This work describes an interactive system for the independent adjustment and definition of multiple degree-of-freedom linkage systems representative of human leg and arm motion. The system is built so that, once the kinematic structure is defined, control points for interactive definition of muscle and tendon parameters may also be adjusted and defined, thus providing interactive, 3D musculoskeletal modeling and simulation. Other applications include medical education, computer aided surgical planning and computer aided prosthesis design.All kinematic transformation nodes are built as linkages within an openGL hierarchical structure. The structure for independent adjustment of each axis of motion required tracking the inverse of all transformations applied to the axis during visualization and adjustment. The inverse is applied to all structures below the axis of interest so that only the axis is affected during 3D adjustment. The result is a kinematic structure definition program with which the user interactively builds the kinematic model. The program provides unlimited rotational degrees of freedom and the definition of linear and curve path models for all skeletal muscle/tendon units.