Opensim 1 Answer Sheet PDF

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Opensim Assignment 1 Answers for Dr. Reinbolt...

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ANSWER SHEET OpenSim Tutorial #1 Introduction to Musculoskeletal Modeling 1. Degrees of Freedom a. How many degrees of freedom does the model have? 14 b. Which motions have been simplified? Which motions have not been modeled at all? the model doesn’t take into account the variation of flexibility among people so all motions have been simplified particularly the hip adduction and abduction. Rotations also are not shown as a degree of freedom here. c. How many muscles are in the model? Is this greater than the number of degrees of freedom? What is the minimum number of muscles required to fully actuate the model? Hint: Full actuation of the knee, for example, means both knee flexion and knee extension. There are 77 muscles in the model (not counting a muscle that was represented more than once like GMAX 1,2,& 3). 2. Muscle Paths a. Name two other muscles in the model that are represented with multiple lines of action. Why do you think these muscles are represented in this way? The GMAX and the LGMED are also shown this way They are shown this way because the different lines of action impact different parts of the body. Representing the whole muscle as one line of action would not be accurate. b. Which knee extensor muscles have wrapping points? At what knee angle do they occur? The Vastus Lateralis has wrapping points at -70 deg, 110 deg Vastus Medialis has wrapping points at a knee angle of -70 deg, -102 deg, The Vastus Intermedius begins to wrap at a knee angle of -82deg The Rectus Femoris begins to wrap at a knee angle of -84 deg 3. Modeling Limitations Do you see any problems with GMAX3? In what ways are point-to-point representations of muscle paths a simplification of musculoskeletal geometry? When the hip is fully flexed the Gluteus Maximus 3 muscle is shown going through the bone. The pt-to-pt representation of muscle geometry fails because the muscles are much more flexible than this simple model.

4. Muscle Fiber Length vs. Joint Angle a. Study the plot of muscle fiber length vs. knee angle. Do you think these curves would look different if, for example, the right hip was flexed? YES b. Compare the two sets of curves you have just plotted. How have the curves changed? Can you explain your findings? How can bi-articular muscles complicate analysis? Yes the Vastus Intermedius remained the same, but the Rectus Femoris curve has a much shorter fiber-length when the hip is flexed. This is because in order for the hip to flex and the leg be raised this muscle must tighten thus shortening its fiber length. Bi-articular muscles complicate analysis because they cross two joints. Their function is more complex because it often depends on their anatomy and the activity of the surrounding muscles of the joint. 5. Muscle Moment Arm vs. Joint Angle Study the plot of knee extension moment arm vs. knee angle for rectus femoris and vastus intermedius. At what knee angles do the moment arms peak? What are the peak moment arms? The RF curve peaks at a knee angle of -25degrees with a moment arm of .05 The VASINT peaks at a knee angle of -5 degrees with a moment arm of .046 At what knee angle does the discontinuity occur? What do you think causes this? Hint: Look at Question 2.bOpenSim: Intro to Musculoskeletal Modeling Page 3 Discontinuity occurs at about a knee angle of -80 deg this is because the wrapping of the Rectus Femoris and the Vastus Intermedius begins to wrap at a knee to occur at this angle. 6. Range of Motion What differences do you observe? The crouch gait’s leg never fully extends upon heel strike and the knee never flexes back during toe off, The feet move out around the body, knees pull to the inside and the hips have much more rotation.

Identify the intervals at which heel strike, stance, toe off, and swing phase occur for a “normal” gait cycle?

What is the “normal” range of knee flexion during stance phase? How does this knee flexion curve for crouch gait compare to the normal gait data? the normal range of knee flexion ranges from about -3 to -13 the stance phase for crouch gait has an extremely high angle (bent knee) and does not have much variation

7. Hamstrings Length Study the curves. Based on the plot, what recommendation would you give the surgeon? Can you think of any limitations of your analysis? From examining the curve and the model, I would recommend the surgeon relax the hamstrings to decrease the knee angle. The limitations in this analysis are that we are not diving into what exactly what is causing this extreme angle and the forces acting on the muscles should be analyzed to know exactly what is causing this. Also, this model is not tailored to a specific person, just a particular condition. It would be better to analyze the actual person experiencing this crouch gait....