Opensim tutorial 1 answers PDF

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This contains correct answers written by me for OpenSim Tutorial #1....

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OpenSim Tutorial #1 Answers 1. Degrees of Freedom a. Use the Coordinates panel to view the degrees of freedom of the model. How many degrees of freedom, in total, does the model have? List the degrees of freedom of the right leg. There are 23 degrees of freedom in total. It appears that the right leg has seven degrees of freedom, they are: Hip rotation R, abduction R, and flexion R (3), Knee Angle R, Ankle Angle R, Subtalar Angle R, and MTP Angle R. b. All models are approximations. Compare the degrees of freedom in the model to the degrees of freedom in your lower limbs. Give an example of a joint motion in the model that has been simplified. Give an example of a motion that is not included in this model. I count 8 degrees of freedom in each leg compared to the model’s 7 DOF. The additional that isn’t modeled is the movement of toes. It also appears that the model doesn’t account for finger motion – this would arguably add 30 degrees of freedom as every finger would need x, y, and z components assuming all of them were said to move independently. Something that the model fails to account for is individual flexibility constraints – I know I would tear something if I did some of the things the model does, so limits would need to be placed on some movements in order for this to be accurate for a specific person. 2. Muscles

a. How many muscles are in the model? How does this compare to the number of degrees of freedom in the model? 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 28 groups of muscles listed in Navigator ->Muscles. Specifically located in these groups is many more muscles, I counted 76 although I’m not 100% sure about this. Regardless, the number of muscles exceeds the number of degrees of freedom that the model has.

b. Name two muscles, other than the gluteus medius, in the model that are represented by multiple lines of action. Why do you think these muscles are represented in this way? Hint: Other muscles with multiple lines of action use the same naming convention as the gluteus medius. Two muscles are Gluteus Maximus and LG_MED. They are represented by multiple lines of action because their movement affects many other muscles. So one movement of the gluteus maximus may affect one muscle/group of muscles while another movement might affect another group of muscles, etc.

c. Which knee extensor muscles have wrapping points? At what knee angles do the wrapping points appear for each of those knee extensors? A muscle may have more than one wrapping point. ● Vastus Lateralis: -70, 110 degrees ● Vast. Medialis: -70, -102 degrees

● Vast. Intermedius: -82 degrees ● Rectus Femrois: -84 degrees 3. Modeling Limitations a. Zoom in on the right hip, and display only the glut_max3_r muscle (right hip extensors group). Examine this muscle for the full range of hip flexion angles. What problems do you see with the path of glut_max3_r through the range of motion? In what ways are point-topoint representations of muscle paths a simplification of musculoskeletal geometry? There would definitely be a functional problem during hip abduction (ouch!!), particularly in angles exceeding 30-45 degrees depending on the person. I’m not very flexible so anything past 30 degrees would be tough for me in this position. Point-to-point representation doesn’t account for muscle elasticity for dynamic changes that muscles may experience during full range of motion.

4. Muscle Fiber Length vs. Joint Angle a. Study the plot of muscle fiber length vs. knee angle. For each of the rectus femoris and vastus intermedius, do you expect the fiber-length curve be different if the right hip was flexed? Why or why not? I would expect the intermedius to not experience changes during hip abduction, because the motion of it is not inhibited by hip abduction in any way. However, the femoris is closer to the hip, and abducting the hip causes the range of motion to decrease, thus shortening the fiber-length, but not changing the slope of the graph at all. b. In the Coordinates window, adjust the model's right hip flexion to 45 degrees (save the pose as r_hip_flex_45), add rectus femoris and vastus intermedius fiber-length curves for 45º hip flexion. Compare the muscle curves for the model with an unflexed hip you plotted previously to the curves for the model that you just plotted. How have the curves changed? Explain your findings. How can bi-articular muscles complicate analysis?

The curves were just as I expected, the intermedius curve plotted right over top of the original and the femoris fiber-length decreased but the curve still retained it’s original shape. Bi-articular muscles complicate analysis because they cross two joints and therefore affect movement in both of them.

a. What are the peak moment arms for each muscle and at what knee angle do they occur? For the Femoris, the tooltip displayed a max of 0.05 at approximately -22 degrees. For the Intermedius, the max was 0.048 at -0.5 degrees. b. At what knee angle(s) are the moment arm curves not smooth (i.e. have points where the derivative is not continuous)? What do you think causes this? It appears that the curves are not smooth at 82 degrees as well as ~0 degrees. I imagine this is because of the existence of wrapping points in the model. 6. Range of Motion

a. Synchronize and play the normal gait and crouch gait. Be sure to loop the animation, adjust the play speed, and rotate the models. Visually compare the two motions. From your observations, qualitatively describe the general differences in kinematics (joint coordinates) between the normal and crouch gait motions. In the crouching gait, the leg is never fully flexed at the moment that the heel strikes. Similarly, the knee doesn’t fully flex back at the toe off position. Additionally, the crouching gait has more “swing” to it; the hips are forced to rotate more and the hip/knee angles are significantly different than the normal gait. Now quantitatively compare knee flexion angles over the crouch and normal gait cycles. Quantitatively, the crouch gait induces a significantly higher knee angle because how much more the knee has to bend in order to maintain the crouched position. There also is much less variation in knee angle during the crouch gait, for the same reason. c. Draw the plot of the knee angle curve for a normal gait cycle. Label the times at which heel strike and toe-off occur, and the stance and swing intervals. d. What is the range of motion for knee flexion during stance phase for normal gait? By inspection, the range of motion during stance phase for normal gait appears to be between -20 and -2 degrees.

e. How does knee flexion range of motion for crouch gait compare to that of normal gait? For the same reasons as in part b) above, the range of motion during crouch gait is narrower due to the lesser variation in knee flexion. That being known, the angle that the knee is in during crouch gait is much higher than during normal gait. 7. Hamstrings Length a. Study the curves. Based on the plot, how do the peak hamstring lengths in normal and crouch gait compare? For this patient, would you recommend a hamstring lengthening surgery?

Yes, I would recommend a hamstring surgery to attempt to lengthen the muscle, and ideally alleviate some of the tension in the muscles which is undoubtedly causing the crouch gait. The lengthening of the hamstring would decrease the knee angle seen in the plot and hopefully get the patient back to a more normalized gait. b. What are some limitations of your analysis? As the nature of the analysis is simplified, the limitations are obvious. We don’t truly know the specific material properties of the muscles or the specifics behind the forces acting on, in, and around the muscles in question. Before we could confidently recommend surgery, we would need to take a more in depth look at the specifics, such as a specific patient rather than a hypothetical condition....