Abstract
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 70o and abducted at 45o. 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.
Highlights
Individuals with a Spinal Cord Injury (SCI) often experience various degrees of motor or sensory impairments that can affect their trunk as well as their Upper Extremities (U/Es) and lower extremities depending on the neurological level and the completeness of the injury to the spinal cord
The rapid sublesional bone mineral density loss [2], in addition to muscle hypertrophy that frequently develops at the U/Es, raises the height of the center of mass (COM)
All center of pressure (COP) measures calculated during supported and unsupported sitting obtained for individuals with SCI and able-bodied individuals are summarized in table 3, as well as between- and within-group comparisons
Summary
Individuals with a Spinal Cord Injury (SCI) often experience various degrees of motor or sensory impairments that can affect their trunk as well as their Upper Extremities (U/Es) and lower extremities depending on the neurological level and the completeness of the injury to the spinal cord (i.e., impaired sensorimotor pathways originating in the spinal cord). The rapid sublesional bone mineral density loss [2], in addition to muscle hypertrophy that frequently develops at the U/Es (except in individuals with high SCI who generally develop hypotrophy at the U/Es), raises the height of the center of mass (COM) (i.e., the relative body mass in individuals with SCI was more in the upper body compared to able-bodied individuals) This may further jeopardize the ability to secure quasi-static sitting postural stability following SCI which may, in turn, affect the ability to perform certain functional activities in daily life, especially activities that solicit the U/ Es [3]. Prieto et al [15] proposed 39 COP-related outcome measures linked to time and frequency domains to investigate age-related change in standing postural stability. Rocchi et al [16] investigated the amount of redundancy
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