Biomechanics Laboratory E Ground Reaction Forces in Locomotion Introduction The purpose of this laboratory is for students to become familiar with the similarities and differences between the ground reaction forces in walking and running. Data will be collected at two different speeds within each gait. This will allow not only for an assessment of the differences between walking and running, but also for the effects of speed within each gait form. Methods Participants A group of 3-4 students will work together at a single workstation. Walking and running data will be collected on one volunteer from each group. What you need for this lab: Bring a USB flash drive (aka: a memory stick, thumb drive, etc.) Wear athletic shoes - no sandals, flip-flops, or dress shoes. Equipment Each workstation will consist of a desktop computer for data collection and a force plate that interfaces with PASCOairlink. The force platform records forces in the vertical direction at a sampling frequency of 100 Hz (samples per second). Procedures The participant will walk and run across the force platform at 2 speeds for each gait (i.e., slower walking and faster walking; slower running and faster running). The student will attempt to maintain a steady speed and a normal gait pattern while striking the force platform with his or her right foot. Due to the somewhat limited space in the lab, coordinate your data collection with the lab groups around you. Steps for data collection: 1. Choose a participant, a computer operator, and 1-2 observers. The participant walks and runs, the computer operator will perform steps 2-7 below, and the observers will make sure the participant is performing the correct trial and striking the force plate cleanly. 2. Open the PASCO Capstone icon on the desktop. Select the option that says Two Displays. Once a new window has opened, click the center icon within the top box and select Graph. Once the graph is open, choose <Select Measurement> on the y-axis and choose Normal Force (N). For the x-axis, select Time. 3. Follow the same steps for the bottom box, but select Parallel Force (N) for the y-axis measure. 4. Before any data are collected, zero the force plate. With the plate unloaded, click the small black round TARE button on the side of the force platform where the cable connects. Make sure to set the sampling frequency to 100 Hz at the bottom center of the page.5. Have the participant stand on the force plate. Click the red round Record button in the lower left-hand corner of the screen. A stable line should appear in the Normal Force graph. Press the Stop button once a stable measurement is achieved. Record the participant’s weight in newtons (N) using the coordinates tool in the task bar above the graphs. Weight ___________________ N 6. Data Collection: Before each trial, the computer operator will push the red Record button, and then call out for the participant to walk or run. First, the participant will walk slowly over the force plate, stepping on it with one foot. A real-time force trace will appear as the participant walks over the sensor. Press the red Stop button to end the data collection run. The data is not yet saved, but the program is ready for this same student to perform the next trial in the same manner as above, which will be named Run #3. 7. Continue with a faster walking trial, followed by a slow run and a faster (medium speed) run. Remember: (1) before each trial the computer operator must click the red Record button and (2) after each trial, the computer operator must push Stop to prepare the computer for the next trial. 6. After the last running trial, export the data (five runs in one file (Body weight trial + 4 conditions) to a thumb drive. Use the drop-down menu (“Export...”). Export it as a .csv file, naming it “LocomotionGRF.csv”. Make sure everyone in your group gets a copy of the data. The data will be analyzed in Excel as described in the assignment section below. Assignment You should analyze the vertical ground reaction force data collected in your own lab group. You will need to complete and turn in a lab report, following the template provided on Moodle (see linear kinematics lab). Be sure to include the following in your lab report. 1. Using Excel (or other computer software), make graphs of the vertical ground reaction forces for each of the four conditions (4 figures total). Create a time column, based on the sampling rate that was used to collect the data. Use these time data for the x-axes in your graphs, and the ground reaction forces for the y-axes. Be sure to scale the x- and y-axes so that you can clearly see the ground reaction forces. See the next page for an example of an acceptable graph and an unacceptable graph. 2. Create a table that contains the following data, and include this table in your lab report (an example of the layout of the table is provided on the next page). Determine the peak vertical ground reaction force for each of the four conditions. Express these results as multiples of the subject’s body weight (i.e., if the force is 923 N and the subject’s body weight is 698 N, the force would be presented as 1.32 BW). Also, determine the amount of time that the foot spent on the ground for each gait/speed combination. 3. Compare the general appearance of the vertical ground reaction forces for walking and running. a. Address the similarities and differences in the curves for walking and running (compare fast walking to slow running). b. Address the effects of speed within each gait. Compare similarities and differences between the slow and fast walking curves and, separately, between the slow and fast running curves. 4. Describe the differences in GRF at mid-stance for walking versus running. Why are these different, specifically in terms of COM acceleration? (Hint: look at acceleration from Lab B and think F=ma)5. Recalling the linear kinematics lab (Lab B), where there were displacement differences in the center of mass vertical motion between the walking and running conditions, describe the link between peak vertical ground reaction force and vertical displacement of the center of mass. 6. Briefly describe how stride frequency and foot contact time changes as horizontal velocity increases. How does changing the foot contact time relate to the peak vertical ground reaction force as the horizontal velocity increases from slow walking