Constraints imposed by the lower extremity extensor synergy in chronic hemiparetic stroke: Preliminary findings

In the present manuscript we implemented the MultiLEIT, a lower extremity isometric torque measurement device to quantify spontaneous joint torque coupling during maximal torque generation in the paretic leg of in chronic hemiparetic stroke. We quantified extension/adduction coupling (coincident with the clinical extension synergy) during the generation of hip extension and ankle plantarflexion maximum voluntary torques. Subjects were then instructed to generate torques outside the synergy by combining hip extension+ hip abduction or ankle plantarflexion + hip abduction. During the hip dual task, the paretic hip torques were significantly different from those measured in the non-paretic and control leg (F = 22.9719, p = 0) and resulted in the inability to generate torques outside the extensor synergy patters. During the dual ankle/ hip task, the paretic extremity generated significantly smaller hip abduction torques compared to controls and to the non-paretic extremity (F = 15.861, p = 0). During this task the paretic extremity was capable of neutralizing the spontaneous adduction torque and generate a net albeit small abduction torque. Results may indicate an increased descending drive from brain stem pathways, particularly during hip extension, responsible for constraints in generating hip abduction torques after stroke.