Bushing Force stiff AFO

[Shivangi Giri]

Greetings!
I have tried implementing soft and stiff versions of AFO in a OpenSim model, similar to Toylanding example. I have attached two bushing forces at the lateral and medial sides of the AFO (where the cuff and footplate join). I have opened the subtalar angle and now when I simulate walking, I observe that stiff AFO increases the muscle activations of the calf muscles. Now as the stiffness increases, the bushing forces decreases. Is it because of this decrease in the bushing forces that the muscle activations are increasing?
Please note that I have not used any kind of coordinate limit forces. In the ToyLanding example too, the subtalar angle is opened and there are lateral and medial bushing forces and no subtalar coordinate limit force. However, there are limit forces for the knee, but I do not think that is necessary for my study where I am analyzing gait.
Any help would be greatly appreciated.

Regards,
Shivangi

[Carmichael Ong]

Is this a tracking or forward simulation? If it's tracking, it could be helpful to find out what joint torques are needed for the given motion (for both with and without an AFO) to find out if there are additional joint torque requirements that might be driving changes in the muscle forces.