Abstract
In people with severe neuromotor deficits of trunk and lower extremities, regaining balance in standing is often performed in rehabilitation with manual assistance, rigid body supports or by the use of handrails. To investigate and further expand postural control training in standing, we developed a Robotic Upright Stand Trainer (RobUST). In this study, we used RobUST to deliver trunk perturbations while simultaneously providing postural assistive forces on the pelvis in 10 able-bodied adults. Posture control responses with 'pelvic support' was then compared to 'no support' and 'hand supported' standing, with and without assistance from RobUST. We characterize postural imbalance with kinematic displacements and center of pressure (COP) outcomes, such as amplitude and root mean square of the excursions of COP. Surface electromyography (sEMG) was also applied to investigate muscle control. We additionally investigated ground reaction and handrail forces during standing to analyze how postural strategies and muscle mechanisms with 'pelvic support' via RobUST would differ from standing with 'no support' and with the 'handrail support'. Our results show that during perturbations, pelvic assistive support decreased kinematic and COP excursions compared to standing with no support. The pelvic assistance from RobUST showed similar level of COP changes as the use of handrail support but without reducing muscle activity or ground reaction forces. As expected, the maximum level of postural stability was observed when participants used the handrail and received pelvic assistive forces. In conclusion, RobUST demonstrates potential as a training device since it enhances postural balance without significantly removing muscular control mechanisms that are of interest in re-training postural control strategies in standing.
Highlights
P OSTURAL responses are task and environment dependent, and require different neuromuscular control strategies appropriate to the task [1], [2]
We tested the dual action of Robotic Upright Stand Trainer (RobUST) to generate postural imbalance, via controlled perturbative forces interestingly, participants experienced less body displacements with pelvic assistive force support compared to postural support offered by a handrail 3) with pelvic support from RobUST, EMG activity of postural muscles resembled the muscles active during standing with no support 4) the combination of assistive force field and handrail support resulted in the greatest level of postural stability at the expense of substantial decrease in weight bearing forces between the feet and the ground
We found that the combination of hand and pelvic support via RobUST significantly reduced the handrail force magnitude exerted by participants during anterior perturbations and during the recovery stage from posterior perturbations, Fig. 8
Summary
P OSTURAL responses are task and environment dependent, and require different neuromuscular control strategies appropriate to the task [1], [2]. Unexpected perturbations disrupt the person’s equilibrium and elicit muscle responses to restore balance in standing position. These are called in-place postural strategies [4]. When muscle responses cannot overcome the postural imbalance, a person needs to perform compensatory actions such as taking a step or reaching for an external support to avoid falling. These are termed as change-in-support postural strategies [3], [5]. The goal of postural rehabilitation in neuromotor disorders is to practice and relearn in-place and change-in-support postural strategies to adapt postural control to diverse perturbations present in everyday surroundings
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