Manual wheelchair users gradually face fewer postural stability and control challenges with increasing rolling resistance while maintaining a rear-wheel wheelie.

Teaching manual wheelchair users to perform wheelies using various rolling resistances is expected to facilitate learning of this advanced wheelchair skill. However, limited scientific evidence is available to support this approach. This study aimed to measure and compare postural stability and control requirements when maintaining a stationary wheelie on different rolling resistances. Eighteen manual wheelchair users with a spinal cord injury performed in a random order and maintained four 30-second wheelies on four rolling resistances: natural hard floor (NAT), 5-cm thick soft foam (LOW), 5-cm thick memory foam (MOD), and rear wheels blocked by wooden blocks (HIGH). All wheelies were performed over a large instrumented force plate to continuously record the center of pressure (CoP). To quantify postural stability, resultant and directional time- and frequency-domain CoP measures were computed and compared across all four rolling resistances. All resultant time-domain measures confirmed increased postural stability from NAT to LOW and from MOD to HIGH rolling resistances. Most time-domain measures confirmed a shift in postural control from an anticipatory to a predominantly compensatory strategy, accompanied by increased reliance on proprioceptive feedback, especially from NAT to LOW and from MOD to HIGH rolling resistances. Postural stability gradually increased with various rolling resistances while maintaining a stationary wheelie, whereas the postural control strategy shifted from an anticipatory to a reactive strategy. Blocking the rear wheels is recommended when first teaching this advanced wheelchair skill. Rapid progression on foam and natural surfaces is advocated to refine learning and enhance proper postural control strategies.

Postural regulatory strategies during quiet sitting are affected in individuals with thoracic spinal cord injury.

Thoracic spinal cord injury (SCI) can have significant negative consequences, which can affect the ability to maintain unsupported sitting. The objectives of this study were to compare postural control of individuals with high- and low-thoracic SCI to able-bodied people and evaluate the effects of upper-limb support on postural control during quiet sitting. Twenty-five individuals were recruited into: (a) high-thoracic SCI; (b) low-thoracic SCI; and (c) able-body subgroups. Participants were seated and asked to maintain a steady balance in the following postures: (1) both hands resting on thighs; (2) both arms crossed over the chest; and (3) both arms extended. Center of pressure (COP) fluctuations were evaluated to compare postural performance between groups and different postures. Results showed that individuals with high- and low-thoracic SCI swayed more compared to the able-bodied group regardless of upper-limb support. No differences between the two SCI groups were observed, but the neurological level of injury was correlated to postural performance implying that those with higher injuries swayed more and faster. Unsupported sitting was more unstable in comparison to supported sitting posture, especially in the anterior-posterior direction. The velocity of postural sway was not different between groups, but the results suggest that postural regulation had unique effect during different postures in different groups. These results imply reduced postural stability after thoracic SCI. Overall, the way individuals with high-thoracic SCI achieved stability was different from that of individuals with low-thoracic SCI, suggesting different postural regulation strategies.

Development of an automated method to detect sitting pivot transfer phases using biomechanical variables: toward a standardized method.

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.