Inclination angles of the ankle and head relative to the centre of mass identify gait deviations post-stroke

Background: Whole-body movement adjustments during gait are common post-stroke, but comprehensive ways of quantifying and evaluating gait from a whole-body perspective are lacking. Research question: Can novel kinematic variables related to Center of Mass (CoM) position discriminate side asymmetries as well as coordination between the upper and lower body during gait within persons post-stroke and compared to non-disabled controls? Methods: Thirty-one persons post-stroke and 41 age-matched non-disabled controls walking at their self-selected speed were recorded by 3D motion capture. The Ankle-CoM Inclination Angle (A-CoMIA) and the Head-CoM Inclination Angle (H-CoMIA) defined the angle between the CoM and the ankle and the head, respectively, in the frontal plane. These angles and their angular velocities were compared between groups, and with regard to motor impairment severity during all phases of the gait cycle (GC) using a functional interval-wise testing analysis suitable for curve data. Upper and lower body coordination was assessed using crosscorrelation. Results: The A-CoMIA was symmetrical between body sides in persons post-stroke but larger compared to controls. The angular velocity of A-CoMIA also differed when compared to controls. The H-CoMIA was consistently asymmetrical in persons post-stroke and larger than in controls throughout the stance phase. There were only minor group differences in the angular velocity of H-CoMIA, with some side asymmetry in persons post-stroke. The A-CoMIA of the non-affected side, and the HCoMIA, discriminated between persons with more severe impairments compared to those with milder impairments post-stroke. The variables showed strong cross correlations in both groups. Significance: The A-CoMIA and Head-CoMIA discriminated post-stroke gait from non-disabled, as well as motor impairment severity. These variables with the advantageous curve analysis during the entire GC add valuable whole-body information to existing parameters of post-stroke gait analysis through assessment of symmetry and upper and lower body coordination.