Virtual Muscle


Virtual Muscle

Overview
The purpose of this model is to provide an accurate model of muscle, based on experimentally obtained data that can be adapted to any fiber type and can be easily integrated into any existing biomechanical models.  The model has been implemented in MATLAB for two reasons.  The first is that it is a widely used package for modeling systems both at a purely mathematical level using MATLAB alone, and at a hierarchical systems level using a combination of MATLAB and an associated add-on, SIMULINK.

The equations which drive the behavior of this model are outlined in part at the 1998 Society for Neuroscience meeting in Los Angeles, and are elaborated in a series of paper by Brown et al., 1999.  In summary, using a modified Hill-type model, we have been able to account for many phenomenon that have been absent in previous models, including potentiation, length dependence of activation and effective frequency of stimulation, in addition to the basic FL and FV relationships.   Experimental data have been able to provide a specific coefficients for these equations for mammalian fast fatiguable- (FF) and slow-twitch (S) muscle fibers.

The behavior of these two fiber types can be combined with the use of an included recruitment/activation frequency distribution scheme that allows any single muscle created with this system to have an arbitrary number of compartments of any fiber type, with the size of each recruitment group being totally controllable by the user.

For users who do not wish to be involved with the details of muscle fiber properties and muscle compartmentalization, it is simple to take the included data on mammalian FF and S fibers, combine them with muscle specific measures such as mass, fascicle length and tendon length and have a fully functional SIMULINK block which encapsulates the properties of the muscle.  This can be done literally within minutes of downloading the package.

For users who wish a high level of control over the exact workings of the muscle model, it is possible to modify on a coefficient-by-coefficient basis the exact shape of each of the curves associated with the fiber contractile properties.  Further, each muscle can have the size of each recruitment group assigned individually if automatic distribution of compartment sizes is not desired.

Virtual Muscle is a collection of MATLAB m-files, which provide a graphical user interface to allow the user to define and modify muscle fiber types, or else import from an included mammalian muscle fiber database.  Then, whole muscles are created using real masses, fascicle length measures, and so on and each is assigned a number and size of compartments of varying (or all of one) fiber types.  This allows a stand-alone SIMULINK block, containing all the necessary parameters, to be created and inserted into any SIMULINK simulation.  Interfacing with non-SIMULINK packages is possible, such as via DDE on Windows based machines.

Dynamics modeling
Modeling of the dynamics of the system (e.g., joint interactions, bones, etc.) are not handled within the muscle model.  This model was intended only to provide an accurate representation of muscle behavior that could be easily integrated with existing models, or used as a core for the construction of new models.  If your existing dynamics model is in SIMULINK or MATLAB, integration should be straight-forward. Further, any other dynamics packages that can interface with MATLAB or SIMULINK (e.g., through Dynamic Data Exchange [DDE]) can also be used.  A sample application of the use of DDE for Windows 95/98/NT machines is included, using Working Model 2D as the dynamics package.

For those just beginning a simulation, it is recommended that you first investigate the software you intend to use and ensure that it is able to interface with MATLAB.  Whether or not you decide to use our muscle model, the ability to communicate with other packages provides an added level of flexibility should this need arise later in the project.

Validation of Virtual Muscle Model
A validation of the Virtual Muscle model against the data from a feline cauda femoralis preparation is provided here. (Link coming soon.)

System Requirements to Run Virtual Muscle
Virtual Muscle is developed for Matlab running under Windows operating system, but it will run on any platform which supports the following software:

  • MATLAB 5.2 or higher
  • SIMULINK 2.0 or higher
Currently, MATLAB is available for Microsoft Windows, Mac, Linux and other operating systems.

Download
To download the Virtual Muscle files and documentation click here.

Questions/Comments
For questions or comments regarding the Virtual Muscle software, please contact Ian Brown (ianbrown@biomed.queensu.ca) or Gerald E. Loeb (gloeb@usc.edu).


Alfred Mann Institute University of Southern California