Question about Y-Quantity Option in Plot

[Phong Phan]

Hi all,

I have a question about Plot in OpenSim. As I read from the tutorial, the proper method to extract the muscle force from a gait simulation is Scaling -> Inverse Kinematics (and Inverse Dynamics) -> Static Optimization. However, in the 'Y-Quantity' in Plot, there are lots of options to choose from (ex: total fiber-force, tendon force, active fiber-force, etc.) to plot force data for selected group of muscle in 'Muscles'. So my questions are:

1) What do these options mean? What unit do they have?
2) It seems that I can draw these fiber-force out using only the IKResults (screenshot attached). Hence, is it considered as a proper method to extract force instead of the aforementioned workflow (Scale ->IK & ID -> SO)?

I'm trying to learn OpenSim so it would be great if anyone could give me some instructions for this problem. Thank you for sharing your time.

[Thomas Uchida]

I think many of your questions are answered in the "Plotting" section of the documentation (https://simtk-confluence.stanford.edu/d ... m/Plotting). Regarding your second question: As stated on the "Curve Creation Panel" page (https://simtk-confluence.stanford.edu/d ... tion+Panel), "For quantities that depend on activation, activation is assumed to equal 1 and equilibrium between fiber and tendon is found. Exceptions are if you use the Activation Override (under Advanced Options) or if you specify an appropriate states file in the X-quantity."