Required additional External Forces needed for MocoInverse

[Adam Park]

Hello Moco Forum,

I am currently trying to design a study looking at the effects of sole stiffness of running gait, and I had a couple of questions about using MocoInverse for such an application;

i) If you were to assume that the bending stiffnesses of each shod condition were known - meaning that the returned elastic torque from the shoe/sole which contributes to the foot's kinetics are given across the trial's full range of motion - then would it be feasible/necessary to add this component as an external force, or an additional actuator, into the inputs for Mocoinverse?

Side note: Of course, I would imagine this would largely depend on the type of joint that the MTP is within the prescribed model (Weld/Pin), so please assume that this would be welded given that the external loads would likely have to be applied exclusively through the calcaneus/rearfoot. I would be largely interested in the muscle/actuator properties attached to the ankle (e.g. gastrocnemius force generation ability, peak active force, negative work, etc.)..

ii) Would it be possible to only use prescribed kinematics and inform the optimizer using processed EMG data (or muscle activations derived from this) without applying any of GRFs as external forces?

Any input at all that could be given would be greatly appreciated - sorry for the lengthy, yet basic nature of the question.
Kind regards,
Adam

[Nicholas Bianco]

Hi Adam,

Yes, you would likely need to add a foot-ground contact force element to your model to model the effects of the shoe/sole stiffness. You will probably need to use MocoTrack or a custom MocoStudy though, since your input kinematics will probably not produce correct forces at the feet "out-of-the-box". Foot-ground contact forces are dependent on the fine kinematics between the foot and the ground, which are typically not captured well with motion capture data.

Best,
Nick