BIO 240 – Week 6 Workshee t
Names______________________________
GRIP STRENGTH AND ELECTROMYOGRAM (EMG) ACTIVITY, part 1
The equipment should be assembled when you come into the lab. Working in pairs, choose the
Subject and the Experimenter. Both of you should read the lab and be sure that you understand
what you are doing before you do it.
Start the Software
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Double click the LabScribe icon on the desktop.
Click the Settings menu.
Select Load Group.
From the dialog box, select IPLMv4.iwxgrp. Click Load.
Click on the Settings menu again.
Select EMG-GripStrength. This is found under human muscle. In a second or two, the
lab manual itself will spear. X out and two or three windows will appear on the screen
(EMG, EMG Integral, and Force).
Calibrating the Hand Dynamometer
o Collect 4-5 textbooks and weigh them in kilograms on the scale. __________kg
o (1 kilogram = 2.2 lbs)
o Record the weight of the stack in kilograms in the Journal. To open the Journal click on
the Journal button in the LabScribe toolbar.
o Lay the hand dynamometer on the bench top.
o In the upper right hand corner of the screen, click Start and record for 10 seconds (watch
the lower right hand of the screen to follow the clock).
o After 10 seconds, place the stack of books on the dynamometer.
o Measure for 10 more seconds, then click Stop at the upper right hand side of the screen.
o Click each of the Autoscale words found associated with each window on the screen.
o Use the Double Display Time icons (3rd and 4th from the left of the Toolbar at the top of
the screen) to adjust the time display on the screen so you can see the time before and the
time after the books were placed on the dynamometer.
The button to the left (big mountain) changes the display time to 5 seconds.
The button to the right (small mountains) displays 20 seconds. (This is probably
the one to use.)
o Click the 2-Cursor icon (2nd from the left on the Toolbar) and two blue vertical lines will
appear over the screens. In the third window (force), place the left-hand cursor on the flat
line before the upward deflection (no books) and place the right hand cursor on the flat
line after the upward deflection. (after placement of books) (Do this by placing the cursor
over the line, holding down the left mouse button, and dragging it where you want it.)
o Right click in the data display area of the 3rd window (force).
Select Units and Simple from the submenu to open the Simple Units Conversion
Dialogue Window
Put check marks in the boxes next to Apply Units to new data and Apply Units to
all blocks. Click on the units off button to remove any prior units conversion from
this channel.
For Value at Cursor 1, type 0 in the box on the right
For Value at Cursor 2, type the mass of the books (from _____kg above)
For Name, type kg, and then click OK.
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EXERCISE 1: EMG INTENSITY AND FORCE
Procedure
o The Subject should attach the three color-coded electrodes on her dominant
forearm as shown in Figure HM-1-4, and then rest her arm on the tabletop.
o Sitting quietly, the Subject will clench and release her fist around the
dynamometer 4 times. Each clench is for 2 seconds, followed by 2 seconds of
rest. Each clench should be stronger than the one before it. The 4th clench should
be full strength.
o Click the Start button to begin recording. Immediately type “Increasing
Clenches” in the comment line to the right of the Mark button. Press the Enter
key on the keyboard. The Subject should begin the hand clenches. After the 4th
clench, press Stop.
o Click Autoscale for all 3 channels.
Top graph = actual recorded EMG
Middle graph = EMG integral = mathematically transformed EMG
Lower graph = force produced by the hand clench
o Click File (from the upper menu bar), than Save As, Student Data, Name, Save
Data Analysis
o If necessary, use the Display Time icons to get all 4 clenches on the screen.
o Click the 2-Cursor icon and bracket the 4 clenches (flat to the left of the first
clench and the flat line to the right of the fourth clench).
o Click the Analysis icon (11th from the right on the toolbar).
o Look at the Function Table that is above the uppermost channel displayed in the
Analysis window. The mathematical functions, Abs. Area, V2-V1, and T2-T1
should appear in this table. The values for Abs. Area, V2-V1, and T2-T1 on each
channel are seen in the table across the top margin of each channel.
o Place the 2 cursors on either side of the 1st raw EMG cluster. Record Absolute
Area of EMG Activity and Absolute Area under Force Curve in the table provided
below.
o Repeat all of the above for the 2nd, 3rd, and 4th hand clenches.
Hand
clenches
Lowest
Higher 1
Higher 2
Highest
Absolute Area of EMG
Activity
Absolute Area under Force
Curve
Do the following:
1.
On the graph provided below, plot the absolute area under Force for the muscle
clenches as a function of the absolute area under the EMG for each muscle
clench.
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2.
Is there a linear relationship between the absolute area under EMG signals and the
absolute area under the muscle contraction force?
This should be a fairly linear graph with an up-slope curve. The EMG should be
less when grip strength is low, and higher as the grip increases.
3.
Does the amplitude of the EMG signal and the force of contraction increase
because a finite number of fibers are firing more often, or because more fibers are
recruited to fire, or a combination of the two? Explain your thinking.
It is more of a combination of the two cases. As recruitment of muscle fibers
increases, the amplitude of the EMG signal will increase. Muscle fibers can fire
more often only up to a point and then more muscle fibers need to be recruited.
Thus, you will see an increase in the EMG amplitude.
EXERCISE 2: EMG INTENSITY AND FATIGUE IN DOMINANT ARM
Procedure
o Click the Main icon on the toolbar (12th from the left) to prepare the screen for the
next set of data collection.
o The Subject should sit quietly with the dominant arm on the bench top and still
attached to the electrodes.
o Click the Start button and collect baseline data for a few seconds.
o Click the AutoScale buttons from the EMG and Muscle Force Channels.
o The Subject should then squeeze the dynamometer as hard as possible for as long
as possible. When the Force measurement (2nd panel) falls to 50% of the original
force generated, the Subject can stop. Follow this value by first looking at the
initial maximum force of contraction, and then follow the force at the top right of
the 2nd panel. Click the Stop button.
o Click Save from the File menu.
o Measure the circumference of the Subject’s dominant forearm at its widest part.
__________cm
Data analysis
o Adjust the screen time of the Main window to display the complete record of this
experiment on the same screen (Display Time icons).
o The complete recording can also be selected by:
Placing one cursor on the relaxation period just before the contraction and
the other cursor on the relaxation period just after the subject releases the
hand dynamometer; and clicking Zoom between Cursors.
o Click the Analysis icon.
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o
Look at the Function Table that is above the uppermost channel displayed in the
Analysis window. The mathematical functions, Abs. Area, V2-V1, and T2-T1
should appear in this table. The values for Abs. Area, V2-V1, and T2-T1 on each
channel are seen in the table across the top margin of each channel.
o Click the 2-Cursor icon. On the Muscle Force channel place one cursor on the
baseline before muscle contraction and the second cursor on the peak muscle
force near the beginning of the contraction. V2-V1 is the difference in amplitude
(kilograms of force). Record this data. _________
o Divide the maximum clench force by 2=_________ = half-maximum clench force
o Determine the time it took the Subject’s forearm to fatigue to half its strength.
Put one cursor on the peak of the clench force. Move the other cursor to the right
of the peak muscle force until the V2-V1 absolute value is equal to the value you
determined above as half-maximum clench force. The value for T2-T1 is the time
it took the subject’s forearm flexor muscles to fatigue to half of their strength.
Record this value __________sec
Answer this question – Look at your force graph and the EMG Integral graph (click the
Main icon). Why does the amplitude of the EMG Integral get larger even though
the force of contraction is dropping? What is happening? What is the nervous
system telling the muscle fibers? More neurons are firing so there is additional
electrical activity in the muscle. However, the muscle is fatigued.
EXERCISE 3: EMG INTENSITY , FORCE, AND FATIGUE IN THE NON-DOMINANT ARM
Procedure
o Move the electrodes from the dominant forearm to the non-dominant forearm of
the Subject. If they have lost their stickiness, get another set.
o Follow the same procedure as above. With the Subject resting quietly, click the
Start button to gain some baseline data. The Subject should then clench as hard
as possible. Once the force of contraction has fallen to 50% of maximum, the
Subject can stop the contraction. Press the Stop button, and then analyze the data.
o Circumference of non-dominant forearm at its widest point __________
Data analysis
o Adjust the screen time of the Main window to display the complete record of this
experiment on the same screen (Display Time icons).
o The complete recording can also be selected by:
Placing one cursor on the relaxation period just before the contraction and
the other cursor on the relaxation period just after the subject releases the
hand dynamometer; and clicking Zoom between Cursors.
o Click the Analysis icon.
o Look at the Function Table that is above the uppermost channel displayed in the
Analysis window. The mathematical functions, Abs. Area, V2-V1, and T2-T1
should appear in this table. The values for Abs. Area, V2-V1, and T2-T1 on each
channel are seen in the table across the top margin of each channel.
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o Click the 2-Cursor icon. On the Muscle Force channel place one cursor on the
baseline before muscle contraction and the second cursor on the peak muscle
force near the beginning of the contraction. V2-V1 is the difference in amplitude
(kilograms of force). Record this data. _________
o Divide the maximum clench force by 2=_________ = half-maximum clench force
o Determine the time it took the Subject’s forearm to fatigue to half its strength.
Put one cursor on the peak of the clench force. Move the other cursor to the right
of the peak muscle force until the V2-V1 absolute value is equal to the value you
determined above as half-maximum clench force. The value for T2-T1 is the time
it took the subject’s forearm flexor muscles to fatigue to half of their strength.
Record this value __________sec
Do the following:
1.
Calculate the percentage difference in maximum grip strength for the two
forearms.
Dominant forearm maximum strength
= __________
Non-dominant forearm maximum strength = __________
Percentage difference
= __________
2.
Calculate the percentage difference in fatigue times for the two forearms
Dominant forearm
Non-dominant forearm
Percent difference
3.
= __________
= __________
= __________
Calculate the difference in circumference between the two forearms
Dominant forearm
Non-dominant forearm
Percent difference
= __________
= __________
= __________
Answer the following questions:
1.
Is there a significant difference in maximal strength generated between the two
forearms? If there is an obviously dominant forearm, then you should see a
difference in the maximum forces generated by the two arms. If a student
exercises both arms equally, there may not be a noticeable difference.
2.
Is there a significant difference in time to fatigue (50% of maximal strength)
between the two forearms? The non-dominant forearm should fatigue faster than
the dominant arm if there is an obvious strength difference between the two arms.
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3.
If there is a difference in the circumferences of the two forearms, is it caused by a
difference in the number of muscle fibers or the diameter of each muscle fiber in
the forearm? Explain. There may or may not be a difference in the circumference
between forearms. You may see a larger difference in circumference in a subject
that does not do regular upper body exercise. However if there is a difference,
this is likely due to increasing the diameter of each muscle fiber in the dominant
arm rather than increasing the number of muscle fibers.
4.
Does this have anything to do with the time to fatigue? Explain?
Yes, the dominant arm with larger diameter fibers will likely have more
mitochondria and more myofibrils so therefore it will take the fibers longer to
fatigue. The dominant arm may also be more conditioned to responding more
quickly.
EMGS IN ANTAGONISTIC MUSCLES, part 2
EXERCISE 4: INTEGRATION OF MOTOR ACTIVITY
Equipment Set-Up
o Plug in the brown and white electrodes.
o Go to the Settings menu and select EMG-Antagonistic-Muscles. The flexor
muscles will appear on channel 1 and the extensor muscles will appear on channel
2.
o Attach the leads according to figure HM-2-4. Be sure that the white and brown
leads are on the back of the forearm, over the extensor muscles.
Procedure
o It is important that the Subject hold their arm out from the body, palm facing
upward and not resting on the tabletop.
o Click Start to begin recording. Type “Neutral” in the Mark line and press Enter
on the keyboard. The Subject should slowly flex his/her hand with hand open and
hold for 4 seconds and then return to neutral position. The subject should then
move the hand downward (extension) and hold for 4 seconds before returning to
neutral position.
o Note: When the subject’s hand is in the neutral position, type Flexion in the Mark
Box. When the subject flexes his or her hand, click on the Mark button or press
the Enter Key on the keyboard. When the subject’s hand is in the flexed position,
type Neutral in the Mark box. When the subject returns his or her hand to the
neutral position , click on the Mark button or Enter Key on the keyboard. When
the subject’s hand is in the neutral position, type extension in the Mark box.
When the subject extends his or her hand, click on the Mark button or click Enter
Key on keyboard.
o Click Stop after 3-4 cycles.
o Repeat the experiment, but have the Subject form a fist.
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o Review your data by using the slider bar at the bottom of the screen.
o Click on Analysis.
o Look at the Function Table that is above the uppermost channel displayed in the
Analysis window. The mathematical functions, Abs. Area, Max-Min, and T2-T1
should appear in this table. The values for Abs. Area, Max-Min, and T2-T1 on
both the anterior and posterior channels are seen in the table across the top margin
of each channel.
o The values for Abs. Area, Max-Min, and T2-T1 are the relative amounts of the
EMG activity, the differences between maximum and minimum EMG amplitudes,
and the durations of the EMG burst in each muscle group.
o Using the 2 Cursor method to drag the cursors to the onset and offset of the EMG
burst during all flexions for both the anterior and posterior muscle groups.
o Write down the Abs. Area, Max-Min, and T2-T1 for each muscle group during
flexion and calculate the average Abs. Area, Max-Min and T2-T1 for each muscle
group.
o Do the same for each muscle group during all extensions.
Forearm action
Anterior Muscles
Abs. Area / Max-Min/ T2-T1
Posterior Muscles
Abs. Area / Max-Min/ T2-T1
Flexion,
Hand Open
Extension,
Hand Open
Flexion,
Hand Closed
Extension,
Hand Closed
Answer the following questions:
1.
Where does myogram activity most occur during extension? During flexion?
The posterior muscle group of the forearm causes extension of the wrist.
The anterior muscle group in the forearm causes flexion of the wrist.
2.
Does flexion or extension of the fingers affect the strength of EMG activity in
either group of muscles? Both flexion and extension of the fingers will have an affect on
the strength of EMG activity. Flexion of fingers will increase the EMG amplitude during
wrist flexion, while extension of fingers will decrease it. The opposite is true of wrist
extension.
3.
What is the relationship between motor neuron activity, EMGs, muscle
performance, and work? There is a direct relationship between all of these
factors. If you increase motor neuron activity, you should see an increase in
EMGs, an increase in muscle performance and an increase in work.
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