Loss of differential muscle control leads to weakness and discoordination in individuals with acute hemiparetic stroke

Motor impairment in the affected lower extremity of acute hemiparetic stroke patients was evaluated by quantifying the control strategies these patients utilize to generate maximum isometric torques at the hip and knee joints. For each direction tested, which included hip flexion-extension, abduction-adduction, internal-external rotation, and knee flexion-extension, torques generated simultaneously at the knee and hip were quantified, along with associated muscle activation patterns in eight lower limb muscles. In each direction tested, stroke subjects generated significantly less torque than age-matched control subjects. Furthermore, the control strategies stroke subjects utilized during these maximum exertions, in terms of muscles activation patterns and synergistic torque coupling, were commonly different than the control subjects. Interestingly, some stroke subjects were able to generate torques in the range of the control group along certain directions while attempting to exert maximum torques along a different, non-preferred direction. Our findings suggest that the inability to differentially control muscle groups appropriate for specific tasks leads to weakness and the loss of coordination in the lower extremity of hemiparetic stroke subjects. We propose that goal-directed neurorehabilitation forcing selective muscle control may re-establish descending control over lower limb muscles.