I am trying to use the MoBL-ARMS upper limb model in OpenSim (version 3.3) to compute muscle forces, and joint torques caused by those muscle forces. Specifically I have measured kinematics (in the form of joint angles) and measured muscle activation (measured EMG which has been processed and normalized to be used as muscle activation in OpenSim), and I need to use those to calculate muscle forces and torques caused by those muscles.
My understanding is that I can do this by using "muscle analysis" in the analyze tool in this way; where q_m, a_m, f_p, and t_p represent respectively; measured joint angles, measured muscle activation, predicted muscle force, and predicted torque:
- Capture.JPG (12.58 KiB) Viewed 248 times
Inputs:
The only way that I have found to use both measured kinematics and muscle activation as inputs is to create a states file that includes both. I have attached a states file I am using as an example. In this case the kinematics are constant but the muscle activation is not because the muscles are resisting against an external torque put on the wrist. Does it make sense to input measured kinematics and muscle activation in this way? It doesn't seem traditional in OpenSim to input measured values in a states file.
Outputs:
The outputs from the muscle analysis include files for muscle forces, moment arms, and moments. My question here is what axis is this moment reported about? For example, one of the outputs is "MuscleAnalysis_Moment_flexion" and its columns look like this:
time ECRL ECRB ECU FCR FCU
0.5 -0.055913554 -0.058456429 -0.152985051 0.057297371 0.300606975
0.505 -0.055939009 -0.058482035 -0.154061918 0.057363028 0.30429875
0.51 -0.055965215 -0.058508395 -0.155120013 0.057425832 0.308007836
First, a time column, then a column for each muscle that contains a torque magnitude at each time step. Am I correct in assuming that these torque magnitudes are about the axis associated with the coordinate "Flexion"? Are the magnitudes given in the other moment files about the axes associated with the coordinate the files are named after?
Hopefully that makes sense.
Thanks for your help!
PS sorry it wouldn't let me upload the states file as a .sto file so it is included as a text file. You will have to make it an .sto file to use it. Also it would not let me upload the geometry folder so the simulations may look strange in the OpenSim view window but should still run just fine.