Stability constraints for the distributed control of motor behavior

We> have> investigated the> relation between static stability of a limb, equilibrium-point control, and the ill-posed problem of coordinating a redundant ensemble of muscles. Geometrically, equilibrium-point control is equivalent to establishing a mapping between the command signals delivered to the muscles and the equilibrium corfiguraiions ofa limb. A necessary condition for the existence ofsuch mapping is that the limb be stable across the workspace. We analyzed howthis condition may be translated intoprecisebiomechanicalconstraintsfor single-and multi-joint limbs. The satisfaction ofthese constraintsis necessary for the equilibrium-point hypothesis to be a viable control paradigm. We> show howthese same constraints are sufficient 10 insure the successful operation of a distributed algorithm based upon minimization ofpotential energy that computes the muscle-control signals corresponding to a desiredlime sequence of equilibrium points.