new idea. waiting for others' suggestions and critiques.
muscles are generally modelled as massless lines of action. here we are trying to add weights to the muscle body instead of bundling it th the bony rigid body.
SimTK is maintained through Grant R01GM124443 01A1 from the National Institutes of Health (NIH). It was initially developed as part of the Simbios project funded by the NIH as part of the NIH Roadmap for Medical Research, Grant U54 GM072970.