Assistive forces as external forces

[Sivaprasad Kunnath]

Hi,

I am simulating an experiment with an assistive force as rehabilitative learning effort applied to a point on the wrist. This force produce the movement to the arm. I am curious on how to model the force. At present, I have the force to be a constant time series force. I want to know whether for the purpose of inverse dynamics and finding muscle activation using Moco, I can assume this assistive force to be the external force file.

I am confused at this point, as I have read that for the outcome of the experiment to be precise ( calculation of joint forces, torques and muscle activations and forces) an external force applied to the body grounded is essential to calculate the inverse dynamics using the closed chain newton-euler equations. However, I also saw some discussions in the forum, where it said it was okay to assume the perturbation forces as external forces. If that's the case, should I model this force to be applied on the wrist or provide an external force (like the grf data) on the grounded body and apply a point force on the wrist on it's frame. Thanks for the help.

Regards,
Siva

[Carmichael Ong]

An external force does not always need to be applied to bodies that interact with the ground. Many people use simulations for gait, so this is often what is done, but if a force interacts with the upper body, it makes sense to apply it to the correct body (e.g., upper arm, arm, hand).