Calculating excitation from activation

[Hoon Kim]

Dear OpenSim users and developers,

Hello, I am trying to calculate the excitation of each muscle from the known activation of each muscle in GAIT2392 (Thelen Muscle Model).
In other words, I want to control each muscle with excitation as an input to get the known activation.

In order to get the known activation using Forward Dynamics, I think this can be done by putting the known activation as an input with ignore_activation_dynamic in Millard Muscle Model. However, the option of ignore_activation_dynamic is not implemented in the Thelen Muscle Model. So, I would like to calculate the excitation by integrating the First-order muscle activation dynamic equation from an article (Thelen, 2003).

If somebody has done this way, could you help me with this calculation? It would be very helpful for me to continue my research.
Thank you so much for any comments and help.

Sincerely,

Hoon

[Dimitar Stanev]

Maybe you can try using the most recent version of the gait model developed by Rajagopal:

https://simtk.org/projects/full_body

The model uses a Millard muscle model so you can disable activation dynamics

[Hoon Kim]

Hello, Dimitar.

Thank you for your comment.
I tried to use the model developed by Rajagopal. That model worked.
But, I am still wondering if the Thelen model can be controlled to act like the Millard model with "disable activation dynamics".
Thank you so much for your comment, always.
Have a great day.

Sincerely,

Hoon

[Thomas Uchida]

I am still wondering if the Thelen model can be controlled to act like the Millard model with "disable activation dynamics".

There is no option to disable activation dynamics in the Thelen2003Muscle model. The Thelen2003Muscle class inherits the "ignore_activation_dynamics" property from the Muscle class, but that condition is not implemented in Thelen2003Muscle.