Motor unit recruitment and force production with and without fatigueLAB WRITE-UP (max 3-4 sentences each)WHAT YOU ARE TURNING INMotor unit recruitment KIN 460 – Motor Control Lab Section 1 Lab 3: Principles of Motor Unit Recruitment and Muscular Force Production Motor unit recruitment and force production with and without fatigue Introduction Over the last week in class you have learned about how electrical signals lead to the contraction of muscular tissue (excitation-contraction coupling cycle). The cells responsible for sending the descending signals to the muscle fibers are known as motor neurons. Motor neurons have different properties that influence how muscle is activated. They can be classified as slow, fast fatigue-resistant, and fast fatigable (the size of the cells in each class get progressively larger). Because each cell type has different force producing capabilities (larger cells produce more force than the smaller ones), larger cells are progressively recruited as they are needed (see the left panel in the figure above). Because there are multiple ways to perform a movement, movement poses a problem for the nervous system. Control of movement is primarily organized hierarchically: movement goals are formulated by higher brain areas while the activation of specific muscle fibers is determined by neural processes in the spinal cord. Purpose To study the recruitment of motor units for force production. • To understand the changes in force production over time under different degrees of effort • To understand how these force changes are related to the properties of the motor neurons that innervate the musculature involved • To understand what electromyography (EMG) is and what the signal being recorded represents BEFORE BEGINNING THE LAB BUT AFTER READING THE INSTRUCTIONS AND GAINING A BETTER UNDERSTANDING OF THE NATURE OF THE EXPERIMENT, DEVELOP A HYPOTHESIS FOR THIS EXPERIMENT AND WRITE IT DOWN. THIS WILL BE INCLUDED IN YOUR LAB REPORT. Setup 1. Set up each workstation accordingly. Make sure you have: a. Computer with Biopac MP3X unit b. Hand dynamometer c. EMG electrode lead set d. Three disposable vinyl electrodesMotor unit recruitment KIN 460 – Motor Control Lab Section 1 2. Plug the electrode lead set for the forearm into channel 1 and the hand-grip dynamometer into channel. Attach the electrodes to the forearm. The black lead (ground) should be on radial styloid, the white lead (negative) should be on the flexor carpi radialis muscle and the red lead (positive) should be 3 inches from the white lead towards the radial styloid. a. To find the flexor carpi radialis of your dominant arm, hold your arm down to your side and clinch your fist and curl your wrist towards your face (flexing your wrist while clinching). Your flexor carpi radialis (and the ulnaris) are the muscles of your forearm on the medial side, about three fingers away from the crevice of your elbow. When you clinch and curl, the muscles should be firm. 3. Start the Biopac program and load the lesson 2, titled EMG II. 4. Type your name Calibration 1. Click ‘calibrate’, set dynamometer down and click OK. 2. After baseline calibration has been completed, you will need to get a calibration for the maximum force you can produce. When prompted, grip the dynamometer as hard as you can for at least two seconds. Data Recording 1. Click ‘record’ and perform clench-release cycles for 2 seconds in 10 kg increments until you perform at your maximal strength. 2. After you reach your max strength for two cycles in a row, squeeze as hard as you can for as long as you can, until your force output falls to approximately 75% less than that of the highest value. 3. When finished, click ‘suspend’. 4. Review the data on the screen. Click ‘stop’ if you are finished. If you need to redo data collection, then click ‘redo’. If not, click “done” and proceed to the next step. Data Extraction 1. Click on “Analyze Current Data File” 2. Click on the I-Beam cursor button and highlight the portion of the data set that contains your clenche-release cycles (highlight ~1 second before the first clench and after you finished the last clench). 3. Click on “Edit”, then “Data Window”, then “Copy Wave” 4. Paste the data into an Excel spreadsheet and name the tab “Clench Cycles”. 5. Repeat the process again for the long duration contraction and paste into a different tab in the spreadsheet. 6. Save the Excel document on the PC. After you’ve completed the entire lab send the Excel document by email or use a flash drive to export the document to your own computer. DATA ANALYSIS 1. Graph 1: Graph your clench-release cycle data as a dual-y axis scatterplot (straight lines without markers). One line is the force data (kg), and one line is the integrated EMG activity (mV) with time (seconds) on the X-axis. Put a secondary y-axis on the graph for either the force data or the EMG data. Remember to include a legend that indicates force and EMG data. 2. Graph 2: Once you have made graph 1 from above, you will now look at the data you have and calculate an average across each of the individual plateaus from both the EMG data and the Force data (only during the flat portion!). You should now have one data point for each plateau for each curve. Normalize each of your data points to the largest value within that class of data. If you have six clench-release cycles, you should have six data points from your force data and six from your EMG data. You will now need to make a scatter plot with straight lines with your 12 data points. The EMG data will be the x-axis values, and the Force data will be the y-axis values. Make sure you indicate all necessary information for the graph and include a trendline (what is the slope of this line?).Motor unit recruitment KIN 460 – Motor Control Lab Section 1 3. Graph 3: Repeat the steps from graph 2 with your fatigue data, except this time take samples of data (25 data points each? Ask your instructor for guidance) at regular intervals from the force and EMG data (must use same intervals). Plot a line graph with the EMG on the x-axis and the force on the y-axis using scatter plot with straight lines. Make sure you indicate all necessary information for the graph and include a trendline (what is the slope of this line?). LAB WRITE-UP (max 3-4 sentences each) 1. Based on your own data and your current