Introduction
In this laboratory, you will explore the electrical activity of skeletal muscle by recording an
electromyogram (EMG) from a volunteer. You will examine the EMG of both voluntary and evoked
muscle action, and measure nerve conduction velocity.
Learning Objectives
By the end of today's laboratory you will be able to:
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Record EMG during voluntary muscle contractions, and investigate how contractile force changes
with increasing demand
Examine the activity of antagonist muscles and the phenomenon of coactivation
Record Grip Force
Examine the activity of muscle related to Grip Force
Procedure
Electrode attachment:
Remove any watch, jewelry, etc. from your wrists.
Plug the five-lead Bio Amp cable into the Bio Amp socket on the PowerLab unit.
Plug the five color-coded lead wires into the Bio Amp cable, as shown.
Firmly attach the dry earth strap around your palm or wrist. The fuzzy side of the dry earth strap
needs to make full contact with the skin. Attach the green lead wire to the earth strap. If the dry
earth strap has a single connector lead wire it should be inserted onto the pin nearest the Earth
label.
5. If alcohol swabs are available, firmly swab the skin with them in each area where electrodes will
be placed. Lightly mark two small crosses on the skin overlying the biceps muscle, in the position
for the biceps recording electrodes, as shown. The crosses should be 2-5 cm apart and aligned
with the long axis of the arm. Lightly abrade the skin at these areas with abrasive gel or a pad.
This is an essential step as it decreases the electrical resistance of the outer layer of skin and
ensures good electrical contact.
1.
2.
3.
4.
6. Prepare the skin over the triceps for attaching the electrodes as outlined in step 5 for the biceps.
The position for the triceps recording electrodes is shown in the figure.
7. Prepare the disposable ECG electrodes by removing the backing film. Place the electrodes onto
the skin over the crosses so they adhere well.
8. Plug the four shielded lead wires into the Bio Amp cable ports for positive and negative, CH1 and
CH2.
9. Snap the lead wires from CH1 on the Bio Amp cable onto the electrodes on the subject's
biceps.Snap the lead wires from CH2 on the Bio Amp cable onto the electrodes on the subject's
triceps. It does not matter which is positive and which is negative.
10. Check that all four electrodes and the dry earth strap are properly connected to the volunteer and
the Bio Amp cable before proceeding.
11. Make sure the PowerLab is connected and turned on.
Exercise 1
You will record electrical activity during voluntary muscle contractions, and investigate how it
changes with increasing demand.
The two lower channels in the LabTutor panel show raw activity; the two upper channels display
integrated activity, calculated from the raw signal. Integrated activity is commonly used in the
assessment of muscle function because it is easier to quantitate.
Procedure
During the experiment, use Autoscale whenever necessary to ensure you can see all the data
recorded.
1. Sit in a relaxed position, with your elbow unsupported and bent to 90° with the palm facing
upwards.
2. Click Start to resume recording.
3. Have someone hand you the empty weight cradle which weighs 500 grams. Enter the
comment "500 grams",
4. Keep the object in your hand for 10 seconds and your elbow at 90° to record the change in
the EMG.
5. Add a weight (1 kg) to the cradle and keep your elbow at 90° for 10 seconds. Enter the
comment "1.5 kg"
6. Repeat the process each time adding another 1kg weight and a new comment.
7. Press Stop.
Raw Data vs Integral Data
1. Scroll through the recorded data and note the changes in activity in the raw biceps channel
(Biceps). Note also that placing weights on the hand gives rise to little or no activity in the
triceps muscle.
2. Choose a small part of the "Biceps" activity and examine it in more detail by setting the
Horizontal compression to 1:1 and clicking Autoscale. Note that the raw EMG signal is
composed of many partly-overlapping spikes.
3. Note the relationship between the raw trace (Biceps) and integrated trace (Int. Biceps). The
height of the integrated trace reflects the overall activity of the raw EMG signal, and gives a
simpler view of the muscle's electrical activity. The integrated trace (Int. Biceps) is the
mathematical integral of the absolute value of the raw EMG signal. This represents the
filtered signal (clean signal) that facilitates analysis.
Analysis
1. Scroll through the recorded data and note the changes in activity in the raw biceps channel
(Biceps). Note also that placing weights on the hand gives rise to little or no activity in the
triceps muscle.
2. Choose a small part of the "Biceps" activity and examine it in more detail by setting the
Horizontal compression to 1:1 and clicking Autoscale. Note that the raw EMG signal is
composed of many partly-overlapping spikes.
3. Note the relationship between the raw trace (Biceps) and integrated trace (Int. Biceps). The
height of the integrated trace reflects the overall activity of the raw EMG signal, and gives a
simpler view of the muscle's electrical activity.
4. Use the Waveform Cursor to select the Avg Biceps Channel. Click on the Channel 5
seconds after you added the weight.
5. Use the Value panel to record in the table the amplitude of the Avewrage integrated Biceps
trace as weights were added.
Exercise 2
You will examine the activity of antagonist muscles and the phenomenon of coactivation.
Procedure
1.
2.
3.
4.
5.
Sit in a relaxed position, with your elbow bent to 90° with the palm facing upwards.
Place the cradle with all the weights in your and keep the elbow angle at 90°.
Click Start.
Keep the weight at 90° for as long as possible without doing harm to yourself
Click Stop.
Analysis
1. Scroll through the recorded data and observe the EMG traces for both the biceps and
triceps.
2. Note the alternation of activity in the biceps and triceps.
3. Use the X-axis to determine how long you were able to hold the weight
4. Divide the time you were able to hold the weight by 10. Use this value to as the interval at
which you will do your measurements
5. Start at the beginning and measure at each interval and insert into the table the integrated
EMG peaks for biceps and triceps during the time you held the weight. You do this using
the two Value panels.
Exercise 3
You will record electrical activity during voluntary muscle exercises, and investigate how Bicep and
Tricep EMG is affected.
The two lower channels in the LabTutor panel show raw activity; the two upper channels display
integrated activity, calculated from the raw signal. Integrated activity is commonly used in the
assessment of muscle function because it is easier to quantitate.
Procedure
During the experiment, use Autoscale whenever necessary to ensure you can see all the data
recorded.
1. Once again sit in a relaxed position, with your elbow unsupported and bent to 90° with the
palm facing upwards.
2. Click Start to resume recording.
3. Have someone hand you the weight cradle with all the weights. Enter the comment "Activity
1",
4. Keep your elbow at 90° for 5 seconds
5. Keep the object in your hand and your elbow at 90°
6. Add the comment "Activity 2"
7. Straighten your elbow to 180° slowly so that it takes 5 seconds to completely straighten.
The 180° represents a straight arm alongside the body.
8. Keep the object in your hand and your elbow at 180°
9. Add the comment "Activity 3"
10. Lift the weight slowly from 180° to 90° so that it takes 5 seconds to reach 90°
11. Press Stop.
Analysis of Activity 1
1. Scroll through the recorded data and observe the EMG traces for both the biceps and
triceps of Activity 1.
2. Note the alternation of activity in the biceps and triceps.
3. Start at the beginning of Activity 1 and measure 5 one second intervals and insert into the
table the integrated EMG peaks for biceps and triceps during the time you held the weight.
You do this using the two Value panels.
Analysis of Activity 2
1. Scroll through the recorded data and observe the EMG traces for both the biceps and
triceps of Activity 2.
2. Note the alternation of activity in the biceps and triceps.
3. Start at the beginning of Activity 2 and measure 5 one second intervals and insert into the
table the integrated EMG peaks for biceps and triceps during the time you held the weight.
You do this using the two Value panels
Analysis of Activity 3
1. Scroll through the recorded data and observe the EMG traces for both the biceps and
triceps of Activity 3.
2. Note the alternation of activity in the biceps and triceps.
3. Start at the beginning of Activity 3 and measure 5 one second intervals and insert into the
table the integrated EMG peaks for biceps and triceps during the time you held the weight.
You do this using the two Value panels.
Procedure
Electrode attachment:
Remove any watch, jewelry, etc. from your wrists.
Plug the five-lead Bio Amp cable into the Bio Amp socket on the PowerLab unit.
Plug the three color-coded lead wires into the Bio Amp cable, as shown.
Firmly attach the dry earth strap around your palm or wrist. The fuzzy side of the dry earth strap
needs to make full contact with the skin. Attach the green lead wire to the earth strap. If the dry
earth strap has a single connector lead wire it should be inserted onto the pin nearest the Earth
label.
5. If alcohol swabs are available, firmly swab the skin with them in each area where electrodes will
be placed. Lightly abrade the skin at these areas with abrasive gel or a pad.
This is an essential step as it decreases the electrical resistance of the outer layer of skin and
ensures good electrical contact.
1.
2.
3.
4.
6. The position of the recording electrodes should be placed on the flexor digitorum superficialis as
shown in the figure.
7. Prepare the disposable ECG electrodes by removing the backing film. Place the electrodes onto
the skin with the connecting pins on the electrodes 2 cm apart. The electrodes might have to
overlap to achieve this.
8. Plug the two shielded lead wires into the Bio Amp cable ports for positive and negative.
9. Snap the lead wires on the Bio Amp cable onto the electrodes on the subject's arm.
10. Check that the two electrodes and the dry earth strap are properly connected to the volunteer and
the Bio Amp cable before proceeding.
11. Connect the plug of the grip force transducer to Input 1.
12. Make sure the PowerLab is connected and turned on.
Exercise 4
You will record grip force and electrical activity during forearm muscle contractions, and
investigate how it changes with increasing demand.
The top window showS the Grip Force of the Volunteer.
The bottom window shows the EMG of the contracting muscles
Procedure
During the experiment, use Autoscale whenever necessary to ensure you can see all the data
recorded.
1. Sit in a relaxed position, with your elbow bent to 90° with the dynamometer in the hand of
the arm connected to the EMG electrodes.
2. Click Start.
3. Add the comment "25%", and grip the dynamometer to 25% of your grip strength by
observing the Grip trace and keep gripping at 25% for 5 seconds.
4. Click Stop.
5. Once again sit in a relaxed position, with your elbow unsupported and bent to 90° with the
dynamometer in hand.
6. Click Start to resume recording.
7. Repeat steps 2-4 for 50%, 75% and 100% to give a series of increasing grip strengths,
adding a comment each time.
Analysis
1. Scroll through the recorded data and note the changes in activity in the Forearm EMG
channel. Note also that altering Grip Strength affects Forearm EMG.
2. Choose a small part of the "Forearm EMG" activity and examine it in more detail by setting
the Horizontal compression to 1:1 and clicking Autoscale. Note that the EMG signal is
composed of many partly-overlapping spikes.
3. Use the Waveform Cursor and Value panel to record in the table the amplitude of the
Forearm EMG trace as Grip Strength was increased. The height of the trace correlates with
the force produced by the muscle.