Muscle 2: Muscles in Opposition

Antagonistic Muscles in Your Forearm

Aim

To study the EMG activity in muscles that work in opposition to each other to flex or extend the hand.

Procedure

READ THESE DIRECTION FIRST:

• Before the recording begins, hold your non-dominant arm out in front of your body with the palm facing upward. This position is defined as the neutral position.
• Keep your hand open during the recording.
• Move your hand upward (flexion) from the neutral position as far as possible and hold it in this position for four seconds.

• Return your hand to the neutral position for four seconds.
• Move your hand downward (extension) as far as possible and hold it in this position for four seconds. Timing is important.
• Return your hand to the neutral position for at least two seconds.
• Repeat this cycle of flexion and extension two more times.

1. Before starting the recording, type "Neutral" in the Mark box to the right of the Mark button. Put your arm and hand in the neutral position.
2. Click Record. Click the Mark button.
3. While your hand is in the neutral position, type "Flexion" in the Mark box. When the your flex your hand click the Mark button to label the recording.
4. While your hand is in the flexed position, type "Neutral" in the Mark box. When you return your hand to the neutral position, click the Mark button.
5. While your hand is in the neutral position, type "Extension" in the Mark box. When you extends your hand, click the Mark button.
6. Repeat Steps 1 through 6 two more times while the your palm is open.
7. Click AutoScale All to see all the activity clearly.
8. Click File ---> Save As, name the file "MuscleOppositon", and save your data to your LabScribe Data folder on your Desktop.
9. Repeat Steps 1 through 7 three times while making a tight fist.
10. When the last cycle is completed, click Stop.
11. Click on the Save.

Data Analysis

1. Click the "two mountain" icon to double the display time to show the whole recording on the screen while the subject’s palm was flat. You may have to click the mountains a couple of times.
2. Click the Analysis Window icon on the toolbar.

3. Click and drag the cursors to either side of the first EMG (muscle activity) burst. Abs. Int is the relative amount of the electrical activity causing the muscle activity for both the flexors and extensors. Record the values in the table below.
4. Repeat Step 3 for the other flex and extend muscle contractions.
5. Select Save from the File menu.

Put all your data in a data table or in the Journal so you can refer back to it. You can open and close the Journal using the "Notebook" icon.

Antagonistic Muscles Doing Work

Aim

To study the EMG activity in muscles that lift weight by flexion or by extension.

Procedure

1. Use the same experimental setup used in Exercise 1.
2. Rest your forearm on a flat surface with your palm up.
3. Hold a 2-3 kg weight in your palm. If you do not have a weight, you can use a 1 liter bottle of soda or something equivalent.
4. Click Record. Record the EMG activity from the muscles of the forearm as you lift the weight by the flexion. Raise and hold the weight up for four seconds and then return the weight to the table top (Neutral) for four seconds. Repeat this cycle two more times.
5. Click Stop and save your data.

6. Now, rest your forearm on a flat surface with your hand hanging over the edge so your palm is down.
7. Hold the same weight as before (2-3kg).
8. Click Record. Record the EMG activity from the muscles of the forearm as you lift the weight by extension. Raise and hold the weight up for four seconds and then return the weight to the table top for four seconds. Repeat this cycle two more times.
9. Click Stop and save the data.

Data Analysis

1. Repeat the same procedure from Exercise 1 to analyze the data.
2. Click the "two mountain" icon to double the display time to show the whole recording on the screen while the subject’s palm was flat. You may have to click the mountains a couple of times.
3. Click the Analysis Window icon on the toolbar.
4. Click and drag the cursors to either side of the first EMG (muscle activity) burst. Abs. Int is the relative amount of the electrical activity causing the muscle activity for both the flexors and extensors.
5. Repeat Step 3 for all the other flex and extend muscle contractions.
6. Select Save from the File menu.

Remember to put your data into a data table or into the Journal using the "Notebook" icon.

Answer the following:

Exercise 1

1. Which muscles, anterior or posterior, had the most EMG activity during flexion?
2. Which muscles, anterior or posterior, had the most EMG activity during extension?
3. Does extension or flexion of the fingers (open hand or making a fist) affect the strength of EMG activity in either group of muscles?

Exercise 2

1. Does the strength of the EMG activity in the muscles of the anterior forearm differ between flexion with a weight and without a weight?
2. Does the strength of the EMG activity in the muscles of the posterior forearm differ between extension with a weight and without a weight?
3. Why do you think there is a difference in the amount of EMG when the subject does not have a weight vs when they do have a weight? You may need to use your text or look up more information.