Increased obstacle clearance in people with ARCA-1 results in part from voluntary coordination changes between the thigh and shank segments.

Obstacle clearance can be a hazardous locomotor task if not coordinated with the utmost accuracy. The current study explored changes in leading limb segment coordination during obstacle clearance in a population with cerebellar ataxia using the planar law of intersegmental coordination. Eight participants with ARCA-1, caused by mutations in the SYNE-1 gene, and eight healthy adults stepped over obstacles. Healthy adults walked at natural speeds, as well as a velocity similar to the participants with cerebellar ataxia, resulting in three groups [healthy (H), matched velocity (MV) and cerebellar ataxia (CA)]. Elevation angles of the foot, shank and thigh in the sagittal plane were calculated. A principal component analysis was applied to limb segment trajectories, and a Fourier harmonic series was further used to determine temporal phase differences between adjacent segments. Although obstacle clearance was greater in the CA group, the planar nature of the 3D covariance plot of segment elevation angles, the covariance loop width and orientation did not differ between the CA, H and MV groups, suggesting that the planar patterns between elevation angles may not be heavily influenced by the cerebellum. Further analysis led to the observation of a nonlinear relationship between covariance loop width and thigh-shank fundamental harmonic phase difference, and a decrease in covariance loop width was observed when the fundamental harmonic phase difference between the thigh and shank segments is >90°. This study supports previous work that a greater safety margin is used in people with cerebellar ataxia when stepping over obstacles, but reveals a mechanism of segmental coordination to facilitate this increase in toe clearance. Further work is required to determine whether ataxia severity has an effect on the observed coordination variables.