Week 7: Muscle and EMG LabInstructions
Step 1. Download “BSL Analysis 4.1” – This is optional but it gives you the
opportunity to use Biopac for data analysis. Watch video from the following link:
following instructions, download software to your computer.
Step 2. Read “Introduction” section –on pages 2-3 of this document.
Step 3. Watch the EMG 1 Exercise – the data and explanation for this exercise are
found on page 4-5. This YouTube video demonstrates how the data is acquired from a
test subject: https://www.youtube.com/watch?v=Jix60_XnwjQ
Step 4. Watch the EMG 2 Exercise – the data and explanation for this exercise are
found on page 6-7. This YouTube video demonstrates how the data is acquired from a
test subject: https://www.youtube.com/watch?v=xQuoaaxMrMA&t=509s
Step 5: Questions and Discussion – answer questions starting on page 8. Please
hand in 1 copy per group and be sure to include the names of all active participants.
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Week 7: Muscle and EMG Lab
Step 2: Read Introduction
Electromyography (EMG) uses electrodes to
detect the electrical signal produced by your
skeletal muscle. All cells possess a distribution
of electrolytes that is usually more negative
inside the cell and more positive outside the cell
(Fig. 1). The movement of these electrolytes into
or out of the cell creates a detectable electrical
signal.
Fig. 2: Representative diagram of 2 motor
units controlling skeletal muscle fibers.
Fig. 1: Distribution of ions (electrolytes) across
the cell membrane.
Fig. 3: Release of acetylcholine and
depolarization of post-synaptic muscle.
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The process by which skeletal muscle generates an electrical signal begins with the
nervous system. All skeletal muscle is controlled by a special type of nerve called a motor
neuron. These motor neurons may be branched and can control several muscle cells
(fibers) (Fig. 2). A single motor neuron and all of the muscle fibers it controls is called a
motor unit. When a motor nerve is activated, it releases the neurotransmitter
acetylcholine, which binds to receptors on the muscle cell membrane (Fig. 3).
The next step in this process involves the cell membrane of the muscle cell. A cell
membrane is a specialized structure that surrounds the cell entirely. It is considered
selectively permeable due in part to its structure: it is composed of phospholipids (lipids
sandwiched between phosphate moieties). The phosphate moieties can interact with
water and electrolytes while the lipids avoid these interactions. Special protein channels
throughout the cell membrane allow electrolytes to move into or out of the cell.
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Week 7: Muscle and EMG Lab
When these electrolytes move into the muscle cell, they trigger a chain reaction.
Calcium, normally stored inside the cell, is released into the cytosol. This allows the
contractile proteins actin and myosin to interact and the cell shortens. The movement of
these electrolytes can be measured during electromyography. Interestingly, even when
your muscles are relaxed a small amount of ions cross the cell membrane maintaining a
slight state of contraction referred to as tonus.
Today, you will be evaluating two phenomena related to muscle contraction: fatigue
and motor unit recruitment. Motor unit recruitment refers to the increased electrical
signal observed when you increase the number of active motor units (Fig. 4). Think of
lifting a heavy book off your desk versus lifting a pencil in the exact same way. Your
body automatically activates more motor units for the heavy book and this is reflected
by a larger EMG signal. Alternatively, fatigue can reduce the electrical signal produced
by active motor units especially in untrained muscles. This is most likely due to the
motor nerves inability to generate a sustained signal.
Fig. 4: Motor unit recruitment-force relationship.
http://people.fmarion.edu/tbarbeau/physio_muscle_supplements.htm
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Week 7: Muscle and EMG Lab
Step 3: EMG-1 Exercise
The EMG has many practical applications. The electrical signal allows an individual to
visualize a muscle contraction and control the contraction. We will use EMG data to
assess motor activity, recruitment and fatigue while gripping an object.
Figure 5. EMG output for comparison between dominant and non-dominant arms
when asked to clench at different intensities.
Since you are performing this exercise
remotely we will provide you with the
output, but you should click video link
below to view a short (16 sec) video of
how the probes are positioned on the
forearm and how data are collected.
Click Link: https://www.youtube.com/watch?v=LI-s_UkXGko
Fig. 6: Snapshots of EMG measure
measurement using Biopac materials.
Table 1. Type your hypothesis for the stated EMG-1 activity that you will analyze.
Lab Activity
Hypothesis
[Enter Hypothesis 1 here…which arm to
you think will have the stronger signal?]
1. EMG I. State your hypothesis
regarding EMG signal of your
dominant vs. non-dominant arms.
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Week 7: Muscle and EMG Lab
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Week 7: Muscle and EMG Lab
Methods for EMG-1
1. Open BSL Analysis software
2. Click “Review sample data”
3. Click “Sample Lesson Data”
4. Select “Gail-L01”
5. Watch “EMG-01” Video posted to D2L Week 7 to
6. Using the methods shown in the video, use the Ibeam cursor to measure the EMG data contained
in Gail-L01 file. Your values should be used to
complete Table 2.
7. Using that same method and the I-beam cursor,
measure the Tonas between each cluster. Enter
the tonus measurements into Table 3.
Table 2 EMG measurements for online subject Gail-L01
Clench Cluster
Dominant
Non-dominant
CH 40 – Mean (mV-sec)
CH 40 – Mean (mV-sec)
1 – mild
0.059
0.075
2 – moderate
0.139
0.111
3 – strong
0.319
0.189
4 – strongest
0.417
0.337
Table 3 – Tonus measurements for Gail-L01.
Relax Cluster
Dominant
Non-dominant
CH 40 – Mean (mV-sec)
CH 40 – Mean (mV-sec)
1 – pre-mild
0.00456
0.00446
2 – pre-moderate
0.00371
0.00415
3 – pre-strong
0.00546
0.00555
4 – pre-strongest
0.00365
0.01120
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Week 7: Muscle and EMG Lab
Step 4: EMG-2 Exercise
Next, we are going to simulate the EMG
output for someone that is being asked to lift
different amount of weight using their
dominant and non-dominant arms.
Watch the video to see how the data were
collected using the BioPacs:
Tasks Performed in video
1. Lift weight (bicep curl) and hold for 2 sec.
2. Repeat cycles of weightlifting; add weight for each
cycle until the Subject is lifting the maximum weight.
3. Lift the maximum weight to 45 degrees and hold it until the onset of fatigue.
4. Repeat the sequence for the non-dominant arm.
Table 4. Type your hypothesis for the stated EMG activities that you will analyze.
Lab Activity
Hypothesis
1. EMG II. State your hypothesis
regarding the EMG signal while lifting
various weights.
[Enter Hypothesis 2 here…]
2. Fatigue. State your hypothesis
regarding fatigue time for your
dominant vs. non-dominant arms.
[Enter Hypothesis 3 here]
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Week 7: Muscle and EMG Lab
Methods for EMG-2: Lifting Weights
1. Open BSL Analysis software
2. Click “Review sample data”
3. Click “Sample Lesson Data”
4. Select “Gail-L02”
5. Watch “EMG-02” Video posted to D2L Week 7 to
6. Calculate the mechanical work in Table 5.
Work = weight x distance
7. Measure Force and Integrated Peak in Table 6
by following the instructions from Video EMG-02.
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Week 7: Muscle and EMG Lab
Table 5. Calculate work using formula on previous page.
Weight Lifted
Dominant Arm
Non-dominant Arm
Distance Lift
Mechanical
Work
(wt x distance)
Distance Lift
Mechanical
Work
(wt x distance)
1
1.36 kg
28 cm
kg*cm
28 cm
kg*cm
2
2.27 kg
28 cm
kg*cm
28 cm
kg*cm
3
4.54 kg
28 cm
kg*cm
28 cm
kg*cm
Table 6. Complete using sections 1 & 3 of Gail-L02 Data
Clench #
Assigned
Dominant
Non-dominant
Force
kg
Force at
peak (kg)
Integrated
EMG (mV)
Force at
peak (kg)
Integrated
EMG (mV)
CH 41
mean
CH 40
mean
CH 41
mean
CH 40
mean
1
1.36
8.89 kg
0.039 mV-s
7.14 kg
0.036 mV-s
2
2.27
17.57 kg
0.058 mV-s
17.34 kg
0.072 mV-s
3
4.56
27.00 kg
0.096 mV-s
27.28 kg
0.131 mV-s
4
6.28
35.66 kg
0.150 mV-s
31.21 kg
0.146 mV-s
Table 7. – Determine 50% of max clench abd time to fatigue (50% force reduction)
using sections 2 & 4 of Gail-L02 Data.
Max Clench Force (kg)
50% of Max Clench
Force (you calculate)
Time to Fatigue,
Ch 40 Delta T
Dominant
16.1 kg
74.5 seconds
Non-dominant
20.2 kg
24.3 seconds
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Week 7: Muscle and EMG Lab
Step 5: Questions and Discussion
EMG I
1. Compare the maximum (4th) EMG clusters in Table 2 between your dominant and
non-dominant arm.
a. Explain the source of the signals detected by the EMG electrodes. (HINT:
think about energy in the human body)
b. Is the clench strength the same? Why or why not?
2. Describe how motor unit recruitment changes the magnitude of the EMG signal.
3. Compare tonus between the dominant and non-dominant arm.
a. Describe the difference between the dominant and non-dominant arm in any
difference exists?
b. Why might a difference exist?
4. Did your results support your hypothesis for EMG I? Explain.
EMG II
5. Examine the strength between the dominant and non-dominant arm:
a. Which arm is stronger?
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Week 7: Muscle and EMG Lab
b. Using data from Table 6 & 7, explain the evidence for this conclusion.
6. When holding an object steady:
a. Does the number of motor units remain the same?
b. Are the same motor units used for the duration of holding the object?
7. Describe how fatigue affected your EMG recording. In other words, does it affect the
amplitude or timing of the recording? If so, how?
8. Jocelyn lifts 8 kg a distance of 25 cm and William lifts 10 kg a distance of 20 cm.
Who performs more work? Explain your answer. HINT: Work can be defined as
force times distance (W=F x d).
9. Did your results support your hypothesis for EMG II? Fatigue? Explain.
10. Come up with a follow-up experiment using EMG to further explore motor
recruitment and fatigue. (A 2-3 sentence answer is sufficient.)
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ECG (Biopac)
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