Muscle length modelling software for VICON users

Muscle length modelling software for VICON systems.

This is should allow you to conduct muscle length modelling based on measurements obtained with Plug-in Gait, It includes a Workstation Plug-in and a number of ancillary files to try and smooth the work-flow to view results within Polygon.

There is an introductory report in Polygon format. Download the file and extract to a named folder. Go to the MuscleLengthsReport folder and launch PolygonViewer.exe. The report gives you a good overview of what the software does and what you need to get it running within Workstation (it was written a long time ago). It should work as a PlugInModeller Plug-in in Nexus but you’ll have to work out exactly how to do this yourself.

The underlying model is that posted by Scott Delp on the ISB software repository a long time ago now. I’d always assumed that this was the same as the gait2392 model in OpenSim (both models cite the same references). About a year ago some researchers in Leuven, however, compared the output of this software with that of OpenSim and found differences that would be large enough to affect clinical interpretation. We finally traced the differences to a small number of muscle origins and insertions between the two models. I’ve no real doubt that using either  model consistently (for the same patient and normative reference data) would result in similar clinical conclusions but comparing data from one model with that from the other could be quite mis-leading. Shows you that even two models citing the same references as their source can give different results – you can’t be too careful in modelling.

Polygon 4 handles mesh files differently to Polygon 3 so this report will look quite different (worse) in Polygon 4.

Good luck. Let me know if you have problems.


  1. Hi Dr. Baker,
    I have been trying out this model (actually a modification called MuscleLengthLessPoints.mod, since our lab does not use the SACR marker). I’m able to run the model successfully in Vicon Nexus and extract the muscle lengths.
    Somebody told me that ‘point-to-point’ muscle length models tend to be inaccurate, and a joint angle/moment arm based methods would be more accurate. If I’m correct, MuscleLength.mod implements the latter kind of method? Do you have any comments about the accuracy and reliability?


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