# UMass Amherst KIN 430 - BiomechLabB (2 pages)

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## BiomechLabB

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- Pages:
- 2
- School:
- University of Massachusetts Amherst
- Course:
- Kin 430 - Biomechanics

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Biomechanics Laboratory B Linear Kinematics Introduction The purpose of this laboratory is to demonstrate the relationships between linear position displacement and velocity during steady state human locomotion Using the linear position of a marker placed close to the whole body center of mass the displacement and velocity and acceleration can be computed and analyzed Finite difference formulas First Central Difference Method and Forward and Backward Difference Methods will be used to calculate the velocity values Methods Subjects Some students will be asked to run and walk through the motion capture field with a reflective marker placed on the sacrum Several trials will be performed covering a range of speeds Equipment Qualysis motion analysis system Procedures The participants will be asked to walk and run across the force platform in the center of the lab which will assure that the participant s movements are captured by the motion analysis system The participants will attempt to maintain a steady speed while passing through the field of view of the cameras The digital video cameras will record the motion at 240 Hz 240 samples per section The Qualysis system will automatically determine the three dimensional position of the sacral marker throughout the capture volume For this lab we will assume that the marker on the sacrum provides a good estimate of the motion of the center of mass a reasonable assumption Following the lab the data for a complete stride of walking and a complete stride of running will be posted to the class blog in MS Excel format The CM positional data can be differentiated to produce an estimate of the instantaneous velocity over the full stride The CM velocity data can then be differentiated to produce an estimate of the instantaneous acceleration over the full stride This will require three formulas 1 First Central Difference Method vi xi 1 xi 1 2 t 2 Forward Difference Method v1 x2 x1 t 3 Backward Difference Method vn xn xn 1 t vi velocity at time i xi 1 position at time i 1 xi 1 position at time i 1 t change in time time interval n number of data points Assignment You will use the position time data provided on the course Moodle site to analyze the horizontal and vertical displacement and velocity of the whole body center of mass for both walking and running You will need to complete and turn in a lab report following the provided template You will submit your lab report through Turnitin on the course Moodle site Be sure to include the following in your lab report 1 Use the appropriate finite differentiation formulas to determine the horizontal and vertical velocities for all data points in Excel In addition you must show your work for at least one calculation using each of the three differentiation procedures forward difference central difference and backward difference 2 Prepare two tables one for walking one for running with seven columns each time horizontal position vertical position horizontal velocity vertical velocity horizontal acceleration and vertical acceleration From these tables report only the first five time points and the last five time points 3 Using Excel make graphs of horizontal displacement vs time vertical displacement vs time horizontal velocity vs time vertical velocity vs time horizontal acceleration vs time and vertical acceleration vs time for both walking and running twelve graphs total Use all of the data points for creating the graphs not just the first five and last five 4 In the results and discussion sections of your lab report be sure to address the following a Compare the vertical displacement of the center of mass for the two forms of locomotion that you studied Discuss how and why the vertical displacement of the center of mass differs between walking and running b Determine the magnitude of the average horizontal velocity for both walking and running Compare these average values to the instantaneous horizontal velocities which are shown in the graphs that you created c Based on the vertical velocity vs time graphs describe the similarities and differences between walking and running for the vertical velocity of the center of mass d The center of mass horizontal position may be negative or positive but the vertical position will always be positive examine your graphs to confirm this Discuss why this is true Note In order to receive full credit your graphs must be properly formatted Each graph must include a title an X axis label and a Y axis label The ranges on the X and Y axes should be scaled so that your data fills most of the graph See your lab TA for more detail

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