SIMM allows users to build models that accurately represent force generation of muscles, geometry of bones, kinematics of joints, and dynamics of movement. In SIMM, a model consists of a set of rigid segments that are connected by joints. Muscles and ligaments span the joints, develop force, and generate moments about the joints.

The software loads a model by reading a set of bone files, a joint file, and a muscle file. The "File Loader" scans these input files and creates a data structure that represents the musculoskeletal model. Once loaded, a model can be edited and analyzed with a number of graphical tools. For example, a "Muscle Editor" allows users to change the line of action and force-generating properties of a muscle. A "Plot Maker" calculates the lengths and moment arms of muscles in the model, enabling users to analyze the functions of muscles for a range of body positions. Also, given muscle activations, the force and moments that each muscle generates can be computed. Body motions measured during a movement may be read into the software to animate a model or to evaluate simulation results. When the software is used in connection with a dynamics engine, SD/Fast (Symbolic Dynamics, Mountain View, CA), the joint motions resulting from a pattern of muscle activations can be computed. SIMM is written in C and uses the OpenGL graphics library; it runs on Windows and Silicon Graphics Irix systems, and is available at MusculoGraphics, Inc. Please see the SIMM User's Guide for more details.