MVCC Kinesiology & Physics Center of Mass for Biomechanical Analyses Lab Report

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lxenfunq

Science

Moraine Valley Community College

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This lab is for Kinesiology but it involves physics. The lab must be completed and a lab report as well using the provided template.

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Name: Date: Lab #2: Center of Mass INTRODUCTION Determination of the body's center of mass is an important part of most biomechanical analyses. Typically a balance board method is used to determine the center of mass location for a static situation. While this is an accurate and straight forward method, it is not practical for analyzing an activity with a range of body positions. For such an analysis, an alternative approach is to determine the center of mass location from an image of the motion at some point or points in time. This might be done from a printed photo or from a series of frames of cine film which record a complete movement pattern. The details of this approach are outlined below. METHODS The center of mass is an ideal point about which the torques due to body segment weights is zero. It can be determined in the following manner: 1. Choose some arbitrary reference point as origin of the coordinate system to be used. 2. Determine the center of mass location of each segment of the body (x, y-pair of coordinates). 3. Calculate the torque about the reference point due to each segment (based on the segment's mass and position). 4. Sum the torques about the reference point for all the segments (one sum for x-direction and one for y-direction). 5. Divide the sum of the torques by the total body mass to determine the center of mass location with respect to the reference point. In applying this method to real situations, anthropometric information about human body segments is used to determine the location of each segment's center of mass and each segment's mass. Each of these body segment parameters (BSP) is usually expressed as a percentage value. In the case of location of the segment's center of mass, it is described as a percent of segment length from the proximal end. In the case of segment mass, it is described as a percent of total body mass. Such BSP data come from cadaver studies performed in various labs during the past century. The most frequently cited of these studies are those of Dempster (1955) and Clauser, McConville and Young (1969), which are based on cadaver dissection studies. One frequently cited source of BSP's was published by Plagenhoef et al (1983). Summaries of these studies are included in many textbooks (e.g., Hamill & Knutzen, 2015, p. 449-455). COMPUTING BODY CENTER OF MASS The body center of mass can be computed from the center of masses and the masses of the segments: (x, y) = coordinates of the body center of mass i = segment number (xi, yi) = the x & y coordinates of the body center of mass of segment i mi = mass of segment i In other words, the body center of mass coordinates are equal to the sum of the products of segmental mass and segmental CM coordinates divided by the body mass (∑mi). In applying this method to real situations, anthropometric information about human body segments is used to determine the location of each segment's center of mass and each segment's mass. Each of these body segment parameters (BSP) is usually expressed as a percentage value. In the case of location of the segment's center of mass, it is described as a percent of segment length from the proximal end. In the case of segment mass, it is described as a percent of total body mass. Such BSP data come from cadaver studies performed in various labs during the past century. The most frequently cited of these studies are those of Dempster (1955) and Clauser, McConville and Young (1969). Summaries of these studies are included in many textbooks. As an example of how these body segment parameters are used, consider a male's thigh segment located as illustrated in the figure. If this person's whole body mass was 80 kg, the thigh mass can be determined as a percent of 80 kg, ie. 10.5% of 80 = 8.4 kg (where 10.5% is the thigh segment mass percent from Plagenhoef). The thigh center of mass location can be determined from the proximal and distal point coordinates and the segment length percent. If for the thigh the center of mass is located at about 43.3% of the length from the proximal end, the specific coordinates can be determined as follows: Segment CM X Position = Xproximal + (Length %) (Xdistal - Xproximal) Xthigh = 10 + (.433) (70 - 10) = 35.98 Ythigh = 30 + (.433) (40 - 30) = 34.33 DATA Whole body center of mass determination is based upon knowing segmental center of mass locations which in turn are based upon segmental end point positions. 1. First, determine each segment's end points. In the figure below, proximal and distal ends of left side segments have been marked. Segment X (cm) Y (cm) L Toe 178 288 L Heel 158 277 L Ankle 167 286 L Knee 131 335 L Hip 87 257 L Shoulder 72 149 L Elbow 87 101 L Wrist 97 40 L Finger Tip 88 12 R Toe 67 467 R Heel 102 449 R Ankle 88 441 R Knee 76 354 R Hip 58 267 R Shoulder 60 155 R Elbow 102 198 R Wrist 131 224 R Finger Tip 156 243 Base of Neck 60 140 Head Top 89 44 2. Use the endpoint coordinates to determine segment center of mass coordinates. Enter segment endpoint coordinates into a spreadsheet arranged something like the illustration below. Add a column which has segmental length percent (as shown in red). Then using the formula described in the lab, determine each segment's center of mass location. 3. Combine these segment coordinates with segment masses to determine each segment's torque about some reference point (the origin). Once segmental center of mass positions are known, these can be used with the segment mass percent to determine a "torque" about an axis. This is really a mass * length calculation. If the torques created by each segment are summed the result is equal to the torque of the whole body mass acting at the center of mass location. This idea allows determining the unknown whole body CM location. In your spreadsheet, add a column with the segment mass percent. Then write formulas for each segment's torque in each direction. Finally, sum the torques and divide by total body mass (100%). 4. Use total torque to determine whole body center of mass location. PROCEDURE 1. On a relatively large picture of a human in action, determine locations of the following anatomical landmarks: toe, heel, ankle, knee, hip, shoulder, elbow, and wrist, third knuckle (MCP), C7-T1 and top of head. For data collection, a printout of a data table will simplify recording of coordinate information. Use the attached picture of a runner for your analysis. 2. Enter the segment end point coordinates into a spreadsheet. Combined with segment length percent, determine segment center of mass locations. 3. Using segmental mass percent, determine torque for each segment. 4. Sum the torques for all the segments and determine the whole body center of mass location. 5. Printout your spreadsheet results. Return to the picture you have analyzed and locate where on the image the whole body center of mass is located using the computer image coordinates. Mark this point on a printout of the picture. DATA TABLE FOR SEGMENTAL POSITIONS PROXIMAL DISTAL x (cm) y (cm) x (cm) y (cm) LENGTH PERCENT SEGMENT CM x (cm) y (cm) MASS TORQUE PERCENT x (N/m) y (N/m) RIGHT FOOT 50.00% 1.33% LEFT FOOT 50.00% 1.33% RIGHT LEG 41.90% 5.35% LEFT LEG 41.90% 5.35% RIGHT THIGH 42.80% 11.75% LEFT THIGH 42.80% 11.75% RIGHT UPPER ARM 45.80% 2.90% LEFT UPPER ARM 45.80% 2.90% RIGHT FOREARM 43.40% 1.57% LEFT FOREARM 43.40% 1.57% RIGHT HAND 46.80% 0.50% LEFT HAND 46.80% 0.50% HEAD 55.00% 8.20% 50.00% 45.00% LEFT TRUNK RIGHT TRUNK TRUNK 100% SUMMARY Based on your data collection, analysis and results briefly summarize the procedures used to determine whole body center of mass. In addition, discuss the specific image used in the lab and how center of mass relates to such performance. In your summary and discussion, include responses to the following questions. 1. For the body configuration analyzed, was the calculated center of mass position within the volume of the body? Under what configurations would you expect the center of mass not to be within the volume of the body? 2. Was the calculated center of mass position over the base of support in the photo analyzed? Under what conditions does the center of mass have to be over the base of support and when does it not have to be? 3. The process of estimating the center of mass location based on body segment parameters (the segmental masses and locations) introduces some estimation errors into the calculations. What errors were involved in this whole process? Which are the most significant errors? Saint Xavier University Department of Exercise Science Lab Report Template Cover Page • Lab # • Experiment title • Group members • Due date Specific Aims (1 paragraph) This paragraph should state the specific objectives for that experiment. Do not copy directly from the lab manual. Background (1-3 paragraphs) This should describe topics covered in throughout the experiment, specifically covering the basic anatomy and physiology of the system(s) involved for the lab. Also important terms and concepts should be clearly defined. I recommend using your textbook for background material. Copying of the manual will not be accepted. Methods (1-3 paragraphs) Describe the procedure you used to collect your data. Include the equipment and materials used, indication of electrode placement, and specify modifications (esp. type or length of exercise performed by subject). The subject profile should be in this section. This section should give enough information that your experiment could be duplicated. However, it is not necessary to write every part of your procedure down, like turning on the computer. It is alright to assume that you are writing this for a fellow exercise physiology lab student. This should be written in the past tense. Results (1-2 paragraphs) State the results you obtained. You must reproduce ALL data tables from lab sheets in the report. You may cut and paste once the results have been entered into the tables. The results should be stated but not discussed extensively, e.g. heart rate was found to increase after exercise. Be sure to include units in the graphs and tables and also label everything (axes, figures, tables) appropriately. Any required equations/calculated values should be included in this section. Discussion (1-3 pages) Discuss the results of your experiment. What do your results mean? Be sure to reference the relevant exercise physiology in your discussion. What are some of the limitations of the study? What were some possible sources of error specific to your experiment? You must answer ALL of the discussion questions at the end of each lab in this section. The questions should be answered in order and written in paragraph form. Do not format as Q&A. Conclusions (1 paragraph) State the conclusions for this experiment. What was the main result of the experiment? Do not repeat your discussion section here. References All references used should be included in their own section and must be referenced in proper format (APA or AMA). Examples: Schembre, S. M., & Riebe, D. A. (2011). Non-exercise estimation of VO(2)max using the International Physical Activity Questionnaire. Meas Phys Educ Exerc Sci, 15(3), 168-181. Sun, X. G., Hansen, J. E., Ting, H., Chuang, M. L., Stringer, W. W., Adame, D., & Wasserman, K. (2000). Comparison of exercise cardiac output by the Fick principle using oxygen and carbon dioxide. Chest, 118(3), 631-640. General Lab Report Instructions • Reports should be single-spaced and printed on one side of the page. 12 point font, Cambria font with 1 inch margins. • A good report reads like it was the work of one author – proof read it as a group. • Tables should not be split on two pages. The entire table should fit on 1 sheet. • Write in a professional style. • Most of the lab report should be in past tense as it describes work you did. • Figures and drawings (and graphs) – should be given a caption below the image. o If you include images from the web or from a book or a magazine, be sure to cite the source, otherwise it is plagiarism. Best way is to put in the figure caption something like, "Image (or figure) reproduced from .......". If you modify a figure, put, "Figure adapted from ......". If the image is from the web, use the URL as the citation. • Graphs – 2D graphics represent data more realistically than 3D graphics. • Tables – should be number and a title placed above the table. o Any abbreviations or definitions should be below the table.
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I have finished, I repeat that it was a very fast work done, I hope you appreciate it. If you have the opportunity to make modifications more calmly, I will gladly do so. Sorry for the inconvenience but as I mentioned before, it was not my mistake

Lab #2
Center of Mass
Group members
Due date

Specific Aims
Calculate the location of the center of mass of a moving image, using the body segmentation
technique and estimates of the segmental masses, with respect to a reference point

Background
The center of mass of a system of particles is a point that, for many purposes, moves as if it
were a particle of mass equal to the total mass of the system subjected to the resultant of
the forces acting on it. It is used to describe the translational motion of a system of particles.
Anthropometry deals with the quantitative study of the physical characteristics of man and
is a great tool used to obtain the location of the center of mass of eac...


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