5. Initial Twitch Experiment: a. Set the Stimulator Machine to: i. Voltage = 20 V ii. Duration of the stimulus = 2 msec iii. Frequency = single pulse b. c. Look at the fingers and deliver a stimulus by pressing “Single” stimulus. Determine if a twitch was seen. i. If so, then this is your threshold setting. Move on to “Step 5-f”. ii. If not, then continue to the next step. d. Change the Voltage to 30 V and deliver a stimulus by pressing “Single” stimulus. e. Determine if a twitch was seen. i. If so, then congratulations you found the proper motor points. Move on to “Step 5-f”. Do not move the electrodes for the rest of this experiment. ii. If not, adjust the electrode placement and repeat this experiment until you see a twitch. You may need to increase the voltage on folks with larger muscles. Ask for support if needed. f. At which voltage did you see a twitch? __________ V 6. Twitch Threshold Experiment: a. Begin by using the settings that you determined in the Initial Twitch Experiment. i. Set the Stimulator Machine to: 1. Voltage = __________ V (taken from Step 5-f) 2. Duration of the stimulus = 2 msec 3. Frequency = single pulse (1 Hz; 1 pulse per second) b. For each test, lower the voltage in a stepwise manner until you determine the threshold. Look at the fingers and deliver a stimulus by pressing “Single” stimulus. c. Determine the lowest voltage needed to stimulate a twitch. i. What is the lowest voltage needed for you to see a twitch? __________ V ii. When stimulating your volunteer using the Twitch Threshold settings, you are recruiting the ____________________ [small / medium / large] motor units.
