Because the motor control system is able to perform an almost limitless array of movements, it is usually blessed in a very broad sense with a surplus number of degrees of freedom when it is required to perform any single movement. Despite this fact, when evaluated quantitatively, human (and primate) voluntary movements display a considerable degree of kinematic consistency both within and across subjects. Over the last six years, we have discovered that there is often an equal or greater degree of consistency when movement is evaluated at the level of joint torques. We have postulated that kinematic consistency is a consequence of internal rules for the generation of joint torque patterns. When external constraints on performance are modest (as they are for many of our common movements), the CNS imposes an internal constraint. That constraint is to apply similar torque patterns at multiple joints so that, when plotted in a joint torque space, the torque trajectory lies close to a straight line, a """"""""linear synergy."""""""" The necessary corollary of this is that if there are external constraints that are incompatible with linear synergy, the CNS must learn to use a more complex, nonlinear strategy. The research described here is intended clarify the circumstances under which linear synergy is present and when it is not. 1) We will examine if movements to targets that are made around intermediate, """"""""via-point"""""""" targets, can be decomposed into two serial movements, each of which obeys linear synergy although the movement as a whole does not. 2) We will examine how the application of an external load alters linear synergy for movements of different directions. 3) We will explore linear synergy during gait to see if the imposition of swing-phase constraints reduces linear synergy. 4) We will explore the gait of patients with stroke to test the hypothesis that pathological movement deficits reflect either the inability to control the independent scaling of torques at different joints or the inability to break away from linear synergy when the task requires. ? ?
