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Hi everybody,

I am trying to understand the performance of the 'total fiber-force' of different muscles.
I've observed, by OpenSim Plotter, that the 'total fiber-force' of a muscle completely changes if I select as X-Quantity the CMC output "*_states.sto" file instead of the CMC output "*_Kinematics_q.sto" file.
I think I'm plotting the same parameter (total fiber-force), but it's not like this because the two trends are completely different!

I'd like to plot muscle force as a function of time, but I don't understand which one I must consider. Could you help me?

Thanks very much!

Best regards,
Cosimo

Hi Cosimo,
Are you sure you are plotting the total fiber-force by calling CMC output "*_states.sto" file? Because usually "*_states.sto" files contain information about the state variables of your system (i.e. joint angles, muscle fiber lengths, muscle activation..), whereas "*_Kinematics_q.sto" contain kinematic information (i.g. join angles). However, you have to include a report/analysis of the dynamic information (i.e. muscle forces) in your .xml setting file(s). Pay attention to what you are plotting, there is a difference between the fiber force and the fiber force along tendon which has to do with the definition of the pennation angle.

I think the discussion in the following link could be interesting for you:
https://simtk.org/forums/viewtopic.php?f=91&t=4892

Best,
Ali

Hi Ali,
thanks a lot for your help!

I'm plotting the total fiber-force from the OpenSim Plotter, obtaining different results depending on what I select as X-Quantity.
Particularly, you can see the two plots obtained selecting as X-Quantity the CMC output "*_Kinematics_q.sto" and the CMC output "*_states.sto" file looking at the message attachments.
What do you think about?

Thanks very much!

Best regards,
Cosimo Aloisi

Hi Cosimo,

Its a bit confusing but the way you are plotting these values are incorrect. The result of your actions is ploting the fibre-force of the model, NOT the force that the CMC analysis produced.

CMC outputs the actuator force, power and speed. You will be able to access those and plot as a function of time.

Hope that helps,
-james

Hi James,
thanks a lot for your precious help!

I know it's a bit confusing, now I try to explain better.
I need to plot the force of the quadriceps (is it the fibre-force of the model or the actuator force outputed from the CMC?)!
So I don't know if I must refer to the first graph (when I select the CMC output "*_states.sto" as X-Quantity) or to the second one (when I select the CMC output "*_Kinematics_q.sto" as X-Quantity).
You wrote to me of consider the second one, that I observe it's the same plot obtained selecting as X-Quantity the IK output "*_ik.mot" file.
In this case I don't need to execute the CMC tool to obtain the force of quadriceps!
Isn't it strange (I would get the force of quadriceps without consider the force input file "*_grf.mot", because the IK tool doesn't consider it)?

Sorry for the confusion and thanks very much again!!!

Best regards,
Cosimo Aloisi

Cosimo,

Neither of the figures you posted are correct. Plotting fiber-force VS a loaded motion or states file will give you the results from your CMC simulation.

During the CMC analysis there will be files generated with the word 'Actuation' in them (ie subject01_walk1_Actuation_force.sto). This file contains the forces that the muscles in your model produced during the CMC simulation.

The CMC page that describes the output files from the Analysis http://simtk-confluence.stanford.edu:80 ... MC-Outputs

Cheers,
-james

Hi James,

By plotting the quad_fem force (that is a column of the CMC output file "*_Actuation_force.sto") as a function of time, I obtain the same figure got selecting the CMC output "*_states.sto" as X-Quantity (the first figure above).

I'm analyzing the movement of the squatjump and I don't know how read this figure because it's quite "noisy" (is it possible?), while maybe the second figure above (what does it represent precisely?) would be more reasonable. What do you think about?
Thanks very much!

Best regards,
Cosimo Aloisi