Lab 7

Approximate Time: 3 hours

EMG cable and Hand Dynamometer Setup

1. Locate the ROAM EMG and FT-220 hand dynamometer.
2. The FT-220 dynamometer should be already plug into Channel A2 input of the IXTA.

Figure 1: The EMG cable and hand dynamometer connected to an IXTA

3. Remove the ROAM EMG from the dock and place the electrodes as shown.

Figure 2: Placement of EMG electrodes on the forearm.

4. The subject should remove all jewelry from their wrists. For the first exercises in this lab, record EMGs and muscles forces from the subject’s dominant arm, the arm used most often.
5. Use an alcohol swab and scrub three regions on the inside of the subject’s dominant forearm where the electrodes will be placed. One area is near the wrist, the second is in the middle of the forearm, and the third area is about 2 inches from the elbow.
6. Remove the plastic disk from a disposable electrode and apply it to one of the scrubbed areas. Repeat for the other two areas.

Red (+) electrode to the right side of the ROAM

Roam near the wrist

Black (-) electrode to the left side of the room

Start the Software

1. Click on the Labscribe24 shortcut on the computer’s desktop/laptop to open the program.
2. On the Main window, pull down the Settings menu and select Load Group.
3. Locate the folder that contains the Complete Setting group, IPLMv7Complete.iwxgrp. Select this group and click Open.
4. Pull down the Settings menu again. Select Human Muscle. Select EMG-GripStrength-ROAM.
5. After a short time, LabScribe will appear on the computer screen as configured by the EMG-GripStrength-ROAM settings.

Procedure

1. The subject should sit quietly with his or her dominant forearm resting on the table top. Explain the procedure to the subject.

• The subject will squeeze his or her fist around the hand dynamometer five times, each contraction is two seconds long followed by two seconds of relaxation.
  • o Hold the dynamometer with the thumb out, just squeezing with the fingers. This uses only the forearm muscles and does not bring in the upper arm muscles.
• Each successive contraction should be approximately two, three, four times stronger than the first contraction; the final contraction should be full strength.

NOTE – If you max out the pressure and the signal flat lines – squeeze the bulb using ONLY your middle and ring fingers.

2. Type Grip Force-Dominant in the Mark box. Click the Record button to begin the recording; then click the mark button to mark the beginning of the recording. After the recording is marked, tell the subject to begin squeezing the hand dynamometer following the procedure outlined in the step above.

3. In the relaxation period after the last contraction, click the Stop button.

NOTE – If you max out the pressure and the signal flat lines – squeeze the bulb using ONLY your middle and ring fingers.

4. Click the AutoScale buttons for the EMG and Muscle Force Channels. The recordings should be similar to the image below.

Figure 3: The EMG (upper) and muscle force (lower) for four progressively stronger contractions displayed in the Main window.

Data Analysis

1. Use the Display Time icons to adjust the Display Time of the Main window to show the progressive muscle contractions on the Main window.
2. Click on the Analysis window icon in the toolbar.

Figure 4: The LabScribe Toolbar.

3. Look at the Function Table that is above the uppermost channel displayed in the Analysis window. The mathematical functions, Abs. Int., V2-V1, and T2-T1 should appear in this table.  The values for Abs, Int., V2-V1, and T2-T1 on each channel are seen in the table across the top margin of each channel.

4. Once the cursors are placed in the correct positions for measuring the absolute integrals under the muscle contraction and the corresponding EMG activity, the values of the integrals can be recorded in table 1.

5. Use the mouse to click on and drag the cursors to the beginning and end of the first muscle contraction. The values for Abs. Int. on the EMG and Muscle channels are the relative amount of the electrical activity causing the contraction and relative strength of the muscle, respectively.  Record the values on Table 1.

Figure 5: the EMG and muscle force recordings displayed in the Analysis window. The cursors are placed on the margins of the 2nd muscle contraction and the absolute integral function is used to measured the area under the EMG spikes and the area under the force recording.

6. Repeat Steps 3, 4, and 5 for the other muscle contractions recorded in this exercise.

7. Use a piece of string and a metric ruler to measure the circumference of the dominant forearm at approximately 3 centimeters below the elbow. Record this value on table 1.

Table 1

Procedure

1. The subject should sit quietly with his or her dominant forearm on the table top.
2. Explain the experimental procedure of this exercise to the subject:

• The subject will squeeze the bulb of the hand dynamometer as tightly and as long as possible in an attempt to fatigue the muscles of the forearm.
• As time passes, the subject’s muscle force will decrease, but at a rate that is dependent on the fitness of the subject.
• When the subject’s muscle strength drops to a level that is below half of the subject’s maximum muscle force at the beginning of the recording, the recording will be stopped. This could take as little as 20 seconds or as long as a couple of minutes.

3. Type Fatigue-Dominant in the Mark box. Click the Record button, followed by clicking the mark button. Record a baseline for ten seconds, then instruct the subject to squeeze and hold the hand dynamometer with as much force as possible.  Continue to record.
4. Click the AutoScale All button. The recording should be similar to the image below.

Figure 6: EMG and muscle force during muscle fatigue recording.

5. When the subject’s muscle strength decreases to a level that is below 50% of the maximum muscle strength that was recorded at the beginning of this exercise, instruct the subject to release the bulb. NOTE: DO NOT stop until the recording is 50% of the starting squeeze strength.
6. Click the Stop button to halt the recording.

Data Analysis

1. Use the Display Time icons to adjust the Display Time of the Main window to show the complete muscle fatigue recording on the Main window.
2. Data can be collected from the Main window or the Analysis window. If you choose to use the Analysis window, click on the Analysis window icon in the toolbar.
3. The mathematical functions, V2-V1 and T2-T1 should appear on screen. Values for V2-V1 and T2-T1 on each channel are seen in the table across the top margin of each channel, or to the right of each graph.
4. On the Muscle Force channel, use the mouse to click on and drag the cursors to specific points on the recording to measure the following:

• The maximum muscle force. To measure this force, place one cursor on the baseline before the muscle contraction and the second cursor on the peak muscle force near the beginning of the contraction.  The value for V2-V1 on the Muscle Force channel is the amplitude.
• The half-max muscle force. Divide the maximum force by 2. Note this value.
• The half-max fatigue time, which is the time it takes the muscle force to decrease to 50% of the maximum during the fatigue experiment. Keep one cursor on the peak of the muscle force.  Move the second cursor to the right of the peak muscle force until the absolute value for V2-V1, seen on the Muscle Force channel, is equal to the half-max muscle force.

Figure 7: The EMG (upper) and muscle force (lower) during a prolonged muscle contraction displayed in the Analysis window. The cursors are placed on the muscle force channel to measure the half-max fatigue time.

Procedure

1. Follow the same directions used in Exercise 1 to record data from the subject’s non-dominant forearm.

Data Analysis

1. Analyze the data from the subject’s non dominant forearm as it was done in Exercise 1.
2. Record the values for the parameters that were measured in Table 2.
3. Use a piece of string and metric ruler to measure the circumference of the non-dominant forearm.

Table 2

Procedure

1. Follow the same directions used in Exercise 2 to record fatigue data from the subject’s non-dominant forearm.

Data Analysis

1. Analyze the fatigue data from the subject’s non-dominant forearm as it was done in Exercise 2.