Ground reaction forces

Provide easy-to-use, extensible software for modeling, simulating, controlling, and analyzing the neuromusculoskeletal system.
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Samuel Dyson
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Joined: Mon Apr 04, 2011 7:42 pm

Ground reaction forces

Post by Samuel Dyson » Tue Jul 12, 2011 1:41 am

Hi I've been trying to create .mot files for my ground reaction forces. I've been looking at subject01_walk1.mot from the Gait2354 example. I'd just like to clarify what units the ground_force_vx etc are in and where exactly this data came from? Is the C3D file for this example available?

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Yi Wang
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Joined: Fri Oct 30, 2009 1:12 pm

RE: Ground reaction forces

Post by Yi Wang » Thu Jul 14, 2011 10:07 pm

Hi Samuel,

I don't know what exactly software the official team using, but currently I am using Vicon Motus to export the data into C3D file and using a Matlab Toolkit to extract data and transform them into the essential format which OpenSim needed.

You can find the the Matlab Toolkit at the following address,

As for the unit, I am pretty sure for forces the unit is Newton and for COP is "meter" and for the moment is "Newton * Meter".

Correct me if I was wrong about anything.

Yi Wang
University of Utah

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Wenxin Niu
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Joined: Sun May 22, 2011 5:23 am

RE: Ground reaction forces

Post by Wenxin Niu » Fri Jul 15, 2011 4:37 am


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Sangjun Lee
Posts: 30
Joined: Sun Apr 24, 2011 10:30 pm

Re: Ground reaction forces

Post by Sangjun Lee » Tue Sep 20, 2011 10:34 pm

Hi all,

If you use VICON motion capture systems,
please try our toolbox which directly converts VICON motion capture data(*.csv) into OpenSim inputs(*.trc and *.mot).
This is much easier and faster than converting C3D files.

Please refer to our project page:
The toolbox v.1.4.1 is already available, but the user manual is now in preparation.
If you have any questions in using our toolbox, please contact us.


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Lauren Ferris
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Joined: Wed Sep 12, 2012 2:09 pm

Re: Ground reaction forces

Post by Lauren Ferris » Thu Sep 13, 2012 12:09 pm

I am new to this opensim thing but I had a question about the units. We measured in N and mm so would I need to convert that before using the c3d converter?