Scaling-Marker Registration

[Hamed Shahidian]

Hi there,

I was trying to optimize scaling of my model using tricks mentioned in Opensim webinar. However, I encountered couple of questions which I should ask.

In the webinar, it was mentioned that marker registration should be used to match tracking markers on the generic model with the experimental data. For this purpose, I did the following steps:

1. I scaled my model based on suggested scale factors and saved it as Test.osim
2. I ran IK on the scaled model and saved the model after running the IK as Test2.osim
3. I scaled Test2.osim one more time and saved re-scaled model as Test3.osim.

Could you please tell me whether I did a true job for marker registration and scaling or not?

The results of my last scaling were:
total squared error = 0.00838801, marker error: RMS=0.0139667, max=0.0345116 (LKNEMED)

Once I looked at the scaled model, I found that there were small gaps between experimental and generic markers for lateral knee, medial knee, lateral ankle, medial ankle and C7. As we should not move anatomic markers, could you please tell me in what way I can improve my scaling to have errors within the range?

Adding to that, I have couple of questions about scale factors:

- What could be the best scale factor for talus?
- Should we use suggested scale factors in the webinar for the foot segment to scale calcaneus and toe or not?

I have attached my models as well.

Thanks
Hamed

[Hamed Shahidian]

Hi there,

I have asked this my question about 30 days ago, but I have not received any response. Is anyone to help????????

[Thomas Uchida]

Could you please tell me whether I did a true job for marker registration and scaling or not?

This is not an easy question to answer in general: it depends on how you will be using the model, it requires running tests and validating the variables in which you are interested, etc. Furthermore, low marker error does not necessary mean that the model will be adequate for your study. You may wish to consult the following paper for background on model validation: Hicks, J.L., Uchida, T.K., Seth, A., Rajagopal, A., Delp, S.L. Is my model good enough? Best practices for verification and validation of musculoskeletal models and simulations of movement. ASME Journal of Biomechanical Engineering 137(2):020905, 2015 (https://nmbl.stanford.edu/publications/ ... ks2015.pdf).