Characterizing Postural Stability in a Quasi-Static Sitting Position among Individuals with Sensorimotor Impairments Following Spinal Cord Injury

The objective of this study was to determine a minimum data set of postural measures to characterize seated stability in individuals with spinal cord injury (SCI) by computing 39 Center-Of-Pressure (COP) measures routinely investigated in standing posture. Two short-sitting positions on an instrumented seat with the feet resting on force plates were compared between 14 individuals with SCI and 14 healthy controls: 1) with both hands on their thighs and 2) with both upper extremities flexed at 70 o and abducted at 45 o . The correlations between all COP measures for the resultant, anteroposterior and mediolateral components were also computed. Differences in seated stability were observed between individuals with SCI and healthy controls, irrespective of the tasks. More precisely, the bilateral hand support was confirmed to be an effective strategy to compensate for anterior instability in individuals with SCI. As anticipated, time domain distance and frequency domain measures revealed complementary information. Distance and area COP measures were highly correlated with each other (i.e., redundant information) but were not correlated with frequency and hybrid measures. For both groups (between-task comparisons), the most discriminative uncorrelated measures were related to frequency parameters (i.e., independent information). Overall, our analyses revealed that a minimal data set of postural measures should include mean distance, mean velocity, centroidal frequency, median power frequency and frequency dispersion. These measures should be reported for all directional components whenever applicable, as both anteroposterior and mediolateral activities independently contribute to the resultant COP outcome measures.