simtk.org

Hi everyone,

I've tried to do a static optimization with a motion file in order to see muscles activations e forces,
then to verify if they should be reasonable I've done a forward dynamic simulation given as input the results (control.sto) obtained with SO, but it doesn't reproduce the original motion. Why?

Thanks

Maurice

Hi Maurice,

I think that the SO tool should not be used on its own, since it does not consider the system's evolution in time. But for the skeleton to be in a given position, the previous muscle activations matter a lot. The SO is however called by the CMC, one time step at a time. Then, the CMC handles time integration on top of it. Examples of control-driven simulations usually use the CMC's output as input. When you will be using Forward Dynamics, make sure to double check the initial position of your system, as results will vary dramatically otherwise.

Pierre

Thank you for your reply!

So if I want to perform a muscle driven simulation as input for the forward dynamic I have to use the results from CMC.
But if I perform a CMC or a SO on the same problem the results are very different between them
also because SO resolves step by step while CMC integrating over time...
so how can I evaluate my results without having info from EMG, which one are more correct, from SO or CMC? Maybe if my motion is rapid it's better CMC ?

Maurice

So if I want to perform a muscle driven simulation as input for the forward dynamic I have to use the results from CMC.

yes.

But if I perform a CMC or a SO on the same problem the results are very different between them

They are different analysis, so of course, they would give different answers.

so how can I evaluate my results without having info from EMG, which one are more correct, from SO or CMC? Maybe if my motion is rapid it's better CMC ?

Give this a read; http://nmbl.stanford.edu/publications/pdf/Hicks2015.pdf