Download Electromyography in Biological Psychology Lab | PSY 230 and more Lab Reports Biological Psychology in PDF only on Docsity!
ELECTROMYOGRAPHY (EMG) Laboratory
Motor unit recruitment & Fatigue
Comparison of dominant versus non-dominant arm using a within subject repeated
measures statistical analysis
Written by:
Richard Pflanzer, Ph.D.
Associate Professor Indiana University School of Medicine Purdue University School of Science
J.C. Uyehara, Ph.D.
Biologist BIOPAC Systems, Inc.
William McMullen
Vice President BIOPAC Systems, Inc.
David Pittman, Ph.D.
Associate Professor Wofford College Department of Psychology
Manual Revision PL3.7.0 M3.0.6 080706 Modified by David Pittman 030107
BIOPAC Systems, Inc.
42 Aero Camino, Goleta, CA 93117 (805) 685-0066, Fax (805) 685- Email: info@biopac.com Web: http://www.biopac.com
Page 2 http://webs.wofford.edu/pittmandw/psy230/lab.htm EMG Laboratory
I. INTRODUCTION
Mechanical work , in the physical sense, refers to the application of a force that results in the movement of an object. Skeletal muscle performs mechanical work when the muscle contracts and an object is moved, as in lifting a weight. To lift a weight, your muscles must exert a force great enough to overcome the weight. If you exert less force, then the weight does not move (Fig. 2.1). Physiologically, skeletal muscle is stimulated to contract when the brain or spinal cord activates motor units of the muscle. Motor units are defined as a motoneuron and all of the muscle fibers that the motoneuron innervates. An action potential (AP) in a human motoneuron always causes an action potential in all of the muscle fibers of the motor unit. As a matter of fact, humans generally do not send just one AP at a time down a motoneuron. Instead, a train of APs is sent — enough to induce tetany (the sustained fusion of individual muscle twitches) in the muscle fibers of the motor unit. [A discussion of motor units and their control was presented in Lesson 1.] Most human skeletal muscles are composed of hundreds of motor units (Fig. 2.2). When a skeletal muscle is called on to perform mechanical work, the number of motor units in the muscle activated by the brain is proportional to the amount of work to be done by the muscle; the greater the amount of work to be done, the greater the number of motor units activated. Thus, more motor units are simultaneously active when a skeletal muscle lifts 20 kilograms than when the same muscle lifts 5 kilograms.
Fig. 2.2 Example of Motor Units The brain determines the number of active motor units required for a muscle to perform a given task by utilizing sensory information from stretch receptors in the muscle and associated tendons and joint capsules. For example, when lifting a bucket of water from the ground, the brain first activates several motor units in the requisite skeletal muscles. If sensory information returning from the muscles indicates the muscles are contracting but not developing adequate power to lift the bucket, the brain activates additional motor units until the sensory information indicates the bucket is being lifted. The sequential activation of motor units to perform a designated task is called motor unit recruitment. Once you have lifted a light object, the brain recruits approximately the same number of motor units to keep the object up, but cycles between different motor units. The muscle fibers consume stored energy available in the muscle, and generate a force by contracting. As the muscle fibers deplete this fuel source, more energy must be created in order to continue contracting. By recruiting different motor units, motor units can relax and replenish their fuel sources.
Fig. 2.
Page 4 http://webs.wofford.edu/pittmandw/psy230/lab.htm EMG Laboratory
IV. EXPERIMENTAL METHODS
A. SET UP – THE LABORATORY EXPERIMENT WILL BE CONDUCTED IN RMSC 228B
(DAVIS RIG ROOM) OR RMSC 230 ( HISTOLOGY ROOM) IN THE MAIN
NEUROSCIENCE LABORATORY
FAST TRACK SET UP Detailed Explanation
- Turn computer ON. Login: PSYNEURO / Password: Psychology
- Make sure that the BIOPAC MP30 unit is OFF.
- Plug the equipment in as follows:
Hand Dynamometer (SS25LA or SS25L) — CH 1 Electrode lead Set (SS2L) — CH 3 Headphones (OUT1) — back of unit
Headphones (BIOPAC OUT1) plug into back of MP35/30 unit
Lead Set BIOPAC SS2L plugs into CHannel 3 Hand Dynamometer (BIOPAC SS25LA or SS25L shown ) plugs Fig. 2.3 Equipment Setup
- Turn ON the BIOPAC MP30 unit.
- Remove any jewelry or watches from your wrists. Attach three electrodes to each forearm (Fig. 2.4).
- Attach the electrode lead set (SS2L) to the Subject’s dominant forearm, following the color code (Fig. 2.4).
IMPORTANT Make sure the electrode lead colors match Fig. 2.4.
Set Up continues…
Attach three electrodes to each forearm as shown in Fig. 2.4.
For optimal electrode adhesion, place electrodes on
the skin at least 5 minutes before the start of Calibration. Attach the lead set (SS2L) to the Subject’s dominant forearm (Fig. 2.4) for recording Segments 1 and 2 (forearm 1).
If the subject is right-handed, the right forearm is generally dominant; if
the subject is left-handed, the left forearm is generally dominant.
You will switch the lead set to the Subject’s non-dominant arm for
recording Segments 3 and 4 (Forearm 2).
White Lead (-)
Black Lead (Ground)
Red Lead (+)
Fig. 2.4 Electrode Placement & Lead Attachment
EMG Laboratory http://webs.wofford.edu/pittmandw/psy230/lab.htm Page 5
The electrode lead cables are each a different color and
each must be attached to a specific electrode position, as shown in Fig. 2.4.
The pinch connectors work like a small clothespin and
will only latch onto the nipple of the electrode from one side of the connector.
- Start the BIOPAC Student Lab Program. There is a shortcut for the Student Lab program on the desktop and under the Programs Æ Biopac menu.
- Choose lesson “ L02-EMG-2” and click OK.
- Type in a unique filename. (username such as PittmanDW) This filename will be used to create a folder to store your data. I suggest that you use your username: Last Name, First & Middle Initial (for example: PittmanDW)
- Click OK. This ends the set-up procedure.
END OF SET UP
EMG Laboratory http://webs.wofford.edu/pittmandw/psy230/lab.htm Page 7
C. RECORDING LESSON DATA
FAST TRACK RECORDING Detailed Explanation of Steps for Recording Lesson Data
- Prepare for the recording. In order to work efficiently, read this entire section so you will know what to do before recording. You will record two segments on each forearm: a. Segments 1 and 3 record Motor unit recruitment.
b. Segments 2 and 4 record Fatigue
SEGMENT 1 – Dominant Arm Motor Unit Recruitment
- Note your Assigned Increment level from the journal.
Based on your calibrated grip force, the software determines the optimal grid display and force increments. Check to make sure that you didn’t exceed 25kg of force and that your assigned increment in the journal window is 5kg : Force calibration Assigned Increment 0-25 kg 5kg TARGET Correct 25-50 kg 10 kg Incorrect redo Calibration
50 kg 20 kg Incorrect redo Calibration
- Click Record. After you click Record , the recording will begin and an append marker labeled “Forearm 1, Increasing clench force” will automatically be inserted. The screen will change to display only the hand dynamometer channel, and a grid using your assigned increment as a division scale will appear so that you can visually review the force level.
- Clench-Release-Wait and repeat with increasing clench force. Hold each clench for 2 seconds – wait 15 seconds to allow recovery between
each clench. Targets are 5-10-15-20-
25-etc. until max clench achieved.
Repeat a cycle of Clench-Release-Wait, clench and holding clench for 2 seconds and waiting for 15 seconds after releasing clench before beginning the next cycle. Begin with 5 kg of force and increase by the 5 kg (5-10-15-20-25 for example) for each cycle until maximum clench force is obtained.
- Click Suspend. The recording should halt, giving you time to review the data.
- Review the data on the screen.
¾ If correct, proceed to recording Segment 2 – dominant arm fatigue test.
Recording continues…
If all went well, your data should look similar to Fig. 2.7.
The important aspect for you to review is that the data shows
multiple peaks (indicating the clench cycles).
The data shown is from a Subject who was able to maintain an
even force throughout the clench. You should have at least 2 seconds of relatively smooth plateau for each clench.
Fig. 2.7 Motor Unit Recruitment
Page 8 http://webs.wofford.edu/pittmandw/psy230/lab.htm EMG Laboratory
The data would be incorrect if the: a. Suspend was clicked prematurely. b. Instructions were not followed.
- If incorrect, click Redo ( this will erase the previously recorded data segment ) and repeat Segment 1.
Click “ Redo ” and repeat Segment 1 if necessary. Note that once you click Redo , the data you have just recorded will be erased.
SEGMENT 2 – Dominant Arm Muscle Fatigue Test
- Click Resume. When you click Resume , the recording will continue and an append marker labeled “Forearm 1, Continued clench at maximum force” will be automatically inserted.
- Clench the hand dynamometer with your maximum force. Note this force and try to maintain it.
Note the maximum clench force so you can determine when the force has decreased by 75% (the maximum force may scroll out of view). Try to maintain the maximum clench force (the forearm will fatigue and the force will decrease).
- When the maximum clench force displayed on the screen has decreased by more than 75% , click Suspend.
The time to fatigue to 50% of maximal clench force will vary greatly among individuals. When you click Suspend , the recording should halt, giving you time to review the data for segment two.
- Review the data on the screen.
If correct, proceed to recording Segment 3 – Non-dominant Arm Motor Unit Recruitment.
If all went well, your data should look similar to Fig. 2.8.
Fig. 2.8 Fatigue Note that the peak found immediately following the start of the Segment represents the maximal clench force. This example shows the point of fatigue to 50% maximal clench force captured on the same screen, but your maximum force may scroll out of view. You may use the horizontal (time) scroll bar to view your entire recording. The data would be incorrect if: a) You didn’t record past the point of 50% maximal clench force. b) Suspend was clicked prematurely. c) The instructions were not followed.
- If incorrect, click Redo ( this will erase the previously recorded data segment ) and repeat Segment 2.
Click “ Redo ” and have the Subject rest so the arm muscles recover and the fatigue data will be meaningful. When ready repeat Segment 2. Note that once you click Redo , the data you have just recorded will be erased.
Recording continues…
Page 10 http://webs.wofford.edu/pittmandw/psy230/lab.htm EMG Laboratory
SEGMENT 4 – Non-dominant Arm Muscle Fatigue Test
- Click Resume. When you click Resume , the recording will continue and an append marker labeled “Forearm 2, Continued clench at maximum force” will be automatically inserted.
- Clench the hand dynamometer with your maximum force. Note this force and try to maintain it.
Note the maximum clench force so you can determine when the force has decreased by 75% (the maximum force may scroll out of view). Try to maintain the maximum clench force (the forearm will fatigue and the force will decrease).
- When the maximum clench force displayed on the screen has decreased by more than 75% , click Suspend.
The time to fatigue to 50% of maximal clench force will vary greatly among individuals. When you click Suspend , the recording should halt, giving you time to review the data for segment two.
- Review the data on the screen.
If correct, click Stop and proceed with the last portion of the EMG lab – Listening to the muscle potentials.
If all went well, your data should look similar to Fig. 2.8. When you click Stop , a dialog box is generated, asking if you are finished with both Forearm recordings. This is simply one last chance to confirm that you don’t need to redo the last recording segment. Click “Yes” to end data recording and automatically save the data. Click “No” to return to a display with a Redo option. The data would be incorrect if: a) You didn’t record to the point of 50% maximal clench force. b) Suspend was clicked prematurely. c) The instructions were not followed.
- If incorrect, click Redo and repeat Segment 4.
Click Redo and have the Subject rest so the arm muscles recover and the fatigue data will be meaningful. When ready, repeat Segment 4. Note that once you click Redo , the data you have just recorded will be erased.
Listening to the EMG – Audio amplification of your forearm muscle potentials
- Subject puts on the headphones. Listening to the EMG is NOT optional. You will be asked to describe this experience in your lab report discussion section.
26. Click Listen.
- As you listen, try a variety of Clench- Release–Wait cycles and watch how the data changes on the screen as you listen to the muscle potentials.
You will hear the EMG signal through the headphones as it is being displayed on the screen. The screen will display three channels: CH 1 Force, CH 3 EMG, and CH 40 Integrated EMG. The data on the screen will not be saved. The signal will run until you click Stop.
- Click Stop. To listen again, Redo. This will end listening to the EMG.
- Click Done. A pop-up window with four options will appear. Make your choice, and continue as directed.
- Remove the electrodes from each forearm.
Remove the electrode cable pinch connectors, and peel off the electrodes. Throw away the electrodes. Wash the electrode gel residue from the skin, using soap and water. The electrodes may leave a slight ring on the skin for a few hours, which is quite normal.
END OF RECORDING
