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OpenSim is an open source application and tool that allows users to develop, analyze, and visualize models of the musculoskeletal system for various applications (including but not limited to prosthetic design, sports performance analysis, and load analysis). In class, we analyzed examples of 3D models containing bones, muscles, and joints to see the coordination and inner workings of the musculoskeletal system
After opening the 3DGaitModel2392 model in OpenSim, I adjusted the coordinates for specific elements in the musculoskeletal system to position the model in a 'knee-up' pose; particularly, I adjusted the ankle_angle_r value to -64, knee_angle_r to -85.5, and hip_flexion_r to 87. For reference, the model's default position is in anatomical standard position.
| Tutorial 1 |
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.
The model has 23 degrees of freedom (based on the coordinate sliders). Within the right leg of the model (specifically the hip, knee, ankle, and toes), it has 7 degrees of freedom.
hip: 3 degrees of freedom; hip flexion (XZ), hip adduction (YZ), and hip rotation (XY)
knee: 1 degree of freedom; knee angle (XZ)
ankle: 2 degrees of freedom; ankle angle (XZ), subtalar angle (YZ)
toes: 1 degree of freedom; mtp angle (XZ)
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.
The model simplifies the joint motion of the toes by grouping them together. In real life, for example, you would be able to wiggle your big toe individually, allowing for more degrees of freedom.
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-to-point representations of muscle paths a simplification of musculoskeletal geometry?
The glut_max3_r muscle contorts and folds over itself at certain coordinates. This shows the limitations and over-simplification of point-to-point representations of muscle paths.
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?
Observing the muscle fiber length vs. the knee angle using OpenSim's plotting mechanism, I would expect the fiber-length values for the rectus femoris to be lower if the right hip was flexed. This is because the rectus femoris is directly attached to the right hip, and as a result of an angle change, they would be contracting and changing in length.
fiber-length vs. knee angle when the right hip flexion is 45 degrees
fiber-length vs. knee angle comparison between default pose and when the right hip flexion is 45 degrees
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 curve for the rectus femoris rectus has changed, experiencing lower values for fiber length overall as the angle value increases. On the other hand, the vastus intermedius is attached to the right thigh, so its values aren't changing as the hip flexion angle increases. Bi-articular muscles complicate analysis because they involve two muscles crossing, yet they influence the movement of two different joints (in this case, the rect. fem. on the hip and the vast. int. on the thigh)
model with a right hip flexion of 45 degrees
6. Range of Motion
To begin simulating movement with the model, I moved the 3DGaitModel2392 back to its default position, before loading the movement file by going from file > load motion > normal.mot. This contains the kinematics for a normal gait. Then, I loaded the same model, changing the motion file to crouch1.mot
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. Now quantitatively compare knee flexion angles over the crouch and normal gait cycles.
in the normal gait, the knee angle changes significantly, experiencing a larger drop in the angle around .7 seconds; it starts at ~-5 degrees. Contrarily, the crouch gait experiences less significant changes in the knee angle, and it starts at ~-60 degrees. In other words, the knee flexion range of motion for the normal gait is bigger than the range of motion for the crouch gait.
opensim_video.webm
b. 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.
c. What is the range of motion for knee flexion during stance phase for normal gait?
The range of motion for the knee flexion during the stance phase for normal gait is 20 degrees.
d. How does knee flexion range of motion for crouch gait compare to that of normal gait?
the range of motion for the knee flexion during the stance phase for crouch gait is ~6-7 degrees, which is significantly lower than the RoM for normal gait.
| Tutorial 2 |
2. Musculoskeletal Model of the Wrist
definition: Radial deviation is defined as wrist motion towards the radius bone, or thumb side. Wrist flexion is the wrist motion that faces the palm towards the forearm, while wrist extension faces the palm away from the forearm.
Which motion is expressed in positive angles: wrist flexion is wrist extension?
Flexion is the opposite of extension.
The wrist extension is expressed in positive angles, while the wrist flexion is expressed in negative angles.
Which motion is expressed in positive angles: radial deviation or ulnar deviation?
ulnar deviation is expressed as a positive angle, while radial deviation is expressed as a negative angle
3. What are the functions of the Extensor Carpi Ulnaris (ECU) muscle?
the Extensor Carpi Ulnaris deals with ulnar deviation
4. What are the functions of the Extensor Carpi Radialis Brevis (ECRB)?
The Extensor Carpi Radialis Brevis deals with radial deviation
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