Users can upgrade to OpenSim 3.1 from OpenSim 3.0 without any major changes to their models or simulation workflows. A few upgrade notes for users:

1) If you are using Matlab scripting, you will need to re-run the set-up process to direct Matlab to the appropriate libraries for 3.1. See Configuring Matlab for OpenSim.

2) Several objects and functions have been deprecated in OpenSim 3.1. Although the following objects and functions are still available in OpenSim, we advise removing them from your code and workflows since they will be removed in future releases:

3) In the GUI, the option "Preview motion data…" (in the File menu) has been changed to "Preview experimental data…" to reduce confusion with loading motions (.mot or .sto files in the OpenSim format).

4) We made several updates and bug fixes to the Millard muscles, though these updates should have minimal impact on users:

5) The interface to MuscleMetabolicPowerProbeUmberger2010 has evolved during the preparation for the official release of OpenSim 3.1. Users of the metabolic probes in earlier beta releases of the software should load models containing metabolic probes in the OpenSim GUI and resave to update.