Download EMG-Reflex Device Report

EMG-Reflex Device
BIOE 385: BIOINSTRUMENTATION LABORATORY
Erik Hansen, Ronal Infante
Table of Contents
Introduction ............................................................................................... 3
Summary ............................................................................................................................. 3
EMG-Reflex Device ........................................................................................................... 4
Instructions ............................................................................................... 6
Hardware Set-up ................................................................................................................. 6
Test Subject Preparation ................................................................................................... 10
Recording a Measurement ................................................................................................ 12
Safety Information ............................................................................................................ 14
Troubleshooting ................................................................................................................ 15
Device Limitations .................................................................................. 16
Technical Specifications ........................................................................ 17
DB9 Male Connector ........................................................................................................ 18
Hammer Inverting Amplifier ............................................................................................ 20
Electrical Isolation Circuits............................................................................................... 21
EMG First Stage Instrumentation Amplifier .................................................................... 22
EMG Passive Band-pass Filter ......................................................................................... 23
EMG Second Stage Inverting Amplifier........................................................................... 24
LabVIEW Code ........................................................................................ 25
Front Panel ........................................................................................................................ 25
Block Diagram .................................................................................................................. 25
Design Challenges .................................................................................. 27
References .............................................................................................. 28
Appendix ................................................................................................. 29
Troubleshooting Figures ................................................................................................... 29
Bode Plot ........................................................................................................................... 30
Front Panel Figures ........................................................................................................... 31
Block Diagram Figures ..................................................................................................... 34
1.
Introduction
Summary
The human body has three types of muscles: cardiac muscle, smooth muscle, and skeletal muscle.
While the first two types are found mostly in organs, skeletal muscles are attached to bone and
facilitate movement.
Fig. 1. A diagram depicting a reflex arc and sensory and motor neurons [1].
Afferent sensory neurons and efferent motor neurons are central to skeletal muscle function
throughout the body. Sensory neurons transmit electrical impulses in the form of action
potentials, or temporary membrane potentials along the length of cells, from a receptor (such as
the skin) to the spinal cord. Motor neurons receive these impulses from the spinal cord and
prompt skeletal muscle contraction (Fig. 1). It is not always required for the impulses to reach
the brain. In areas of high sensitivity or when strong stimuli are detected [2], impulses travel
straight from the sensory neurons to the motor neurons through an association neuron (also
called an interneuron), forming what is known as a reflex arc, and a reflex is produced.
A motor unit is comprised of a single motor neuron and all of the muscle fibers it controls [3].
When a motor neuron delivers an impulse, the muscle fibers in the motor unit respond by
generating their own electrical signals that lead to contraction. These electrical signals, in the
form of weak electrical potentials or voltages, may be detected on the overlying skin using
surface electrodes. The process of detecting and amplifying skin voltages of underlying muscle
contraction is called electromyography and the recordings are called electromyograms (EMGs).
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EMG-Reflex Device
Our EMG-Reflex device records patient reflex time by measuring the difference in time between
a hammer tap to the patellar tendon and the resulting knee-jerk reflex. When the hammer taps the
patellar tendon, a resulting electrical signal is sent from the hammer to our device and the time of
hammer impact is recorded. Upon tapping the patellar tendon, muscle spindles within the
quadriceps act as receptors and send an electrical impulse to the spinal cord along afferent
sensory neurons. Immediately, the efferent neurons respond by sending an electrical impulse
back to the quadriceps, causing the muscle to contract and thus extend the lower leg. This
reflexive contraction is commonly referred as the knee-jerk reflex (Fig. 2).
Fig. 2. A visual representation of the knee-jerk reflex [4].
Then, two electrodes placed along the length of the quadriceps record the voltage produced by
the returning efferent impulses along the muscle. The voltage is then amplified, filtered, and
sampled past a threshold value. The resulting EMG time is recorded and the difference between
the two times is calculated, recorded, and displayed.
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Clinical studies indicate that the average knee-jerk reflex time is about 21 milliseconds [5].
Significant deviation from this average could indicate a damaged central nervous system.
Therefore, implementation of our device allows for detection of neurodegenerative diseases or
neuromuscular disorders, such as Amyotrophic Lateral Sclerosis or Becker Muscular Dystrophy.
Our device is built using a reflex hammer to produce the initial signal, alligator-banana cables
and electrodes to detect EMGs, and simple electrical components, such as resistors, capacitors,
diodes, and operational and instrumentation amplifiers, to amplify and filter the resulting signal.
Therefore, it is quite cost-effective to manufacture. A LabVIEW virtual instrument (VI) provides
an intuitive user interface and further signal processing to reduce noise. In addition to being costeffective, our device takes patient safety in consideration by including electrical isolation
circuitry that prevents microshock. Because skin surface electromyography is non-invasive, it
proves to be a painless alternative to needle-based approaches. By following the simple
instructions detailed below, any user will be able to successfully set up and operate our device.
The implementation of our device would be cost-effective, intuitive to use, and would improve
patient outcomes.
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2.
Instructions
Hardware Set-up
1. Turn on the National Instruments Elvis (NI ELVIS). The system power button is found
on the back (Fig. 3). Also make sure the power cable of the NI ELVIS unit is plugged in
securely.
Fig. 3. The back of the NI ELVIS unit showing the system power button (left) and
the power cable (right).
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2. Turn on the prototype board power. The prototype board power button is found on the
front (Fig. 4). The lights for the system power and the prototype board power should be
shining.
Fig. 4. The front of the NI ELVIS unit showing the prototype board power
button and the two lights.
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3. The NI ELVIS unit’s connector is found on the top of the unit towards the back (Fig. 5).
Slide the prototype circuit board into the NI ELVIS unit’s connector. The prototype board
should snap tightly into the connector.
Fig. 5. Placing the prototype circuit board into the NI ELVIS unit’s connector.
4. Our device is built to function with Hammer G. Find Hammer G (Fig. 6).
Fig. 6. Hammer G.
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5. Connect Hammer G’s male pin connector to the female pin connector wired to the circuit
board (Fig. 7).
Fig. 7. Connecting Hammer G’s male pin connector to its corresponding female pin receptor.
6. Collect two alligator-banana cables. Plug them into the Banana A and Banana B ports on
the top right part of the circuit board (Fig. 8).
Fig. 8. The Banana A and Banana B ports with cables plugged in.
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Test Subject Preparation
1. Collect two electrodes. Since electrical activity of muscle is to be measured, place them
about 2 inches apart along the length of the quadriceps with significant muscle mass (Fig.
9). Attach the alligator ends of the Banana A and B cables to the electrodes. Since the
device measures a potential difference along the length of the muscle, it does not matter
which electrode you connect the banana cables to.
Fig. 9. The two electrodes in position along the length
of the quadriceps with banana cables attached.
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2. The subject should sit comfortably in a relaxed position. Any voluntary tension in the
muscle group will produce inaccurate results. Raising the chair and letting the patient’s
legs hang off of the edge of their chair is a good way to prevent voluntary tension (Fig,
10).
Fig. 10. Hanging legs off of your chair can help prevent voluntary tension.
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Recording a Measurement
1. Turn on the computer. Locate and open the VI file (Fig. 11). LabView should initialize.
Run the VI (Fig. 12).
Fig. 11. Selecting the VI file.
Fig. 12. The run button (left) after it has been pressed to run the VI file.
The stop button (right) stops the VI file from running.
2. On the VI’s Record EMG-Reflex tab, select the Calibrate Device button and wait for the
device to calibrate (Fig. 26). An error will appear if there is too much noise. If so, try
recalibrating. To reduce noise, try braiding the alligator-banana cables.
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3. Tap the patellar tendon with the hammer (Fig. 14). The patient should be fully relaxed
and not tapping their own tendon. Otherwise, voluntary tension might occur and reflex
time will be inaccurate. You should observe a knee-jerk reflex.
Fig. 14. The process of tapping the patellar tendon with Hammer G.
Electrodes and alligator-banana cables are securely attached.
A second individual should be tapping the patient’s tendon.
4. The knee-jerk reflex must occur for accurate reflex time measurement. If the knee-jerk
reflex does not occur, try tapping the patellar tendon with more force. Alternatively,
engage in the Jendrassik maneuver (Fig. 23).
5. If the EMG signal passes the threshold value, reflex time is calculated and displayed. If
the knee-jerk reflex occurred, press the Add Measurement to Table button (Fig. 26). This
places the reflex measurement in the Table of Results.
6. To remove an erroneous measurement, enter the corresponding row number into the
indicator. Press the Remove Measurement form Table button (Fig 26).
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7. Repeat steps 2 and 3 to acquire as much data samples as required. The Save Table button
exports the table to an Excel file (Fig. 26).
Safety Information
When operating the device, please consider the following safety procedures:

Our device features two electrical isolation circuits, one for each incoming lead, as
barriers to prevent high currents from flowing back into the body from the device,
causing macroshock. If high currents attempt to flow through the diodes, they will burn
out and serve as circuit breakers, saving you from dangerous shock. If these were to burn
out, immediately turn off all power to the device.

If you smell burning or experience any form of shock when handling the device, a
component might have malfunctioned. Turn off all of power and seek technical help.

Refrain from hitting the hammer with excessive force as it may break.

Do not tamper with the prototype board’s circuitry as it may expose you to shock hazards,
produce inaccurate results, or compromise the isolation circuits.

Do not consume food or beverages near the device to prevent spills. Wet environments
lead to equipment failure.

Always handle the device with dry hands. Moisture reduces the resistivity of the skin and
increases the risk of microshock.
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Troubleshooting
If there seems to be an issue with the device, consider the following common solutions:

Make sure the ELVIS system and the prototyping board are both powered on. Lights on
the front of the unit will indicate if both are powered (Fig. 4).

Double check to make sure the prototype circuit board is securely connected to the NI
ELVIS unit (Fig. 5).

Make sure all three green lights on the bottom left of the prototype circuit board are
turned on (Fig. 24). If not, the NI ELVIS unit has blown a fuse and it must be replaced in
order to proceed.

Make sure you are using Hammer G (Fig. 6). Not all Hammers are guaranteed to work
with our device.

Make sure the male and female pin connector/receptor pair for Hammer G is connected
securely (Fig. 7). Examine the prototype circuit board to confirm that the female pin
receptor has not unwired itself from the board.

Confirm that the electrodes are in contact with the quadriceps muscle and that the
alligator-banana cables are securely connected to the electrodes (Fig. 9). Use tape to
secure the electrodes if necessary.

If you are acquiring too much noise, try the following tricks:
o Performing the Jendrassik maneuver (Fig. 23) by cupping and pulling on your
hands will enhance the patellar reflex by inhibiting descending brainstem inputs
that would inhibit reflex arc interneurons [6].
o Additionally, braiding the alligator-banana cables reduces noise by canceling out
the interference produced by the magnetic fields created by running current
through wires.
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3.
Device Limitations
While our device measures consistent reflex times that agree with clinically determined values, it
is still limited and has the potential for improvement.
Our design only implements 2 electrodes and uses the machine ground as reference. Machine
ground is not ideal when dealing with biological noise as it is out of context. Therefore, it is
possible that our device is limited by additional noise that can be eliminated via adding a third
electrode placed on the patellar bone. Future versions of our device would benefit from the
addition of a third electrode. This addition has the potential to remove unwanted noise by
providing a biological ground that we may reference to. Since it experiences similar biological
noise to our other electrodes, the measured voltage will be free from this noise due to the relative
measurement.
Additionally, our device is only optimized to detect EMG in the quadriceps in response to
patellar tendon stimulation. For a better diagnosis of neurodegenerative diseases or
neuromuscular disorders, a whole body assessment of reflex times could be employed. Currently,
our device is not that sophisticated. Future versions of our device would benefit from the
addition of a feature that allowed you to choose the reflex you want to measure. Perhaps the user
could be given a list of reflexes to choose from. Upon choosing, optimized filtration and
amplification settings could be applied to the VI for accurate and consistent measurements of a
range of reflex types.
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4.
Technical Specifications
The following block diagram describes the general mechanics of our device:
Fig. 15. Block diagram of our device.
Ultimately, two channels of data will feed into LabVIEW for analysis and recording, one from
the reflex hammer and another from the electrodes.
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DB9 Male Connector
The reflex hammer is connected to our device via a DB9 Male Connector. The male pin
connector has 9 total pins, only five of which are used by our device. The pin connector was
soldered onto colored wires. Each pin number its corresponding data and wire color are listed in
the table in Figure 17. The input power supplies are wired to pins 6 and 9. The +5V is wired
from the DC supply of the prototype board. The -5V supply is provided by the LabVIEW code.
Since the hammer is not in contact with the body for a prolonged period, it requires neither
electrical isolation circuits, nor filters to remove biological and ambient noise. Pins 2 and 4 are
the outputs of the hammer and the inputs to the OP07 hammer amplifier. To reference the output
signal of Hammer G, pin 4 is grounded. Pin 3 is wired to ground and the other four pins are
unused. We opted not to use shielding because we are inexperienced solderers. While shielding
can provide more noise reduction, doing it incorrectly would have introduced much more noise.
After getting a working prototype we decided that noise levels were low enough to justify not
adding shielding.
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Fig. 16. Pin diagram of the male DB9 connector.
Pin Number
Data Carried
Wire Color
1
Shield
Not Used
2
Vin+
Green
3
Ground
White
4
Vin- (ground)
Orange
5
Shield
Not Used
6
+5V (ref)
Red
7
None
Not Used
8
None
Not Used
9
-5V (ref) (DAQ0)
Blue
Fig. 17. A table listing the DB9 male pin connector’s pins and their function in circuitry.
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Hammer Inverting Amplifier
The signal produced by the hammer undergoes amplification (Fig. 18). The hammer voltage
signal comes from the pins 2 and 4 of the male pin connector. The amplifier is composed of an
OP07 differential amplifier in the inverting configuration with 110Ω and 220kΩ resistors and a
gain of -2000.
𝐺𝑎𝑖𝑛 = −𝑅𝑓/𝑅𝑖𝑛 = −220000/110 = −2000.
The amplifier is powered by +15V and -15V DC supplies on the prototype board. The output of
the amplifier is then connected to LabVIEW through an ACH port on the prototype board.
Fig. 18. Reflex hammer OP07 amplifier configuration.
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Electrical Isolation Circuits
The two electrical isolation circuits, one for each incoming lead, protect the test subject from
macroshock by acting as barriers to prevent high currents from flowing back into the body from
the device (Fig. 19). First, the inputs from the electrodes enter the prototype board through both
banana cables. Both electrical isolation circuits are comprised of 10kΩ resistors and 2 (MFG#
1N4148) diodes. The 10kΩ resistor forces the current down to 60μA, well below the current
safety threshold. If the device sends voltages over 0.6V and high currents attempt to flow
through the diodes, they will burn out and serve as low impedance circuit breakers, directing
harmful current to ground and saving you from dangerous shock.
Fig. 19. One of the two electrical isolation circuits. Both are identical.
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EMG First Stage Instrumentation Amplifier
Both isolation circuits then feed into an AD620 instrumentation amplifier (Fig. 20). The
amplifier is powered with +15V and -15V DC supplies from the prototype board. The difference
in voltage between the two terminals is amplified when the signal from the Banana B is
arbitrarily lead into the positive terminal and the signal from Banana A is lead into the negative
terminal. Using a 1kΩ resistor, the gain of this amplifier is 495. We used the more sophisticated
instrumentation amplifier for the first stage amplification of the EMG signal because it amplified
a foundational signal with less noise than the OP07 operational amplifier.
𝐺 = 1 + (49400/𝑅𝑔) = 1 + (49400/100) = 495.
Fig. 20. The AD620 Instrumentation Amplifier
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EMG Passive Band-pass Filter
After the first stage amplifier, the EMG signal is filtered to remove both low and frequency
components (Fig. 21). According to De Luca, Carlo J., et al., surface EMG signals should be
filtered between 20 Hz and 450 Hz [7]. Using two 33μF capacitors and 10Ω and 220Ω resistors,
the approximate cutoff frequencies for our passive band-pass filter were 22Hz and 482Hz.
Frequencies above and below these frequencies were attenuated, as shown by bode plot analysis
(Fig. 25).
𝐶𝑢𝑡𝑜𝑓𝑓 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = 𝑓𝑐 = 1/(2 ∗ 𝑝𝑖 ∗ 𝑅 ∗ 𝐶)
Fig. 21. The passive band-pass filter with cutoff frequencies
of approximately 22 and 482Hz.
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EMG Second Stage Inverting Amplifier
After undergoing filtration, the EMG signal is attenuated. A second round of amplification using
an OP07 operational amplifier and 100Ω and 3kΩ resistors provides -30 gain to the EMG signal
(Fig. 22).
𝐺𝑎𝑖𝑛 = −𝑅𝑓/𝑅𝑖𝑛 = −3000/110 = −30.
Fig. 22. The second OP07 Inverting Operational Amplifier.
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5.
LabVIEW Code
Front Panel
The front panel of our VI features 3 tabs each with very intuitive navigation: a welcome tab, the
reflex time recording tab, and a troubleshooting tab (Figs. 26-28). There are buttons to move
between tabs and to stop the VI. On the Record EMG-Reflex tab, calibration is visually
confirmed by a progress bar as well as a bright button. Both the EMG signal and Hammer G’s
signal are visualized on a large graph. Numerical indicators show impact time for each signal
type in exact real time. The reflex time is calculated from these variables and is displayed with
units. Adding values to the table of results is very intuitive. A save table button allows the user to
export their saved data into an Excel file. On the Advanced tab, various troubleshooting graphs
and indicators are available to view. There are graphs showing unfiltered signals and the filtering
intervals in both time and frequency domains. The calibrated threshold is displayed to the user as
well as a confirmation of the DC input to the Hammer for pin 9.
Block Diagram
The block diagram codes for all of the code block functions of the VI:
Outside the main while loop, many values are reset in case the VI is stopped, the Table of
Results is initialized, and within its own independent while loop, -5V is sent to pin 9 of the
Hammer (Fig. 29).
Just inside the while loop, before the large case structure that holds much of the tab-dependent
code, the stop conditions are coded, taking in booleans from the Stop VI buttons on each front
panel tab (Fig. 30). The EMG signal and the Hammer signal are read and converted from analog
data to digital data through the use of the DAQ function block. The signals are separated and the
EMG signal runs through a SubVI titled Notch Filters that holds the code for two 60 Hz notch
filters, the original noise and one harmonic at 120 Hz (Fig. 31). Both dynamic data types are
converted into waveform data types. The time data is separated and sent to the tab case structure.
Gains are given to each signal based on experimental values.
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When sent into the Record EMG-Reflex tab, the data is stored into an array and visualized on the
large graph along with the threshold if it’s been stored (Fig. 32). The threshold is calculated
when the Calibrate button is pressed (Fig. 33). Before calibration much of the front panel is
disabled. During calibration the progress bar moves and resting noise data is stored into an array.
After 10,000 values are stored, a maximum value is determined and 1 is added to establish a
solid EMG threshold. If the threshold is greater than 5V (indicating max noise at 4V), then
calibration will fail due to large amounts of noise. A message is displayed when calibration has
either successfully been completed or when it has failed. If it fails, the user is prompted
recalibrate and much of the front panel remains disabled.
The EMG signal is compared to this new threshold value and the Hammer signal is compared to
a threshold value of 1V (Fig. 34). The indices where the amplitude data crosses each threshold is
calculated and if the default value of 99 is not returned, these indices are used to index the time
data that was previously separated. If the indexed Hammer time is not larger than the indexed
EMG time (which would result in a negative time difference), then the respective times are
stored in numeric indicators. Once stored, reflex time is immediately calculated by taking the
difference between the two times. Since reflex time is displayed in milliseconds, the difference is
multiplied by 1000.
The remaining code on the block diagram produces the aesthetics of the front panel (Fig. 35).
These include concatenating new values onto the Table of Results when the Add Measurement to
Table button is pressed, the removal of indices from the Table of Results when the Remove
Measurement from Table button is pressed, and array building for Excel report generation.
Code on the remaining case structure tabs, such as the Advanced tab, provides for the storage of
data into numerical indicators and for the function of buttons (Fig. 36).
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6.
Design Challenges
The most important challenge to consider when dealing with living systems is electrical safety.
Our device requires the use of 2 electrodes placed against the human body, contact points for
macroshock. The electrical isolation circuits protect the patient from this threat.
Blocking out biological and ambient noise was the next big design challenge. The body has
various electrical signaling pathways that produce undesirable electrical noise. Therefore,
filtration is required to isolate the desired signal. We decided to address this issue with the
passive band-pass filter displayed in the Technical Specifications that features ideal cutoff
frequencies supported by literature. Interactions with non-living systems, such as the noise from
60 Hz household electric power supply and its harmonics, can be also be eliminated by filtering.
We addressed these issues with two high-ordered notch filters with cutoff frequencies at 60 Hz
and the 120 Hz harmonic. This was enough to reduce noise.
Differences in test subject are another issue that must be taken into account. Humans have many
characteristics that make us physiologically unique. These characteristics make sampling data
challenging because fixed parameters don’t work for everyone. An ideal device must adapt to
these differences and produce accurate and consistent results for every test subject. We addressed
this issue by adding a calibration feature to our device. For 10 seconds, our device stores resting
EMG data. Then, the data is analyzed for a max resting noise value and the EMG threshold value
is adjusted. This prevents noise from triggering the recording and successfully allows us to
personalize the device to the individual’s noise level.
Whether or not to allow the device to adapt to different locations in the body is another design
challenge that we addressed. Different parts of the body have varying levels of biological noise
and muscle mass. Our device is optimized for use on the patellar tendon, taking measurements
from the activated muscle fibers in the quadriceps muscle. If we were to allow our device to be
compatible with multiple sites in the body, we would need to develop a method of optimizing the
filtering and amplification of EMG signals for a dynamic location. Since this proves too
challenging, we did not add this feature.
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7.
References
[1]
TheFreeDictionary.com. "Achilles Reflex." Farlex, n.d.
<http://medical-dictionary.thefreedictionary.com/Achilles+reflex>.
[2]
The Columbia Electronic Encyclopedia, 6th ed. (Columbia University Press, New York,
2000).
[3]
Biopac Systems Inc. "Biopac Student Lab Manual." (1998).
[4]
"Knee Jerk Reflex Pathway." Edoctoronline.com. EDoctorOnline.com, n.d.
<http://www.edoctoronline.com/medical-atlas.asp?c=4&id=21800>.
[5]
Frijns, C. J. M., et al. "Normal values of patellar and ankle tendon reflex latencies."
Clinical neurology and neurosurgery 99.1 (1997): 31-36.
<http://www.sciencedirect.com/science/article/pii/S0303846796005938>.
[6]
Biopac Systems Inc. “BSL PRO Lesson H28: Reflex Response (Patellar Tendon) Using
BIOPAC Refex Hammer Transducer SS36L.” (2006).
[7]
Luca, Carlo J. De, Gilmore, L. Donald, Kuznetsov, Mikhail, Roy, Serge H., “Filtering the
surface EMG signal: Movement artifact and baseline noise contamination.” Journal of
Biomechanics 43.8 (2010): 1573-1579.
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8.
Appendix
Troubleshooting Figures
Fig. 23. The Jendrassik maneuver.
Fig. 24. The prototype board’s 3 fuse lights.
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Bode Plot
Fig. 25. Bode plot showing the frequency range of our band-pass filter with
cutoff frequencies of 10.6 Hz and 530 Hz.
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Front Panel Figures
Fig. 26. The Welcome screen of the front panel.
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Fig. 27. The Record EMG-Reflex screen of the front panel.
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Fig. 28. The Advanced screen of the front panel.
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Block Diagram Figures
Fig. 29. Initializing code.
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Fig. 30. The code before the tab case structure.
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Fig. 31. The code within the subVI.
Fig. 32. Visualizing the two signals and threshold.
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Fig. 33. Calibration and the calculation and storage of a threshold.
Fig. 34. The calculation of reflex time.
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Fig. 35. The remaining code on the Record EMG-Reflex tab that codes for the table and the
buttons.
Fig. 35. The remaining code on the Advanced tab.
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Fig. 36. The entire block diagram as a reference.
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