Reformulation of dynamics equation of planar two-joint arm movements

Presents a reformulation model (RE-model) in which the controller system takes the nature of a limb´s physical design into account to deal with the complex dynamics of planar two-joint arm movements with simple and concise form. The RE-model was formulated based on the dynamics expression for the motion of a single virtual mass point, VM, which is assumed to locate at the mid-portion between the wrist and the elbow joint centers. The RE-model was developed through analytical processes, in which the physical parameters of the human arm system were based on achieving a perfect RE-model. The RE-model for replicating the joint torques consists of the sum of linearly scaled moment per unit mass responsible for the linear and for the angular acceleration of the VM with respect to the shoulder and elbow joints, respectively. The biological reality of the RE-model was examined by assuming that the acceleration vectors of the VM resolved along a polar coordinate system might be the direct sources of information enabling central specification of the control inputs to the peripheral muscles. It was suggested that appropriate choice of the parameters of the musculoskeletal system would allow scaling control input to the muscles linearly in terms of resolved acceleration vectors. Theoretical advantages of the RE-model in motor control were considered as one way to obviate complex inverse computations toward execution