ARIEL EMG PROGRAM
One
of the most intriguing and challenging areas of study in biomechanics is
probably the muscle itself. The
electrical signal associated with the contraction of a muscle is called an
electromyogram or, by its shorthand name, EMG.
Electromyography is the study of muscle activity by measuring these
electrical signals. Clinicians and
researchers have applied the study of EMGs to the fields of neurology, surgical
assessments, functional capacity evaluations, ergonomics and overuse injuries,
and chronic pain evaluations, just to name a few.
In
addition to the extensive EMG analysis options found in the Analog module of
the Ariel Performance Analysis System
(APAS), the Ariel EMG program provides additional
capabilities. The ARIEL EMG software is a Windows based program for calculating the
integral and normalizing the EMG signal in both time and amplitude. An
understanding of the electrophysiology
and the technology of recording is recommended for optimal use of the EMG
program.
Although
a few of EMG’s features appear
complex, they are relatively easy to master once you understand the underlying
concepts. This manual is arranged to
teach you these concepts in a logical order by showing you, in step-by-step
fashion, how to use the EMG
program.
A
few of the new features you will see in EMG version 1.0
1.
EMG Signal Normalization. EMG signals can be normalized in both Time
and Amplitude.
2.
EMG Signal Integration. EMG signals can be integrated using several
parameters.
The
following list provides the basic guidelines for the necessary components of
the EMG program to provide the best possible performance. The software requires a minimum of Microsoft
Windows 95/98 or later and APAS-2000 Revision 1.0 or later (with the
EMG/Analog).
1.
Ariel Performance Analysis System (APAS) software used to collect EMG
data in *.ANA file formats.
Prior
to performing the EMG analysis
process, you should take the time to familiarize yourself with the format and
contents of the various screens listed below:
THE TOOL BAR
You
can activate many functions by selecting the icons located on the EMG program tool bar. The tool bar is located near the top of the
window. Icons are pictorial
representations of commands or functions.
You can access the following commands by clicking the appropriate icon.
THE EMG WINDOW LAYOUT
When
an EMG file is opened, additional windows will be displayed inside the
main window. Multiple windows can be opened simultaneously. The EMG
Title will be displayed at the top of each active Window.
THE STATUS BAR
The
status bar provides information about the current EMG analog file. The status bar is located at the bottom of
the EMG window.
The
far left side of the status bar indicates the current status of the EMG
file. This field will usually state READY.
The far right side of the status bar displays the currently selected
analog (*.ANA) file.
1.
Double-click the EMG icon
located in the APAS System window
group. The main EMG window will appear.
The
following steps are recommended for correct operation of the EMG program.
1.
Choose the NEW command from the FILE menu. This will open a new *.EMG document with an empty list of EMG
data sets. A grid with 8 columns
appears to display the active sample list.
2.
Select the ANALOG command
from the FILE menu to specify
an Analog (*.ANA) file for retrieving
data sets. This selection can be
changed at any time.
3.
Click on the NEW button below
the “grid” and select a Save Trial and Channel from the active Analog
file. Select the OK button to enter the selected data set to the active data set
display.
4.
Repeat Step #3
to select all data sets of interest.
5.
Mark
individual entries as either active or inactive by clicking in the 1st
column of the grid. Active channels
will be graphed and displayed for analysis.
If an entry is active, a "=>"
will be displayed in the first column.
If an entry is inactive, the first column will be blank. If the user selects FILE, SAVE AS and there
are disabled channels, the program prompts the user whether or not to save
disabled channels.
6.
Mark an
individual entry as the Maximum Voluntary Contraction (MVC) by clicking the 2nd
column of the grid. The Maximum
Voluntary Contraction channel is the channel where the subject has performed a
maximum contraction. Marking a channel
at the MVC is only required for normalizing using the MVC option.
7.
Mark an
individual entry as the Trigger channel by clicking the 3rd column
of the grid. The Trigger channel is
used in partitioning data. It typically
is not an EMG channels but rather some other signal which helps one partition
the EMG data. An example would be a
switch opening/closing to define an activity of interest.
NEW - This button
is selected to add a save trial from the currently active analog file.
DELETE - This button
is selected to remove a save trial from the analysis table.
ENABLE ALL - This button is selected to
ACTIVATE All the Save Trials in the analysis table.
DISABLE ALL - This button
is selected to INACTIVATE All the Save Trials in the analysis table. Disabled channels will not be graphed.
PARTITION - This button
is selected to Partition the selected entries.
At
this point, the program is ready to Graph the EMG data.
PARTITION
When
sampling EMG activity, it is often useful to analyze specific intervals of the
entire signal. The Partition option
allows the user to partition an EMG signal into smaller intervals for analysis. Multiple curves can be simultaneously
partitioned. The following steps are
recommended for partitioning an EMG signal.
1. Select the
PARTITION button to display the Partition Channel menu.
2. Select the
CHANNELS button to specify which data channels are active during the
partitioning. Individual channels are
selected by clicking in the Status column next to the desired channel. All channels can be activated by selecting
the Select All button. All channels can
be deactivated by selecting the Clear button.
Select OK to proceed.
3. Select the
desired partition by clicking the left mouse button and dragging the cursor to
highlight the desired partition. The
partition will be seen as an alternate color.
4. Select the Add
button to enter the data in the partition list. Repeat step #3 for additional partitions.
5. Select OK to
return to the data entry table. The
partition information will be updated in the table.
Once
the desired trials have been entered into the table, activated and partitioned
(if desired), the data can be graphed utilizing several analysis options.
1. Select the GRAPH
menu to display the available graphing options for the EMG data.
EMG
The
EMG command provides several options for graphing and analyzing the
"raw" EMG signal. When this
command is selected, the RAW EMG OPTIONS menu will be displayed.
GENERAL
X-Normalize - Selected to
normalize all selected graphs to the same time scale (X-axis). All the active graphs will be normalized to
the same time scale as the graph with the smallest time period.
AutoScale - Selected to
display the entire graph(s) with maximum resolution. The size of the graph remains constant, regardless of the size of
the display window.
Fit to Scale -
Selected
to display the entire graph regardless of the size of the window. If the window size is adjusted, the graph
will also adjust to fit the new size of the window.
Rectify - Selected to
perform a full-wave rectification on the "raw" EMG signal.
Maximize - Selected to
enlarge the window to the maximum size.
Y-NORMALIZE
None - Selected to
display the graph(s) without Y-Normalization being performed.
MaxPeak - Selected to
normalize all the curves so that all curves will have a peak value for the
envelope equal to the curve which un-normalized had the largest envelope value.
%Mode - Selected to
scale each curve so that the peak value for the envelope curve is 100%.
100% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 100% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 100% normalization has been selected, then
other channels would be normalized so that their peaks would be 4.0 mv.
50% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 50% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 50% normalization has been selected, then
other channels would be normalized so that their peaks would be 2.0 mv.
CURVES
Raw + LE - Selected to
graphically display the Raw data curve as well as the computed Linear Envelope
(LE) curve.
Raw Only - Selected to
graphically display only the Raw data curve.
LE Only - Selected to
graphically display only the computed Linear Envelope curve.
PIXEL MODE
Due
to the high sampling rate of EMG signals, one pixel often corresponds to many
A/D samples. The number of data points
are divided by the available pixels to determine the number of data points
represented by each pixel. Each
"set" of pixels can be represented in various ways.
1st
- Selected
to use the First data point of each group to represent the entire group.
Max - Selected to
use the Maximum data point of each group to represent the entire group.
Avg - Selected to
use the computed Average of all the data point of each group to represent the
entire group.
LE TIME (sec)
This
field is used to enter the time interval for the Linear Envelope (LE). The LE is used to remove rapid signal
fluctuations by averaging over an interval that is longer than the duration of
individual "spikes" or fluctuations.
It is similar in nature to a low-pass analog filter. The longer the time constant, the lower the
cutoff frequency of this filter. Some
experimentation may be necessary, however, a default value of 0.1 seconds will
be displayed.
AVG/RMS
The
AVG/RMS command provides several options for graphing and analyzing the Average
EMG signal. When this command is
selected, the AVG/RMS GRAPH OPTIONS
menu will be displayed.
GENERAL
X-Normalize - Selected to
normalize all selected graphs to the same time scale (X-axis). All the active graphs will be normalized to
the same time scale as the graph with the smallest time period.
Fit to Scale -
Selected
to display the entire graph regardless of the size of the window. If the window size is adjusted, the graph
will also adjust to fit the new size of the window.
Maximize - Selected to
enlarge the window to the maximum size.
Y-NORMALIZE
None - Selected to
display the graph(s) without Y-Normalization being performed.
MaxPeak - Selected to
normalize all the curves so that all curves will have a peak value for the
envelope equal to the curve which un-normalized had the largest envelope value.
%Mode - Selected to
scale each curve so that the peak value for the envelope curve is 100%.
100% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 100% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 100% normalization has been selected, then
other channels would be normalized so that their peaks would be 4.0 mv.
50% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 50% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 50% normalization has been selected, then
other channels would be normalized so that their peaks would be 2.0 mv.
LE TIME (sec)
This
field is used to enter the time interval for the Linear Envelope (LE). The LE is used to remove rapid signal
fluctuations by averaging over an interval that is longer than the duration of
individual "spikes" or fluctuations.
It is similar in nature to a low-pass analog filter. The longer the time constant, the lower the
cutoff frequency of this filter. Some
experimentation may be necessary, however, a default value of 0.1 seconds will
be displayed.
INTEGRAL
The
INTEGRAL command is selected to perform one of several types of integration on
the EMG signal. These integration
options produce data curves representing the integrl or area under the input
curve in different formats. When this
command is selected, the INTEGRAL
OPTIONS menu will be displayed.
GENERAL
X-Normalize - Selected to
normalize all selected graphs to the same time scale (X-axis). All the active graphs will be normalized to
the same time scale as the graph with the smallest time period.
AutoScale - Selected to
display the entire graph(s) with maximum resolution. The size of the graph remains constant, regardless of the size of
the display window.
Fit to Scale -
Selected
to display the entire graph regardless of the size of the window. If the window size is adjusted, the graph
will also adjust to fit the new size of the window.
Maximize - Selected to
enlarge the window to the maximum size.
Y-NORMALIZE
None - Selected to
display the graph(s) without Y-Normalization being performed.
MaxPeak - Selected to
normalize all the curves so that all curves will have a peak value for the
envelope equal to the curve which un-normalized had the largest envelope value.
%Mode - Selected to
scale each curve so that the peak value for the envelope curve is 100%.
100% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 100% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 100% normalization has been selected, then
other channels would be normalized so that their peaks would be 4.0 mv.
50% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 50% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 50% normalization has been selected, then
other channels would be normalized so that their peaks would be 2.0 mv.
RESET
Select
one of the following Reset options for integrating the signal.
None - Selected to
perform a summing integral or an integral with "No-reset." The curve value represents the cummulative
integral of the input channel and thus is a monotonically increasing curve.
Time - Selected to
perform a constant frequency resetting integral. The integral curve is cummulative for a specified
"Time" interval, then is reset to zero and begins accumulating
again. This produces a series of peaks
at a constant interval whose amplitude indicates the level of activity of the
EMG signal.
Value - Selected to
perform a constant amplitude resetting integral. The integral curve is cummulative until a specified
"Value" is reached, then is reset to zero and begins accumulating
again. This produces a series of peaks
at a constant amplitude whose frequency indicates the level of activity of the
EMG signal.
RESET TIME (sec)
This
field is used to enter the time interval for the Time Reset option.
RESET VALUE (mv-sec)
This
field is used to enter the value for the Value Reset option.
LE TIME (sec)
This
field is used to enter the time interval for the Linear Envelope (LE). The LE is used to remove rapid signal
fluctuations by averaging over an interval that is longer than the duration of
individual "spikes" or fluctuations.
It is similar in nature to a low-pass analog filter. The longer the time constant, the lower the
cutoff frequency of this filter. Some
experimentation may be necessary, however, a default value of 0.1 seconds will
be displayed.
POWER
The
POWER command is selected to perform a power spectrum analysis of the EMG data
signal. This analysis produces a graph
of power as a function of frequency based on a Fourier decomposition of the
analog signal. Power is defined as the
sum of the squares of the Fourier coefficients. Since the EMG signal consists of many component frequencies, this
type of anlysis provides an indication of the dominant frequencies and their
relative amplitudes within the composite signal. When this command is selected, the POWER GRAPH
OPTIONS menu will be displayed.
GENERAL
X-Normalize - Selected to
normalize all selected graphs to the same time scale (X-axis). All the active graphs will be normalized to
the same time scale as the graph with the smallest time period.
AutoScale - Selected to
display the entire graph(s) with maximum resolution. The size of the graph remains constant, regardless of the size of
the display window.
Fit to Scale -
Selected
to display the entire graph regardless of the size of the window. If the window size is adjusted, the graph
will also adjust to fit the new size of the window.
Amplitude - Selected to
perform an Amplitude analysis on the active channels. This analysis produces a graph of Amplitude as a function of
frequency.
Maximize - Selected to
enlarge the window to the maximum size.
Y-NORMALIZE
None - Selected to
display the graph(s) without Y-Normalization being performed.
MaxPeak - Selected to
normalize all the curves so that all curves will have a peak value for the
envelope equal to the curve which un-normalized had the largest envelope value.
%Mode - Selected to
scale each curve so that the peak value for the envelope curve is 100%.
100% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 100% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 100% normalization has been selected, then
other channels would be normalized so that their peaks would be 4.0 mv.
50% MVC - Selected to
perform the Linear Envelope of this data and normalize the other active
channels to the MVC channel. It is
often desired to normalize to 50% of this "maximum" contraction
value. For example, if the MVC channel
has a peak value (LE) of 4.0mv and 50% normalization has been selected, then
other channels would be normalized so that their peaks would be 2.0 mv.
MAX FREQ
Select the Maximum Frequency for the computation of the power spectrum. Only the power component frequencies below the maximum frequency will be reported. This allows t