Importing and Exporting SIMM Models

Importing a SIMM Model

Models that were created using Musculographics' SIMM (Software for Interactive Musculoskeletal Modeling) toolkit can be imported into OpenSim.

To import a SIMM model:

Select File → Import SIMM Model… from the OpenSim main menu bar.
The Import SIMM Model window will appear and ask for the following information:
1. The SIMM model to be imported: specify this by clicking the folder icons to select the joint file (.jnt) and muscle file (.msl).
2. The new OpenSim model name: enter the name in the OpenSim file (.osim) textbox.
3. Whether or not a separate XML file for the model markers should be created when the model is imported: to create the XML file, select the check box next to Separate markers file (.xml) and enter a name into the textbox.
After specifying the information in the Import SIMM Model window, click OK.

Be sure to include the extensions when entering file names.

SimmKinematicsEngine models are also supported, provided their base body/segment is called "ground."

To export an OpenSim model as a SIMM model:

Select File → Export SIMM Model… from the OpenSim main menu bar.
From the Export SIMM Model window that appears, click the folder icons to select the location to save the joint file (.jnt) and the muscle file (.msl) for the SIMM model.
When you click the folder icon, a Save dialog box will appear. In this window, enter a name for the file in the File name textbox, and then click Save.
The Save dialog box will close. Then click OK in the Export SIMM Model window.

The SIMM 4.0.1 was used to develop the parsers of jnt and msl files. Accordingly, any new keywords introduced in SIMM afterwards are not supported and should be commented out.
Joints: The set of joints supported by SIMM and those supported by OpenSim are different. This is handled by converting all joints in a SIMM model into "CustomJoint" in OpenSim even though simpler joint types could be possible (e.g. pin, slider).
Muscles: The set of muscle types supported by OpenSim and SIMM are distinct, and each system allows users to add custom MuscleModels. Even in cases where the names indicate similarity, the different implementations will lead to different results. Users should NOT expect to get the same simulations or results running in OpenSim and SIMM. On Import from SIMM to OpenSim, SIMM muscles become Thelen2003Muscle muscles. On Export from OpenSim to SIMM, all muscles become MuscleModel 4.
Only bodies, joints, wrap-objects, and muscles are supported. All other objects will be lost on import/export.