Analyze tool

[Zhen Yang]

There are two ways of doing analyze tool.
One using controls, and the other one using motion. And I got different results from them, so I wonder what are the diffrences regarding output file of these two methods?

[Zhen Yang]

and when using Analyze tool to compute hip joint reaction force, I get forces in x-, y- and z-direction.

Which coordinate system do these force components belong to? Global coordinates system in the room or the local one around the hip?

[Zhen Yang]

Hi,

I have figured out about coordinate system after reading the document about analyze tool, but I still have no clue about difference between using controls and motion.

Can someone help me?
Thanks.

[Ayman Habib]

Hi Zehn,

The specification of motion and control are basically orthogonal/unrelated. Normally you use the AnalyzeTool to analyze a trajectory provided as a motion. You may or may-not decide to apply a set of controls to the muscles and/or actuators while doing the analysis. Specially important when you're analyzing a model with muscles, the muscles behavior is completely dependent on whether you provide specific controls or if you allow them to equilibrate. If you are running an analysis on the results of an existing simulation, you will most often specify a set of controls and states output by that simulation. Please consult the documentation page here
http://simtk-confluence.stanford.edu:80 ... lysis+Tool

and let us know if you continue to have questions.

Best regards,
-Ayman

[Zhen Yang]

Hi Ayman,

thanks for your reply. I have read the documentation about analyze tool, and I am still comfused.

I used model Gait2392 and did scaling, IK, ID, RRA and CMC. When I used analyze tool "Joint Reaction" to obtain hip contact force, I did it in two ways.

1. I used controls and states from CMC result, check the equilibrium box
2. I used only motion file from IK result, without checking the equilibrium box

and I got different values, so my question is what is the difference between these two? My guess is that using controls and states from CMC, the analyze results take muscle forces into account, and when using only motion file, no muscles are activated and analyze results come only from external forces, in my case, ground reaction force.

Is this correct?

[abeer mohamed]

Hi Zhen
from your posted message I realized that you have run scaling, IK, Inverse dynamic, RRA, and CMC. I have some difficulties running RRA, it may be because of my grf.xml file. so my question is how you created your grf.xml file. did you use the existed one or create your own.
thanks
abeer

[Matt DeMers]

You should not equilibrate muscles. If you've performed CMC, you already have all trajectories of the muscle states (activation, fiber length) and initial conditions for muscle were already equilibrated.

Did you check the JointReaction documentation? http://simtk-confluence.stanford.edu:80 ... s+Analysis

You can not compute joint reaction forces with just kinematics. You need kinematics, all muscle forces, and all externally applied forces to fully compute dynamics and the resulting joint reaction forces. A states file from CMC contains all kinematic states and all muscles states, thus it contains all the information about muscle forces. If you supply a kinematics file instead of a states file, you must supply muscle forces separately. Take a look at the JointReaction documentation, specifically the forces_file property.