Inverse Dynamics Using a single force plate

[Caitlin Edgar]

HI there,

I am currently struggling with my inverse dynamics process using a typical able-bodied model.

I have force plate data for only one force plate and marker data for a full stride.

My inverse kinematics are complete and look to be correct.

I have checked all of my units and made sure they are the same for all input files but when I try and carry out my ID I get weird results tending towards huge numbers. (images attached below).

I have tried with a single leg model in case there is an impact with only having one force plate, but it makes no difference to the results.

The force vector looks to be acting in the correct place on the model on the right calcaneus

Please can someone help to understand where the issue is?

Thank you!
Caitlin

[Mohammadreza Rezaie]

Hi Caitlin,

The issue might be how the GRF is applied to the foot segment.

https://simtk-confluence.stanford.edu:8 ... cification

Is it assigned correctly?

[Caitlin Edgar]

Hi Mohammadreza,

Thank you for your reply.

I have a feeling it is something to do with the application but I have the exact same settings as in the link you attached and I am using the same model I have for other simulations which have worked.

Any other advice would be greatly appreciated as I am still stuck on this.

Thanks!

[Mohammadreza Rezaie]

Hi, I suggest you set the time range exactly according to the foot contact (stance phase of gait) and see the output. The high values in joint moment might be the artifact of the filtering in ID tool. I can check if you share your data (e.g., the scaled model, IK output, force file).

[Caitlin Edgar]

Hi Mohammadreza,

Thank for you reply, I have tried in the stance phase however this is also not working.

I have shared my model and all the required data here.

The original data was received in a matlab structure.

I created trc and mot files from this structure.

The original model is scaled from one available on opensim.

The IK files are also attached.

Please let me know if you need any other files.

Any insight into this problem would be amazing, thank you for your help.

Caitlin

[Mohammadreza Rezaie]

Thanks for sharing. The problems is that the time range in [26_walk_1_ik.mot] file is [2.91, 3.76] but the time range in your [subject_26_walking_1_2.mot] file is [2.91, 3.41] and you have nothing for the rest. This is the source of the issue. Two suggestions:
1. set the time range according to your external load file, i.e. [2.91, 3.41];
2. set zeros for the rest of your external load file (it is preferable).

id.png (26.15 KiB) Viewed 355 times

Hope this helps.
-Mohammadreza

[Caitlin Edgar]

Thank you sooo much!

This has actually been a life saver. I have tried it on mine and got the same results as you.

Thank you!
Caitlin