Can I use Analyze tool to get muscle forces?

[Hari S]

Hello.
I was using analyze(Force reporter, JointReaction) to find the muscle forces and joint reactions for a particular motion. But the values I get are a bit big. (around 30,000) What is the reason behind it? How can I get this result in N.
Also, where can I find details about the output files? The terms are a bit confusing for me.(fx,mx,px)
Thank you.

[Dimitar Stanev]

You need to run Static Optimization to find the muscle forces.

If you get large forces you need to verify that the motion is correct and that you don't apply large forces to the bodies. Also it is possible that the motion file is in degrees and the header is in rad (inDegrees=false). You can check this by performing inverse dynamics.

There is nothing confusing about fx = force in x-dir, mx = moment in x-dir and px is the point (x-dir) where the force is applied. Also you know how these measurements are expressed from the naming convention. Read the documentation and you will not get confused:

http://simtk-confluence.stanford.edu:80 ... s+Analysis

[Hari S]

Thank you.
What does 'MuscleAnalysis_Active Fiber Force' file contains? I got this as a result from the analyze tool.
Thank you

[Thomas Uchida]

What does 'MuscleAnalysis_Active Fiber Force' file contains?

The file contains the active fiber force for each muscle in the model. The "active fiber force" is the portion of the fiber force that is a function of activation (see https://simtk.org/api_docs/opensim/api_ ... ml#details).

{active fiber force} = {peak isometric force} * activation * {coefficient from active force–length curve} * {coefficient from force–velocity curve}