The .sto file format was created by the developers of OpenSim. It is very similar to the .mot file format, with two main differences:

  • The time values in the time column of a .sto file do not have to be uniformly spaced
  • The first column of a .sto file must contain time, whereas a .mot file can contain other quantities in the first column

There is only one format for the header of a .sto file and it is very simple, as shown below:


The first line contains the name with which the .sto file will be referred to when it is loaded into OpenSim. The second line is nRows= followed by the number of rows of data in the .sto file. The third line is nColumns= followed by the number of columns of data in the .sto file (including the time column). The last line is endheader. Immediately following the endheader line is the data section of the .sto file, which is identical to the data section of a .mot file, except that the time column is allowed to have non-uniform spacing.

Example .sto files, such as subject01_walk1_RRA_Actuation_force.sto, are provided in the examples/Gait2354_Simbody/OutputReference/ResultsRRA directory, which is part of the OpenSim distribution. As of version 2.3.2, the sto files have a header that includes:

  • Version number (version=1)
  • Whether angular data specified in the file are in radians or degrees (inDegrees=yes/no). OpenSim would assume that old sto files are in radians, if this is not the case you can manually change this flag in the file or use the Help->Convert Files option to set it.