Strength and coordination in the paretic leg of individuals following acute stroke

Abstract

The goal of this study was to determine whether acute stroke survivors demonstrate abnormal synergy patterns in their affected lower extremity. During maximum isometric contractions with subjects in a standing position, joint torques generated simultaneously at the knee and hip were measured, along with associated muscle activation patterns in eight lower limb muscles. Ten acute stroke survivors and nine age-match controls participated in the study. For all joints tested, stroke subjects demonstrated significantly less maximum isometric torque than age-matched control subjects. However, the synergistic torques generated in directions different than the direction that was being maximized were not significantly different between the two groups. According to electromyography (EMG) data, it was found that stroke subjects activated antagonistic muscle groups significantly higher than the control group subjects, suggesting that deficits in joint torque may be at least partially attributable to co-contraction of antagonistic muscles. Our findings suggest that a primary contributor to lower limb motor impairment in acute hemiparetic stroke is poor volitional torque generating capacity, which is at least partially attributable to co-contraction of antagonistic muscles. Furthermore, while we did not observe abnormal torque synergy patterns commonly found in the upper limbs, muscle activation patterns differed between groups for many of the directions tested indicating changes in the motor control strategies of acute stroke survivors.