (Hamill & Knutzen,
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2009). The Intermedius vastus cannot be examined by Electromyographic researches due to its
deep positioning behind the rectus leg-bone.
The knee flexion is by the help of hamstring muscle group. It is positioned at the back of
thigh and including the Semi-tendinosus, the Semi-membranosus and the biceps leg bone
muscles (Hamill & Knutzen, 2009). The location of hamstring muscle is presented in the Figure
2.3. These all three muscles of hamstring are conjucted to the Ischial tuberosity, which is
prominent bony at the lower side of pelvic bone, it effects the muscle to react upon two
attachments. Apart from the functioning of knee the hamstring muscle forces ischial tuberosity
lower side when the muscles bidding, which results the hip flexor (Hamill & Knutzen, 2009).
As per the fact the hamstring includes the bilateral attachments of muscles, which
complexed the contractive organ's functioning. The knee and hip flexor implements the rising
motion from a squatting locations. The quadriceps femoris do efforts to extend the knees would
be countered by the hip skeleton muscle which is contributed by tendon muscle's contraction.
Moreover, the torment muscle act's more effectively as knee extend with the position of hip
flexion (Hamill & Knutzen, 2009).
Figure 2.3. Right tendon muscle. The armoured off view of the three muscles in (A), and
the context showed them in (B).
In the hamstring group the most outer side position is of the biceps femoris. The
contraction of these muscle affects, earlier determined functions, extraneous lower leg rotation.
The central part of tendon muscle is consists of Semi-tendinosus and Semi-membranosus, and
the movement of lower leg internally with its response (Hamill & Knutzen, 2009). The three
muscles and their joints are exposed and shown separately in Figure 2.4.
Figure 2.4. Right hamstring's three muscles and their conjunction visible fully.
The semi-membranosus is positioned deep in side the thigh, which is somehow beneath
the semi-tendinosus, the semi-membranosus and semi-tendinosus are very adjacent together.
Therefore, it is difficult to differentiate these two muscles while recordings muscle functioning
with the help of Electromyographic.
Pushing the toes downward is the function of flex-or which is in terms of plantar flexion.
The primary movers of this action is gastrocnemius, which is a muscle positioned at the back of
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lower leg. This attached to the lower end of the femur and which is a two- joint muscle and is
able to flexible the knee. As per the mechanical point of view this is much effective as the
plantar flaxor while the knee attachment is extended (Hamill & Knutzen, 2009). the medial ad
the lateral head are two sections divided by this action as per belly muscle. The gastrocnemius
anatomy is illustrate in figure 2.5. The gastrocnemius is necessary for the muscle action which is
example for the Plantar flexed is required for standing on feet.
Figure 2.5. Plantar flexion is the contribution of the primary muscles.
The opposite action of plantar flexion is Dorsiflexion. The toe moved distal to the tibia
and when the dorsiflexed of foot is tilted up. (shin bone, in Figure 2.6). The most powerful and
the primary dorsi-extentor is positioned in the front and lateral side of tibia is the tibialis anterior
(Hamill & Knutzen, 2009). this frontal skeleton muscle and its location is presented in Figure
2.6.
Figure 2.6. Dorsiflexion of muscle contribution.
2.1.3 Anterior Cruciate Ligament
The connective tissue which binds bones is a short band of tough fibrous called as a
ligament. The support in one direction is usually awarded by the ligaments. Cause they controls,
stabilize, and limits the attachment motions, which influences the joint movement in sever
injuries. Injuries to ligament can affect the conjunctive instability, which cause the alteration in
joint kinematics and results in emended the load distribution (Hamill & Knutzen, 2009).
the intra-articular ligament is classified by the anterior cruciate ligament, which means
the it is positioned beneath the attachment it supports. The downward end of the femur to the
upper most site of tibia are connected to one of its ligaments. The ACL position is shown in
Figure 2.7. ACL protects the tibia from moving progressive relative to the thigh bone is one of
its primary function. In addition to this context, ACL limits the outer most movement of the knee
joint (Immersion Media, 2011).
Figure 2.7. Beneath the patella bone (knee cap) the anterior cruciate ligament can be seen.
The planar and rotator instability can be created if an injury of damage occurred to ACL,
when ACL function is diminished while stabilizing. The other structures got damaged is
depending upon the variety of directions occurred due to rotator instabilities, when the upward
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movement of tibia which is usually from instability planar. The stress on the secondary
stabilizers of the knee is added by the instabilities created when an inefficient or missing ACL
locations (Hamill & Knutzen, 2009).
Compration of the tendon muscles use the traction force upon the tibia and puts it back
side, which is decreasing the stress inside the ACL, irrespective to the degree of knee extension
(Lass, Kaalund, leFevre, Arendt-Nielsen, Sinkjaer, & Simonsen, 1991).
The primary studies of electromyography of muscle coordination while the gait in front
of subjects with a complete injury of the ACL, at the period of activation of contractive organ's
movement functioning on the knee attachment is been rectified by the systematic deviation
(Lass, Kaalund, leFevre, Arendt-Nielsen, Sinkjaer, & Simonsen, 1991). Generally, muscles
functioned when the injured knee priorly when the heel connects to ground, and the time of
muscle activity is drawn out (Lass, Kaalund, leFevre, Arendt-Nielsen, Sinkjaer, & Simonsen,
1991).
2.2 Electromyography
In abbreviation, while implementing the use of electromyography, the electrodes were
used to observe the signals from human's neural systems to the muscles. There were two various
kinds of electromyography, above ground and intramuscular EMG, the variations between them
is in nature of electrodes used in it. Electrodes are located at the on the human skin while using
the EMG of surface. The muscles of interest were perforated with electrodes in the form of
needles while using intramuscular EMG.
Needle techniques can torn muscle tissues and effect sever pain during the action, the
abnormal lead of the movement or action pattern. From its aggressive nature, the medical
personnel is also required by the needle techniques. With the needle electrodes, the magnitude of
muscles from the signals can be taped is comparatively small, and it might not be represents the
total muscle volume involved (Hug, 2011). Accordingly, the main focus is on the surface EMG
by this section.
The methods of processing EMG details for the cause of providing analysis about EMG data
which is already exist. The primary research and work in accordance to provide the direction to
this project is examined in this section.
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2.2.1 Shift in base line
The measured neural signal which passes from the two electrodes and the potential difference
which occurs from the Outcome can either be positive or negative. As a result, The mean value
of the raw EMG will we zero because the data points of the outcome will occur in pair with
reverse signs. It can be said that the baseline should be at zero of the Graph of the neural signal
of EMG (Konrad 2006). The presence of constant systematic interference is indicated by an
offset of the baseline. The baseline should be centred at zero to resolve the problem after
removing the offset.
The shift in the baseline is visible in the graph shown below:
2.2.2 Filtering of signal
The EMG electrodes which ranges 6Hz to 500Hz will help in measuring the frequency of
the neural signals and shows the most power signals between 20Hz and 150Hz and the frequency
interval will also appear in the recorded data (Konrad, 2006). Thus, there are multiple
superimposed frequencies are available in the raw data of EMG and some frequencies are outside
the interval of interest.
Therefore, the result of interference are the frequencies will not origin from the muscles as they
are outside the interval. The Data points of EMG should be filtered to solve the problems.
Recommendations are give for the removal of any output which is outside the interval of
frequency between 10Hz and 500HZ by using the digital band pass filters (Konrad, 2006).
Formula 1 (Page12)
It is a combination of both high pass and low pass filters. The signals of frequencies will be
removed if the high pass filter is used in the digital band pass filter which will be below is below
the cut off frequency of filters. Only enough frequency will pass if the low pass filter is used in
digital band pass filter. An interval or a brand of allowed frequencies is created by the
combination of both the filters which is called a band pass filter.
The Nyquist frequency theorem states that if the signal of frequencies are above the
frequency of Nyquist then the sampling of frequency cannot be done properly and it will result in
aliasing the effect. In order to avoid the loss of information the minimum frequency of 1000Hz is
required for EMG recordings (Stegeman & Hermens, 1998).

2.2.3 Smoothing of signal
The fact has determined that the actual set of motor units which are recruited changes
constantly within the diameter of available motor units with the interference of EMG which is
mainly of random nature and the signals of the motor units will superpose. In addition to this,
The electrodes are attached to the skin not with the muscles when the surface of EMG graph is
used. The position of the electrodes will change through dynamic action relative to the muscle
belly. The result of this outcome is a fact that the reproduction of raw EMG in its possible in the
second time. Minimizing the part of the signal which is non reproducible by applying the digital
smoothing algorithms which will outline the mean trend of development of signal. By using this
the data is transformed in a pattern by removing the steep spikes' data. Several spikes and
irregularities are visible in the raw data of EMG which is shown in the figure 2.10
For the smoothing an algorithm root mean square is established. RMS is a combination of the
value of RMS and a method which can either sliding average or moving average method. All
data point is replaced by the mean value of itself and its neighbouring when the moving average
method is applied. The data which is related with the time serious is determined by the time
window which defined by the user. For example the data point obtained at the time t= 75ms
would be replaced by the mean value of every data point in the interval 50ms <t ≤100ms if the
time window is 50ms. To show the difference between the both RMV value is used instead of
mean value. It is a preferred recommendation for smoothing recommendation for smoothing as it
reflects the mean power of the signal (Konrad, 2006). For the set of discrete values {xi}i=1 N, the
root mean square is defined as
Formula 2
It can be defined by using the time window between 50ms and 100ms, depending on the speed
of movement which is measured. For the fast movement of signal the lower time window is used
and for the slower movements it may be superfluous.
2.2.4 Normalisation of Amplitude
The analysis of EMG is defined that the conditions which are detected will strongly affect
the amplitude of the signals which is a major problem. It can be defined as the general amplitude
which is registered can vary greatly between the sites of electrodes, subjects which are different
even the same muscle site measures. By normalizing the data of signal to the maximum
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voluntary contraction of the subject to a value of reference this problem will be resolved
(Konrad, 2006).
It has been considered that the MVC is tested against the resistance which is static. For a
maximum contraction to be possible the excellent stabilisation and the support of all segments of
body which is involved. To reach the maximum capacity of muscles the subjects which are
untrained may face problems other than the good testing conditions (Konrad, 2006). The
measurement of MVC may get invalid or prevents directly when there is a injury on the body
structure.
There are important benefits which are provided by normalization of MVC. An approximation of
the neuromuscular effort is provided by the normalised data of MVC for a given task. It will
provide a complete understanding about the muscles are working at what capacity level if the
previous method is carried out properly. Secondly, It eliminates the any varying influence of
local conditions of detection of signals by the standard to percent of unique value of reference
(Konrad, 2006).
The clarity of the data which is normalised is highly dependent on the quality of trial on MVC.
The capacity of the muscles varies with its length it is problematic whether for a dynamic
movement a trial can be representative. It is difficult to find a static position where the subject
can contract with the upper limit capacity of its muscles. During the dynamic exercises several
studies have observed readings exceeding MVC (Konrad,2006)
Method 3
3.1 Approach
Research was performed to accomplish the goals in three steps in section 1.1. The first step of
the research has analysed the electromyographic recordings of activation of muscles during the
specific motions were accumulated in the laboratory. The second step will determine that the
data points of EMG was processed by using the software Mathworks Matlab. Several methods
are applied for the filtering, normalizing and smoothing of the recorded activity of the data points
and they are turned graphs are readable. The third step of the activity will determine data of
EMG for the activation of muscles and the contribution of the muscles which are distinct during
the duration of the motions are verified.
3.2 Experimental setup
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A maximum capacity of ten channels used in the EMG apparatus allowed detection of muscle
activation in ten muscle at single time. Along with EMG an installation of two video cameras
was done to record the motions performed. A universal time scale was obtained by the time
synchronisation of two video cameras with EMG.
These recordings of muscle patter were gathered at two separate occasions. 21 after the
occurrence of ACL injury the first experiment was conducted. The knee was seen to be swelling
and also had a limit in range of motion and limit in the capacity of force development. In the first
experiment conducted, EMG electrodes were placed on rectus femoris, vastus lateralis, vastus
medialis, biceps femoris, and semitendinosus of both legs to enable comparing of lateral versus
medial muscle activity.
In the second experiment, a dynamic range of motions were examined and motions performed in
the first experiment were tried for a second go. The motions studied were:
Gait, the subject was made to walk in a straight path at a median pace
3.3 Experimental procedure
3.3.1EMG testing
Pre testing, the skin had to be prepared and the placement of electrodes had to be checked
properly.
The removal to body hair had to be done first to improve the adhesion of electrodes and the
conduction. A cleaning process with alcohol was performed on the body to remove dead skin and
dirt to lower the electrical impedance. Placement of electrodes on the prepared site. A coating of
a gel was put on electrodes with conducting properties and low impedance. The positioning of
electrodes can be done an optional basis with guidelines and recommendations of Seniam project
(Surface Electromyography for the Non-Invasive Assessment of Muscles) of the European
Union can be followed (SENIAM, 1999).
With use of double sided take wireless transmitters were connected to the electrodes and attached
to the skin. Registered data from the electrodes was amplified and then sent to the EMG system
connected to computer which is installed with software Vicon Nexus. There may be invalid
signals caused due to high sensitivity of transmitters when external forces cause sudden
movement. To prevent or minimize these external interference transmitters were stabilized using
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straps. The placement of the transmitters and electrodes on the body for experiment one has been
illustrated in the figure 3.1. After the EMG electrodes are positioned and properly connected,
positioning is verified by active movements.
Figure 3.1. EMG electrodes and transmitters have been attached to the biceps femoris and the
semitendinosus of the hamstrings. The transmitters on the left leg are stabilized by using straps
while the transmitters on the right leg are kept visible.
Measurements of the recorded frequency of EMG was 1000 Hz, The collected data points
represents a time interval of 1 ms and the potential difference in volts were measured in the
numerical value of the point.
3.3.2 Maximum Voluntary Contraction
To provide the reference value for the normalization of the second experiment during
performance of each muscle the maximum voluntary contraction was performed. Recording of
each muscle was done during one maximal manual isometric muscle test for ten seconds
approximately. The special designed chair of stabilization was the main subject that was strapped
tightly, the knee joint were fixated at an angle of 80 degree approximately and the ankles were
positioned close to neutral position. The action of bilateral isometric muscle which is the test for
both the legs simultaneously for each muscle group was executed from the measurements of
MVC. There were no MVC test made during the first experiment. The knee had not recovered
from recent trauma prevented testing of isolated knee there was an extension at higher stress
levels.
3.4 Signal Processing Method
First the motion data need to be rectified for the better influence of any systematic error,
The baseline had to be c centred. The mean value of the data measured for each muscle from
each measurement was subtracted from each respective set of the data points. This resulted in
shifting the mean value of the data points to be equal to zero, which shows that the offset has
been removed and the baseline has been centred. The rectification of MVC and relaxation data
was done well.
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For using equation 2 the background noise was responsible, the relaxation data the RMS
value is found. The algorithm which were used for removing the background noise the data point
was studied by motion data set separately and set every data point smaller than the RMS value to
zero. The data points greater than the value of RMS were decreased by the value of RMS value.
Due to the sampling frequency being 1000 Hz , the Nyquist frequency of the signal
sampling and the maximum expected signal frequency are both 500 Hz. Consequently, the raw
EMG data cannot contain frequency above 500 Hz and the use of a band pass filter would be
superfluous. Instead, a high pass filter with a cut off frequency of 10 Hz (based on literature
recommendation, section 2.2.2) was applied. Built in high pass filter in Matlab, called butter, was
used to create a transfer function able to filter the EMG data. The transfer function was of the
form :
where n is the order of the filter. Different filter orders were tried in an attempt to find the
minimum order required for sufficient filtering. The EMG data was transformed using the
designed transfer function and the Matlab function filt-filt.
Where is w the window size and T is the total number of the data points in the data set. Equation
(5) and (6) were used for the first w/2 -1 and the last w/2 data points, where a window of full
size could not be used.
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