This project provides a plugin for OpenSim to simultaneously estimate (external) contact forces and (internal) muscle forces in an inverse dynamic manner from a prescribed motion trajectory.

The plugin implements a custom OpenSim model component to represent a simple point-on-plane contact model. Friction effects are considered according to the static and the dynamic regime of Coulomb’s law. This contact model is evaluated by a special static optimization procedure, that can be run within OpenSim’s Analyze Tool.

We developed this approach to analyze physical interactions between human beings and technical artifacts such as manufacturing machines and sports equipment. However, it is also particularly useful to estimate ground reaction forces during gait.

Background information on this approach can be found in the following publication:

D. Krüger and S. Wartzack, “A contact model to simulate human–artifact interaction based on force optimization: implementation and application to the analysis of a training machine,” Computer Methods in Biomechanics and Biomedical Engineering, pp. 1–10, Oct. 2017.
DOI: 10.1080/10255842.2017.1393804

If you would like to use our work in your own research please cite that paper!


Initial version of the plugin released

Nov 8, 2017

A new file,, has been added to release 1.0 of contactForces.

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