Opensim教程1-肌肉骨骼建模入门
声明：
本文仅代表作者自己观点，对数据和叙述的真实性无法保证。
Question:
脑瘫患者走路时会出现蹲着走的状态，运动学上的反应是：膝关节过度屈曲，髋关节大幅度的屈曲和内旋。
假设：腘绳肌变短是造成这种步态的原因。那么现有的解决方案是：通过手术延长腘绳肌。然而延长腘绳肌可能会解决问题，也可能会带来其他问题。
问：是否应该对患者实施该手术？
作业：
1.Degree 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.
23个自由度。右腿有7个自由度
（hip rotation R, abduction R, and flexion R）3
knee angle R
Ankle angle R
Subtalar angle R
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.
opensim中的自由度是经过简化的，比如膝关节看似只有屈伸的自由度，但其实还有内外旋和内外翻的自由度，但是比较小。另外，对于有些自由度，比如膝关节，并不是所有的受试者都能做到该自由度，因此需要对特定受试者的自由度进行限制和增加。
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?
答：模型中有92块肌肉。肌肉数目多于自由度数目是为了更真实地模拟人体的复杂性。在现实中，很多关节是由多块肌肉共同驱动的。理论上，为了完全驱动一个模型，所需的最少肌肉数目应该等于模型的自由度数。但这只是理论上的最小值。在实际应用中，由于人体的复杂性，通常需要更多的肌肉来确保模型的稳定性和准确性。
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?
答：比如股四头肌：股直肌，股内外和中间肌。单个线条并不能反应股四的全部特征，增加了模拟的准确性。
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.
答：股内侧肌大概在膝关节弯曲70°时候出现，避免肌肉直接穿过固定的解剖结构。当该肌肉出现wrapping points时，股直肌并未出现。
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?
答：
glut_max3_r肌肉路径的问题:
在某些关节角度下，肌肉路径可能会"穿透"骨骼或其他结构，而不是真实地围绕它们。这种穿透现象可能会导致模拟结果的不准确。
在某些关节运动范围内，肌肉的路径可能会变得不自然或不合理，尤其是在极端的关节角度下。另外还是约束的问题需要注意。
点对点肌肉路径表示的简化:
几何简化: 点对点的肌肉路径表示忽略了肌肉在实际解剖中的宽度和厚度，只关注其起始和结束点。这可能导致肌肉路径与实际解剖路径存在偏差。
包裹点的缺失: 在没有包裹点的模型中，肌肉可能会直接穿过骨骼或其他结构，而不是真实地围绕它们。包裹点的引入可以改善这个问题，但仍然是一种简化。
功能简化: 点对点的表示方法可能不考虑肌肉在不同关节角度下的力学特性变化，如力-长度关系和力-速度关系的变化。
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?
答：
如果hip felxion angle发生了变化，
股直接的曲线也会发生变化，因为股直接是跨关节肌，肌纤维的近侧端随着骨盆的前后倾发生了改变。
而vas_int_r变化的可能性较小，然而仍然可能被轻微影响。
b. In the Coordinates window, adjust the model's right hip flexion to 45 degrees(save the pose asr_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?
Note: To select multiple curve names, hold down Ctrl (PC) or Command (Mac) while selecting. To print or save a plot, right-click on the plot and select Print or Export Image.
答：
vas_int_r的曲线并未发生变化，股直肌肌纤维长度整体下移。由于髋关节屈曲导致肌纤维长度被预拉长。
5. Muscle Moment Arm vs. Joint Angle
答：
a.What are the peak moment arms for each muscle and at what knee angle do they occur?
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? Hint: Look at Question 2.c
答：由于wrapping point的存在。
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
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.
注：这里没有event时间的添加，使用测力台或者运动学数据对步态周期进行判断，需要查看原始数据。
c.What is the range of motion for knee flexion during stance phase for normal gait?
答：大概在20°。
d.How does knee flexion range of motion for crouch gait compare to that of normal gait?
答：10°左右。
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 hamstrings lengthening surgery?
答：峰值长度缩短了。延长肌肉，有可能使患者恢复到更正常的步态。但带来的后续情况需要更多的科学研究来确定。决策并不容易。
b.What are some limitations of your analysis?
答：改变肌肉的长度带来的负面影响还不清楚，需要更多的研究来确认。
8. Additional Crouch Gait Files
略
