Quantification of trunk segmental coordination and head stability in laterally unstable sitting identifies aging and cerebellar ataxia.

BACKGROUND: We quantified trunk segmental coordination and head stability in unstable sitting and investigated whether it can discriminate postural control, age-related differences and presence of coordination disorder.

METHODS: Subjects were a healthy younger group (n = 7), a healthy elderly group (n = 7), and a cerebellar ataxia group (n = 8). The motion sensors and surface electrodes were located on the trunk and/or head segments to measure angle displacements, acceleration and electromyograms in unstable sitting during a lateral tilt task. Trunk lateral angle cross-correlation and electromyogram cross-correlation for the trunk segmental coordination, head root mean square (RMS) for the head stability, clinical performance scales, and gait parameters (velocity, coefficient of variation, and RMS ratio) were analyzed.

FINDINGS: Trunk lateral angle cross-correlation showed a significantly negative correlation in the healthy younger group compared with the two other groups (p < 0.01). Head RMS showed a significantly larger value in the cerebellar ataxia group compared with the two other groups (p < 0.01). Trunk lateral angle cross-correlation had moderate correlation with the clinical performance scale of ataxia and gait parameters; however, it was not correlated with head RMS. Classification using trunk lateral angle cross-correlation and head RMS was validated by discriminant analysis and hierarchical cluster analysis.

INTERPRETATION: We found that trunk lateral angle cross-correlation reflected age-related differences and head RMS characterized the pathology of cerebellar ataxia. Trunk segmental coordination and head stability, as two aspects of sitting postural control, can be used to discriminate the degree of aging and cerebellar ataxia.