Effects of altered center of mass trajectory on stiff knee gait after stroke

Excessive center of mass (CoM) shift toward the paretic side may increase muscle activity required for weight support, potentially causing abnormal activation that impairs the subsequent swing phase. To clarify the unique characteristics of the CoM trajectory and the associated abnormal lower limb muscle activity in poststroke patients with stiff knee gait (SKG).

Kinematic parameters-including CoM trajectory and joint motion derived from inertial sensors-and lower-limb muscle synergy data from electromyography were analyzed in 20 poststroke patients with SKG and 16 without SKG walking at a comfortable speed. Analysis of covariance was performed to compare kinematic parameters between groups, using walking speed as a covariate. Subsequently, correlations between CoM parameters and knee joint kinematics or synergy activity were examined within each group.

Analysis of covariance demonstrated that the SKG group exhibited a prolonged mediolateral CoM transfer period from the paretic to the nonparetic side compared with the non-SKG group. Correlation analysis revealed that, within the SKG group, a CoM positioned closer to the paretic foot and a longer mediolateral transfer period were associated with greater reductions in knee flexion, as well as increased abnormal activity in the early swing and early stance synergy modules.

The observed associations suggest that swing-phase muscles may assume a compensatory weight-bearing role in response to altered mediolateral CoM control. Modifying mediolateral CoM control may influence SKG; however, further interventional studies are warranted.