Lab 4_Electromyography copy

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BIO 240L ELECTROMYOGRAPHY II * Motor Unit Recruitment & Fatigue 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. 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 motor neuron and all of the muscle fibers/cells that the motor neuron makes contact with/innervates. An electrical signal called an action potential (AP) in a human motor neuron always causes a subsequent action potential in all of the muscle fibers associated with the motor unit. In response to the activation of the action potential, the muscle fiber contracts. As a matter of fact, humans generally do not send just one AP at a time down a motor neuron. Instead, a train of AP’s is sent- enough to reduce tetany (the sustained fusion of individual muscle twitches) in the muscle fibers of the motor unit. 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. *Instructions for use with Biopac Systems Inc. software. 1

BIO 240L 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 muscles 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 indicated the bucket is being lifted. The sequential activation of motor units to perform a designated task that requires greater force 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. Skeletal muscles performing acute maximum work or chronic submaximum work of a repetitive nature will eventually fatigue. Fatigue is defined as a decrease in the muscle’s ability to generate force. The time to fatigue is defined at the length of time it takes for the 50% decrease in the muscle’s ability to generate its maximal force. Fatigue is caused by a reversible depletion of the muscle’s fuel supply. If the muscle uses its energy sources faster than it can be generated by cellular metabolism, fatigue occurs. During contraction, skeletal muscle cells convert chemical energy into thermal and mechanical energy, and, in the process, produce chemical waste products. Normally the waste products are removed from the muscle by the circulatory system as the blood brings nutrients to the muscle for energy transformation. If certain waste products (metabolites) are not removed at an adequate rate, they will accumulate and chemically interfere with the contractile process, thereby hastening the onset of fatigue. Some accumulated waste products also stimulate pain receptors in surrounding connective tissue and induce cramping of skeletal muscle, a general sign of inadequate blood flow to the muscle. In this lesson, you will examine motor unit recruitment and skeletal muscle fatigue by combining electromyography with dynamometry . When a motor unit is activated, the component muscle fibers generate and conduct their own electrical impulses, which cause the fibers to contract. Although the electrical impulse generated and conducted by each fiber is very weak (less than 100 volts), many fibers conducting simultaneously induce voltage differences in the overlying skin which are large enough to be detected by a pair of surface electrodes. The detection, amplification, and recording of changes in skin voltage produced by underlying skeletal muscle contraction is called electromyography, and the recording thus obtained is called an electromyogram (EMG) . Power is defined as the amount of work done per unit of time. Dynamometry means the measurement of power (dyno = power, meter = measure), and the graphic record derived from the use of a dynamometer is called dynagram. 2

BIO 240L In this lesson, the power of contraction of clench muscles will be determined by a hand dynamometer equipped with an electronic transducer for recording. The BIOPAC system will simultaneously record three bands of information: 1) The force you exert on the transducer, 2) The electrical signal produced by the muscle during contraction, and 3) The integrated waveform, which is an indication of the activity levels of the muscle. EXPERIMENTAL OBJECTIVES 1) To determine the maximum clench strength for right and left hands and compare differences between males and females. 2) To observe, record, and correlate motor unit recruitment with increased power of skeletal muscle contraction. 3) To record the force produced by clench muscles, EMG, and integrated EMG when inducing fatigue. MATERIALS  BIOPAC electrode lead set (SS2L)  BIOPAC disposable vinyl electrodes (EL 503), 6 electrodes per subject  BIOPAC SS25 Hand dynamometer EXPERIMENTAL METHODS Equipment Setup 3

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BIO 240L Step 1. Turn on your computer. Step 2. Turn on the MP30 unit (switch on the back of the unit) Step 3. Select the BSL 3.7.6 (BSL Lessons) icon on the desktop. Step 4. Choose lesson “LO2emgII” Step 5 . Click OK Step 6 . Enter name in the following format: Lastnamefirstinitialemg2. Step 7 . Plug BIOPAC hand dynamometer into channel 2 and electrode into channel 1 as seen in diagram below. Calibration Step 8. Connect the electrodes to dominant forearm as seen in diagram. Be sure to follow color codes. 4

BIO 240L Step 9. Click Calibrate . Step 10. Set dynamometer down on the bench (so that there is no pressure on it), click OK . Step 11. Pick up dynamometer and hold in proper grip position (upright) as seen in figure below. Click OK . 5

BIO 240L OR Step 12. Click OK , wait two seconds (the time in seconds is shown at the bottom of the window on the computer screen) then clench dynamometer as hard as possible for two seconds then relax. Step 13. Wait for calibration to stop. Step 14 . If calibration is not correct (does not look like the figure below), click redo . If calibration is ok, proceed to the next page and read the instructions before selecting record as the next exercise will begin as soon as record is clicked. Motor Unit Recruitment Step 1. After clicking record student will perform a series of clenches for two seconds and releases for two seconds. Each time the force should be increased depending on increment level. For example, if in increments of five kg of force, students will exert five kg of force in the first time interval, 10 kg in second time interval, etc. The recording should look like the figure on the next page. Step 2. After this is done click on suspend . Step 3 Review data on the screen. If correct click resume , proceed to the next section, “Time to Fatigue”. If not click redo . 6

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BIO 240L Time to Fatigue Please read the instructions in their entirety before starting: Step 1 Click resume Step 2 Clench the hand dynamometer with your maximum force. Note this force on the computer screen and try to maintain it as long as you can. Step 3 When the maximum clench force displayed on the screen is less than 50% of the force you started with (see figure below), click on suspend . Do not stop at the point where the force is exactly 50% of what was initially generated. For example, if the initial force that you exert is 30 kg, do not stop clenching the dynamometer until the force you are able to exert is less than 15 kg. Step 4 Review the data on the screen. If errors were made, click redo Step 5 If the recording is OK, attach the electrodes to other (non-dominant) arm as seen in the diagram on page 6 and click resume to complete the recording of motor unit recruitment and time to fatigue as before (see pgs 6-7) Step 6 After you are done click stop  yes (save recording) Step 7 Remove and dispose of electrodes. Proceed to Data Analysis 7 Force at 50% fatigue Initial force

BIO 240L Data Analysis (See page 10 for the tables in which you will be recording your data) I. Motor Unit Recruitment Step 1 click stop  yes (save recording) Step 2 Click OK . Step 3 Scroll to the beginning of the recording (dominant arm motor unit recruitment) Step 4 Change the drop-down menu in the top left-hand corner of the computer screen (labeled “none”) to change the headings as shown below (arrows): Mean p-p mean For MP36 units: Mean p-p Step 5 Click on the I-beam cursor (bottom right hand side of data window) highlight the first interval (2.00 seconds to 4.00 seconds; see below). 8 41 1 40 2 1 40

BIO 240L Note there are now values in the mean and p-p windows on the top left-hand corner of the screen (arrows in the image above). Record these values in the table on the next page for each of the peaks in the recording (note you will not necessarily have nine peaks to measure): II. Time to Fatigue Step 1 Scroll to the second recording segment: Step 2 Use the drop-down menu in the top left hand corner of the computer screen to change the headings on the data window as indicated below: Max none ΔT Step 3 Highlight the second segment until 50% fatigue (see below), record the values in the table below. 9 41 1 40

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BIO 240L Step 4 Repeat the analysis above for the non-dominant forearm. Step 5 Exit the program (file  quit) 10

BIO 240L Student Name _________Jirolna Joseph__________ Data Collection Motor unit recruitment and Fatigue I. Motor Unit Recruitment Subject Profile: Age __19_ Gender ___Female____ Height ___5’5_____ Enter the force increments you attempted in column 2 below. For example, 5, 10, 15 kg. The “force at peak” column next to it will be used to record the actual force you generated . Dominant Arm, Motor Unit Recruitment Forearm 1 (Dominant) Peak # Attempted force increments (kg) Force at Peak (mean; CH41) Kg Raw EMG (p-p; CH1) mV Integrated EMG (mean; CH40) mV/s -1 1 10 9.489423 1.130981 0.113916 2 10 9.290651 1.500854 0.164991 3 10 8.661345 1.791381 0.148493 4 10 10.680517 1.644897 0.173886 5 10 6.310522 1.632080 0.124383 6 Dominant Arm, Time to Fatigue *NOTE: You do not need to indicate the delta T (time to fatigue) polarity. The polarity of the delta T measurement reflects the direction the “I-beam” cursor was dragged to select the data. Data selected left to right will be positive (+), while data selected right to left will be negative (-). Leave the + or – sign out of your response. 11 Forearm 1 (Dominant) Maximum Clench Force 50% of max clench force Time to Fatigue (0.5 point) CH1 Value Calculate (0.5 point) CH40 delta (Δ) T* 13.689313 off 10.158000

BIO 240L Non- Dominant Arm, Motor Unit Recruitment Forearm 2 (Non-Dominant) Peak # Attempted force increments (kg) Force at Peak (mean; CH41) Kg Raw EMG (p-p; CH1) mV Integrated EMG (mean; CH40) mV/s -1 1 10 4.972191 1.335449 0.152747 2 10 7.248601 1.254882 0.137330 3 10 8.696300 1.530761 0.151450 4 10 10.365185 1.573486 0.153112 5 10 12.786301 1.985473 0.206127 6 10 Non-dominant Arm, Time to Fatigue III. Questions Note: Please do not copy the definitions verbatim from the handout. A. Is the strength of your right arm different from your left arm? ____ Yes ____ No B. Is there a difference in the absolute values of force generated by males and females in your class? ____Yes _____ No; If yes, any ideas on why this may be the case? (1 point) ____________they exercise their muscle fibers more often then the females._______________________________________________________________ ___________________________________________________________________________ C. Yes or No - When holding an object, does the number of motor units remain the same? (0.5 point) __________no____________ Are the same motor units used for the duration of holding the object? ____no______ (0.5 point) 12 Forearm 2 (non-Dominant) Maximum clench force 50% of max clench force Time to fatigue 0.5 point CH1 value Calculate (0.5 point) CH 40 delta (Δ) T* 13.689313 off 8.962000

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BIO 240L Explain (2 points) ____they are being fired to help with the holding of the objects. As time passes they start to get weaker due to fatigue_______________________________________________________ __________________________________________________________________________ __________________________________________________________________________ D. As you fatigue, the force exerted by your muscles decreases. What physiological processes explain the decline in strength? (1.25 point) ___fatigue explains the decline in the muscles ability to generate force._______________________________________________________________________ __________________________________________________________________________ E. Define the term motor unit (0.75 point) ____motor neuron in all of the muscle fibers that the motor neuron makes contact with.________________________________________ __________________________________________________________________________ F. Define motor unit recruitment. (0.75 point) _____the sequential activation of motor units to perform a designated task that requires greater force.____________________________________ ___________________________________________________________________________ G. Define fatigue as it relates to muscle function (0.75 point) ____when the muscle loses the maximum strength it had over time.________________________ ___________________________________________________________________________ H. Define electromyography (0.75 point) _________the recording of the electro activity of muscle tissue___________________________________ __________________________________________________________________________ I. What is dynamometry? (0.75 point) ________the measurement of power._____________________________________ __________________________________________________________________________ 13

Lab 4_Electromyography copy

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