Lab 1: Analysis of Muscle Function PDF

Graphical Analysis 15 Analysis of Muscle Function Muscle tissues maintain electrical imbalances, or potentials, across cell membranes by concentrating positive or negative charges on opposite sides of those membranes. These potentials are a form of stored energy. With activation (su...

Graphical Analysis 15 Analysis of Muscle Function Muscle tissues maintain electrical imbalances, or potentials, across cell membranes by concentrating positive or negative charges on opposite sides of those membranes. These potentials are a form of stored energy. With activation (such as from a nerve impulse), the ions are allowed to cross the muscle cell membranes, generating electrical activity that results in muscle contraction. An electromyogram, or EMG, is a graphical recording of electrical activity within muscles. It is useful in the diagnosis of disorders affecting muscles and the nerves that supply them. Inherited and acquired disorders of muscles (such as the muscular dystrophies), as well as disorders of the central and peripheral nervous systems (such as Huntington’s disease and diabetic neuropathy), result in abnormal EMG readings. Figure 1 EMG studies are also useful for investigating normal muscle function. In this experiment, you will analyze electrical activity in the extensor muscles of the forearm. These muscles originate in tendons of the proximal dorsal forearm in the region of the lateral epicondyle and attach distally to tendons that control extension of the hand and fingers (see Figure 1). Inflammation of the tendons at the elbow is common and can result from repetitive motions used in sports, hobbies, and in the workplace. This condition, lateral epicondylitis, is commonly known as tennis elbow, but can result from any activity in which repetitive gripping occurs, especially between the thumb and first two fingers. This experiment will examine the differences in muscle activity in the forearm extensors when hand position is changed. Important: The equipment used in this experiment is for educational purposes only and should not be used to diagnose medical conditions. OBJECTIVES  Obtain graphical representation of the electrical activity of a muscle.  Associate muscle activity with movement of joints.  Correlate muscle activity with injury. Human Physiology Experiments: Volume 2 © Vernier Software & Technology 1 Analysis of Muscle Function MATERIALS Chromebook, computer, or mobile device Graphical Analysis 4 app Go Direct EKG electrode tabs ruler 1–2 kg (3 lb) weight (barbell or similar) PROCEDURE Select one person from your group to be the subject. Important: Do not volunteer to be the subject if you suffer from arthritis, or other conditions of the hand, wrist, forearm, or elbow. Note: Save the file with the name (L1_ALP_HP2_15_GroupNO). Copy the data files on a CD and give it to your colleagues in the group so that they can analyze the data. 1. Connect and set up the sensor. a. Launch Graphical Analysis. b. Connect Go Direct EKG to your Chromebook, computer, or mobile device. c. Click or tap Sensor Channels. Deselect the EKG channel and select the EMG Rectified channel. d. Click or tap Done. 2. Click or tap Mode to open Data Collection Settings. Change Rate to 100 samples/s and End Collection to 25 s. Click or tap Done. 3. Attach three electrode tabs to your dominant arm, as shown in Figure 2. Two tabs should be placed on the dorsal forearm, 5 cm and 10 cm from the lateral epicondyle along an imaginary line connecting the epicondyle and the middle finger. A third electrode tab should be placed on the upper arm. 4. Connect the EKG clips to the electrode tabs. The red and green clips should be connected to the tabs on the subject’s forearm and are interchangeable for this experiment. Connect the black clip to the tab on the upper arm. Figure 2 5. Instruct the subject to stand facing the table or lab bench and rest the fingertips on the table (hand will be pronated), with the palm above the surface and in line with the forearm (see 2 Human Physiology Experiments: Volume 2  Analysis of Muscle Function Figure 2). Start data collection. If the graph has a stable baseline, stop data collection and continue to Step 6. If the graph has an unstable baseline, stop data collection and try again until you have a stable baseline for 5 s. You may need to reposition the electrodes to get a stable baseline. 6. Collect data while flexing and relaxing the extensor muscle. a. Click or tap Collect to start data collection. b. After recording a stable baseline for 5 s, instruct the subject to gently extend his or her hand as far as possible (without pain) (see Figure 3). Hold this position for 5 s. c. After the 5 second hold, the subject can return to the relaxed position, with fingertips resting on the table surface, for a period of 5 s. d. Instruct the subject to repeat the extension and relaxation action for one more full cycle— 5 s with the hand extended, followed by 5 s with the hand in a resting position. Data will be collected for 25 s. Figure 3 7. Measure the integral of the EMG graph. a. Using the EMG graph, click or tap Graph Tools, , and choose View Integral. b. Record the area reported in Table 1, rounding to the nearest 0.01 mV s. c. Dismiss the Statistics box. 8. Repeat Step 7 to highlight each of the next 5 s intervals until you reach 20 s (5–10 s, 10–15 s, 15–20 s). Record the area for each interval in Table 1. Ergonomics and Muscle Protection 9. Obtain a 1–2 kg (3 lb) weight (barbell or similar) from your instructor. 10. Instruct the subject to place his or her relaxed hand on the weight, with the palm facing downward. Start data collection. If the graph has a stable baseline, stop data collection and continue to the next step. If the graph has an unstable baseline, stop data collection and repeat data collection until you have obtained a stable baseline for approximately 5 s. 11. Collect data to examine the effect of lifting a weight using the extensor muscles: a. Click or tap Collect to start data collection. b. After recording a stable baseline for 5 s, instruct the subject to grip the weight with the hand. Using only the action of the wrist, instruct the subject to extend the hand to lift the Human Physiology Experiments: Volume 2 3  Analysis of Muscle Function weight to a height of 5–10 cm off the surface of the table (Figure 3) and hold this position (extended) for 5 s. c. Instruct the subject to gently lower the weight onto the table and rest for 5 s. d. Instruct the subject to repeat the extension and relaxation action for one more full cycle— 5 s with the hand fully extended, followed by 5 s with the hand in a resting position. Data will be collected for 25 s. 12. Measure the integral of the EMG graph. a. Using the EMG graph, click or tap Graph Tools, , and choose View Integral. b. Record the area reported in Table 1, rounding to the nearest 0.01 mV s. c. Dismiss the Statistics box. 13. Repeat Step 12 to highlight each of the next 5 s intervals until you reach 20 s (5–10 s, 10–15 s, 15–20 s). Record the area for each interval in Table 1. 14. Instruct the subject to place your hand, palm facing upwards (hand will be supinated), under the weight, and lightly grip it (see Figure 4). Start data collection. If your graph has a stable baseline, stop data collection and continue to the next step. If your graph has an unstable baseline, stop data collection and repeat data collection until you have obtained a stable baseline for approximately 5 s. Figure 4 15. Collect data while lifting a weight using the flexor muscles: a. Click or tap Collect to start data collection. b. After recording a stable baseline for 5 s, instruct the subject to use only the action of his or her wrist to lift the weight to a height of 5–10 cm off the surface of the table and hold this flexed position for 5 s. c. Instruct the subject to gently lower the weight onto the table and rest for 5 s. d. Instruct the subject to repeat the flexion and relaxation action for one more full cycle–5 s of flexing upward with weight, followed by 5 s with the hand in a resting position. 16. Measure the integral of the EMG graph. a. Using the EMG graph, click or tap Graph Tools, , and choose View Integral. b. Record the area reported in Table 1, rounding to the nearest 0.01 mV s. c. Dismiss the Statistics box. 4 Human Physiology Experiments: Volume 2  Analysis of Muscle Function 17. Repeat Step 16 to highlight each of the next 5 s intervals until you reach 20 s (5–10 s, 10–15 s, 15–20 s). Record the area for each interval in Table 1. DATA Table 1 Condition Interval (approximate) Area (mV s) Fingers resting on table Hand extension Fingers resting on table Hand extension Fingers resting on weight–hand pronated Hand extension with weight Fingers resting on weight–hand pronated Hand extension with weight Fingers loosely gripping weight–hand supinated Hand flexion with weight Fingers loosely gripping weight–hand supinated Hand flexion with weight DATA ANALYSIS 1. Reviewing your data, what conclusion can you reach regarding the relationship between the strength of muscle contraction and the area of electrical activity generated? 2. What do the results in Table 1 show about the relationship between hand position and muscle activity when lifting an object? 3. What advice would you give to a friend with tennis elbow about how she should lift a frying pan onto the stove or a can of paint onto a workbench? 4. Some people use a computer keyboard or mouse with the wrists resting on the table or on a wrist support. In light of what you have learned from this experiment, would you recommend this practice as a way of preventing injury to the extensor muscles of the forearm? Why or why not? 5. Based on this experiment, what advice would you give to a beginning piano player about proper hand position? Human Physiology Experiments: Volume 2 5 Analysis of Muscle Function 6. Pitcher’s elbow is a repetitive use injury of the medial epicondyle. What do the muscles that attach to the medial epicondyle control? How would you adapt this experiment to test these muscles? EXTENSION When setting up the electrodes for the EMG, the leads may be placed on the ventral forearm instead of the dorsal forearm. The remaining steps can then be carried out without change. Explain the resulting EMG tracing. 6 Human Physiology Experiments: Volume 2