The questions about ID setting files in Version 2.4

[Hang Xu]

Hi, everyone
I have a question about ID setting file in Version 2.4
I noticed that there was a function <forces_to_exclude> in the ID setting file which said "List of forces by individual or grouping name (e.g. All, actuators,muscles, ...) to be excluded when computing model dynamics"
I used the model2392 to test three situations (which changed <force_to_exclude> to ALL or ACTUATORS or MUSCLES) however they all gave me the exactly same output files.
Then I added four knee ligaments (ACL/PCL/MCL/LCL) in model2392 and ran ID step, make the setting file like below:
"<forces_to_exclude> Muscles ACL PCL MCL LCL </forces_to_exclude>"
The joint moments results were all very similar compared with model2392 except for the knee joint moment which was unreasonable large (seem like still include the ligament forces)

so my questions are:
1. why the ID output were exactly same when I changed the content in <force_to_exclude> such as "all" or "muscles" or "actuators" using model 2392?
2. how I can exclude both muscle and ligament force when calculating Inverse Dynamics

Thanks for any suggestion and help.

[Ayman Habib]

Hi Hang,

Normally when you run ID you don't want to include muscles, so the default behavior and files generated by OpenSim exclude Muscles. If your model has other forces for example, ligaments, bushing or contact then you have the option to include or exclude them. For the gait2392 model, it has no Actuators except for muscles so I expect the answer to be identical if you exclude ALL, Muscles, or Actuators.

I don't know if you can mix groups with individual ligaments but you may be able to create a group e.g. "Ligaments" of all ligaments in your model and then exclude Muscles, Ligaments in the setup files.

Hope this helps, and please let me know how that goes,
-Ayman

[Hang Xu]

Hi, Ayman
Thanks for your reply.
I knew that if a model which include only muscle actuators (like model2392),the answer should be identical no matter exclude ALL, Muscles, or Actuators.
So, I tested the ID Results for two different situations using model2392
one like below:
<forces_to_exclude> Muscles </forces_to_exclude>
the other like below:
<forces_to_exclude> med_gas_r lat_gas_r </forces_to_exclude>
I excepted different results since one exclude all the muscles but the other only exclude med_gas_r and lat_gas_r, however, all the joint moment results are exactly same.

Then I tested the ID Results for two different situation using model2392 with ligaments
one like below:
<forces_to_exclude> Muscles </forces_to_exclude>
the other like below:
<forces_to_exclude> All </forces_to_exclude>
I still excepted different results since one exclude only muscles but the other exclude both muscles and ligaments,however, they still gave me the same results for knee joint moments (unreasonable large knee moment compared with model2392 without ligaments)

I also tried to make a group like "ligaments" but I cannot find the corresponding codes in OSIM file.In the GUI, I could see ACL,PCL, MCL and LCL under the list "Force--Other Force".
So, I used the similar code like below:
<ObjectGroup name="L_hip_flex">
<members> add_brev_l add_long_l glut_med1_l glut_min1_l grac_l iliacus_l pect_l psoas_l rect_fem_l sar_l tfl_l </members>
to add the code like below to the model
<ObjectGroup name="Ligaments">
<members> ACL_r PCL_r MCL_r LCL_r</members>
but the ligaments appeared under the list "Forces--Muscles"

So I still have two questions
First, I doubted whether the "exclude force" function works or not. Do you have other methods to test this function?
Second, do you have any ideas about how to create the ligaments group under the list "Forces", like now OpenSim had sublist "Muscles", "Actuators", "Contact Forces" and "other Forces" under "Forces"

Thanks for any help and suggestion