LINEAR KINEMATICS of HIGH HEEL WALKING Objective: The objective of this lab is to manipulate linear kinematic data in order to discuss the kinematic differences between walking in flat shoes and walking in high-heeled shoes. Methods: A volunteer walked through the Biomechanics Lab at 1.6 m/s with flat shoes and with 4" (9 cm) high-heeled shoes. Refelctive markers were placed over various anatomical landmarks and the subject was video taped at 60 Hz (frames per second). The raw data were processed to provide coordinate data for the hip, knee, and ankle for both the high-heel and flat-shoe conditions. These data have been normalized to one stride: heel strike to successive heelstrike. By manipulating and graphing the data, you should be able to answer the disussion questions. Analysis: Download the data file for Excel or as a text file. Download the analysis and discussion procedures as a Word document or as a text file. In Excel (or Lotus, Quatro, ClarisWorks) create a spreadsheet and open your newly downloaded data file. In this data file you will find the vertical displacement data for the hip, knee, and ankle markers of the subject. The first column is the X-axis data expressed as percent stride. There are 3 columns of data for the bare foot condition and 3 columns for the high heel condition. Thus, you should have seven (7) columns of data with 50 rows of numbers. Since the high heel shoe condition modifies the vertical displacement data by a consistent amount (by the height of the heel), comparison between the conditions will be facilitated if we correct for this effect. This is done by calculating the difference between the lowest high heel ankle displacement and the lowest bare foot ankle displacement. This difference represents the heel height. Calculate heel height and subtract it from the high heel data, entering it into 3 new columns in your spreadsheet. Using these data create a plot of the flat shoe and the corrected high heel displacements with respect to percent stride. This plot should contain six lines, two for each marker. Examine this plot and note any significant differences among the conditions for later discussion. The next step is to differentiate the displacement data to obtain the vertical velocity of each marker. Differentiation, in this case, will be to estimate the INSTANTANEOUS velocity. A detailed set of instructions can be found by clicking here. Using these instructions, compute the instantaneous velocity for each of the markers. Since our velocity calculation involves the difference in displacement between points, both the uncorrected and corrected data will give the same result - you may use either data set in your calculation of high heel marker velocities. In order to complete the calculations, you must know the time interval between data points. It is 0.0177 s for the high heel condition and 0.0187 s for the flat shoe condition. You should now have 16 columns of data. Using these data create a plot of the marker velocity with respect to percent stride. You will need to plot 3 separate graphs, one for each marker with the two conditions. Heel strike occurs at first and last frames and toe off occurs at 65.3% stride for the flat shoe condition and 57.1% stride for the high heel condition. Mark toe off for each condition on each of your graphs. Discussion - fundamental concepts 1. Why did we estimate the instantaneous velocity rather than calculating average velocity? 2. What is significant about the displacement values when the velocity is zero? (Hint: Look on your graphs and compare displacement and velocity.) 3. What process would you use to compute the displacement if you had only the velocity data? 4. How would you compute the acceleration data for these markers? Discussion - applied issues 1. Characterize the two fundamental differences between the high-heel and flat shoe conditions seen in the displacement graph. 2. Calculate the stride time for each condition. Calculate the stance time for each condition. Why do you suppose that the high-heel stance time is shorter than the flat-foot stance time? 3. There is an amplitude difference in ankle displacement just after toe-off. Why is this not reflected by an amplitude difference in the ankle velocity at this time?
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