Muscle recruitment, GRF prediction and force plate

I have several questions about muscle recruitment, GRF prediction and force plates.

1: In one of the tutorials it has been mentioned that the default muscle recruitment in AnyBody is Polynomial (power=3) I would like to know
if that is using UpperBound OFF or ON? (In the Mocap example, the UpperBound has been to OFF)

2: I use GRF prediction for my study since I dont have any kinetic data, I wonder what would be the optimal value for strength parameter in GRF prediction example?

2 a): How much of a difference does it make when the strength increases or decreases??

3: When using GRF prediction and Polynomial muscle recruitment (power=3) UpperBound ON, The following error will be produced
in most of the trials; "“Muscle recruitment solver : solver aborted due to singular KKT matrix”. However, the ID results (e.g. Muscle activation, joint forces) will be produced.
When I turn the UpperBound OFF there wont be such an error HOWEVER, the ID results are different in terms of magnitude and sometimes pattern compared to when the UpperBound is ON.

3 a) I would like to know which one is the most appropriate approach especially if muscle synergy is the focus of study?

4: In a separate study I have obtained some Mocap data with Kinetic information from two force plates. however,
I assume in order to obtain correct ID results (e.g. Muscle activation, joint forces) we require having three force plates but I have seen in many papers only two force plates were used? I know in OpenSim the model fails but I dont know if this is also the case in AnyBody?

5: When is it appropriate to add extra drivers to your model?
lets say If we have enough markers on the scapula, clavicle, do I need to Turn ON the SCmarkers?

Thank you in advance for your response.

Dear Pouyan Mehryar,

I will assume that you have read the following PDF file for GRF prediction:

  1. For your question, you should always check the following value in your AnyBodyStudy object by yourself.

  2. It is hard to answer your question here because we don’t have the full information of your model. And everyone has different environment.
    I would recommend you to perform some parameter study of GRF prediction model compared by the real measurement in order to find the best set of those GRF prediction parameters for your experimental environment.

  3. I would recommend you to set this ‘UpperBoundOnOff’ option as ‘On’.
    The reason is that there are some AnyGeneralMuscle objects which will provide the pelvis residual forces and moments. And the strength of these AnyGeneralMuscles are very small in order not to activate them too much.
    So if you set this ‘UpperBoundOnOff’ option as ‘Off’, then these AnyGeneralMuscles can’t be overloaded. In that case, the inverse dynamics of the model may fail.

  4. There is no special reason why the model which has three force plates is easy to fail in AnyBody.

  5. If you have enough number of markers, then you don’t need to add extra drivers in general. These extra drivers are only needed when you don’t have enough number of markers to drive the full kinematics of the human model.

I hope that this may be helpful to you.

Best regards,