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How can I get out joint angles and loads from a model

Posted: Mon Feb 25, 2019 7:04 am
by vikram_chohan
Hi,

So i have got my own data in which I have scaled the model in OpenSim and set up the inverse kinematics using the gait data i have obtained in a lab using markers. How do i get the joint angles and forces acting in this model?

Thanks in advance!

Re: How can I get out joint angles and loads from a model

Posted: Mon Feb 25, 2019 1:30 pm
by mitkof6
You have to perform an inverse kinematics and inverse dynamics analyses, respectively.

https://simtk-confluence.stanford.edu/d ... Kinematics
https://simtk-confluence.stanford.edu/d ... e+Dynamics

Re: How can I get out joint angles and loads from a model

Posted: Mon Mar 04, 2019 6:04 am
by vikram207
So I have managed to do the inverse kinematics. However I am still struggling with the inverse dynamics. I have got an inverse dynamics file and all i want to find out are forces using opensim. Any further help you can give?

Thanks.

Re: How can I get out joint angles and loads from a model

Posted: Tue Mar 05, 2019 7:40 am
by tkuchida
Inverse Dynamics computes net joint moments. If you're interested in joint loads, you probably want to include the contribution of muscles.

Re: How can I get out joint angles and loads from a model

Posted: Wed Mar 06, 2019 3:16 am
by vikram207
So is there no way to find out the overall force produced from one leg/foot?

Re: How can I get out joint angles and loads from a model

Posted: Wed Mar 06, 2019 3:51 am
by jimmy
Vikram, how can you estimate the joint and muscle forces produced when you don't have ground reaction forces?

Re: How can I get out joint angles and loads from a model

Posted: Wed Mar 06, 2019 4:03 am
by vikram207
With respect to your answer of ground reaction forces, would that just not be x% multiplied by the body weight of the individual? So I need to find the weight of one muscle group(s) in order to get out a round reaction force?

Re: How can I get out joint angles and loads from a model

Posted: Wed Mar 06, 2019 4:37 am
by jimmy
Nope. Without some reaction force, you can't compute useful dynamics. If you want to just guess some forces to make a toy model and analyses, you can do that-- but it would just be that, a toy.

If you didn't collect any force data, there are public data sets that are available that have kinematic and force data. SimTK has walking and running projects.

Re: How can I get out joint angles and loads from a model

Posted: Thu Mar 07, 2019 2:22 am
by vikram207
The force data I obtained via a mot file which was obtained from the gait lab and translated into opensim. No external forces/loads were applied.