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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.

Background Sitting pivot transfer (SPT) is one of the most important, but at the same time strenuous at the upper extremity, functional task for spinal cord injured individuals. In order to better teach this task to those individuals and to improve performance, a better biomechanical understanding during the different SPT phases is a prerequisite. However, no consensus has yet been reached on how to depict the different phases of the SPT. The definition of the phases of the SPT, along with the events characterizing these phases, will facilitate the interpretation of biomechanical outcome measures related to the performance of SPTs as well as strengthen the evidence generated across studies. Methods Thirty-five individuals with a spinal cord injury performed two SPTs between seats of similar height using their usual SPT technique. Kinematics and kinetics were recorded using an instrumented transfer assessment system. Based on kinetic and kinematic measurements, a relative threshold-based algorithm was developed to identify four distinct phases: pre-lift, upper arm loading, lift-pivot and post-lift phases. To determine the stability of the algorithm between the two SPTs, Student t-tests for dependent samples were performed on the absolute duration of each phase. Results The mean total duration of the SPT was 2.00 ± 0.49 s. The mean duration of the pre-lift, upper arm loading, lift-pivot and post-lift phases were 0.74 ± 0.29 s, 0.28 ± 0.13 s, 0.72 ± 0.24 s, 0.27 ± 0.14 s whereas their relative contributions represented approximately 35%, 15%, 35% and 15% of the overall SPT cycle, respectively. No significant differences were found between the trials (p = 0.480-0.891). Conclusion The relative threshold-based algorithm used to automatically detect the four distinct phases of the SPT, is rapid, accurate and repeatable. A quantitative and thorough description of the precise phases of the SPT is prerequisite to better interpret biomechanical findings and measure task performance. The algorithm could also become clinically useful to refine the assessment and training of SPTs.