Conditions for the activation of muscles in AnyBody


I uploaded 4 models. All models included the four-bar linkage. It has only 1 degree of freedom.
To drive this model, I classified four different conditions. I assumed that there are two actuators in this system.
It’s obvious an over-actuated system because this system needs only 1 actuator to be driven.

You can see the required torques of the actuators here:

  1. Two AnyReacForce objects
    It is kinetically over-actuated system. So the calculated torque values are very fluctuating.
    I think that AnyBody shows us the one of possible solutions.

  2. Two AnyGeneralMuscle objects
    The calculated torque values are well optimized.

  3. One AnyGeneralMuscle object and one AnyReacForce object
    In this case, AnyGeneralMuscle object was not activated. And I could see the message:
    “The muscles in the model are not loaded due to kinetically over-constrained mechanical system.”

  4. One AnyGeneralMuscle object and one AnyReacForce object with AnyForceConSimpleBound
    In this case, AnyGeneralMuscle can be temporarily activated because AnyReacForce objects has its limits.

Now I’d like to ask of you a question.
Can the muscles in the AnyBody be activated only when there fewer unknown forces than required in the dynamics equations?
In the case 3 above, I might think that the muscle can be activated and the calculated muscle torque can affect the result of AnyReacForce.

I’m sorry if the intention of my question may not be clear.

Best regards,

Hi Moonki,

It is a pity that you cannot be in Aalborg right now. We are running a Ph.D. course on musculoskeletal modeling and have 24 participants from all over the world, and Tuesday and Wednesday were entirely devoted to muscle recruitment issues. Your examples would have been extremely illustrative.

Anyway, you are quite right that the muscles in AnyBody are lazy. They will not work unless they really have to, so if there are driver torques or reaction forces that can do the work, then the muscles will do nothing.

Best regards,

Hi John,

I also think that it would have been a good chance for me if I could visit to Aalborg this week.

And thanks for your reply. I could understand it.

Best regards,