Comparing joint kinematics and center of mass acceleration as feedback for control of standing balance by functional neuromuscular stimulation

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English
11 pages
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The purpose of this study was to determine the comparative effectiveness of feedback control systems for maintaining standing balance based on joint kinematics or total body center of mass (COM) acceleration, and assess their clinical practicality for standing neuroprostheses after spinal cord injury (SCI). Methods In simulation, controller performance was measured according to the upper extremity effort required to stabilize a three-dimensional model of bipedal standing against a variety of postural disturbances. Three cases were investigated: proportional-derivative control based on joint kinematics alone, COM acceleration feedback alone, and combined joint kinematics and COM acceleration feedback. Additionally, pilot data was collected during external perturbations of an individual with SCI standing with functional neuromuscular stimulation (FNS), and the resulting joint kinematics and COM acceleration data was analyzed. Results Compared to the baseline case of maximal constant muscle excitations, the three control systems reduced the mean upper extremity loading by 51%, 43% and 56%, respectively against external force-pulse perturbations. Controller robustness was defined as the degradation in performance with increasing levels of input errors expected with clinical deployment of sensor-based feedback. At error levels typical for body-mounted inertial sensors, performance degradation due to sensor noise and placement were negligible. However, at typical tracking error levels, performance could degrade as much as 86% for joint kinematics feedback and 35% for COM acceleration feedback. Pilot data indicated that COM acceleration could be estimated with a few well-placed sensors and efficiently captures information related to movement synergies observed during perturbed bipedal standing following SCI. Conclusions Overall, COM acceleration feedback may be a more feasible solution for control of standing with FNS given its superior robustness and small number of inputs required.

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Publié le 01 janvier 2012
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Langue English
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Natarajet al. Journal of NeuroEngineering and Rehabilitation2012,9:25 http://www.jneuroengrehab.com/content/9/1/25
R E S E A R C H
JOURNAL OF NEUROENGINEERING J N E R AND REHABILITATION
Open Access
Comparing joint kinematics and center of mass acceleration as feedback for control of standing balance by functional neuromuscular stimulation 1,2* 1,21,2,3Raviraj Nataraj , Musa L Audu and Ronald J Triolo
Abstract Background:The purpose of this study was to determine the comparative effectiveness of feedback control systems for maintaining standing balance based on joint kinematics or total body center of mass (COM) acceleration, and assess their clinical practicality for standing neuroprostheses after spinal cord injury (SCI). Methods:In simulation, controller performance was measured according to the upper extremity effort required to stabilize a threedimensional model of bipedal standing against a variety of postural disturbances. Three cases were investigated: proportionalderivative control based on joint kinematics alone, COM acceleration feedback alone, and combined joint kinematics and COM acceleration feedback. Additionally, pilot data was collected during external perturbations of an individual with SCI standing with functional neuromuscular stimulation (FNS), and the resulting joint kinematics and COM acceleration data was analyzed. Results:Compared to the baseline case of maximal constant muscle excitations, the three control systems reduced the mean upper extremity loading by 51%, 43% and 56%, respectively against external forcepulse perturbations. Controller robustness was defined as the degradation in performance with increasing levels of input errors expected with clinical deployment of sensorbased feedback. At error levels typical for bodymounted inertial sensors, performance degradation due to sensor noise and placement were negligible. However, at typical tracking error levels, performance could degrade as much as 86% for joint kinematics feedback and 35% for COM acceleration feedback. Pilot data indicated that COM acceleration could be estimated with a few wellplaced sensors and efficiently captures information related to movement synergies observed during perturbed bipedal standing following SCI. Conclusions:Overall, COM acceleration feedback may be a more feasible solution for control of standing with FNS given its superior robustness and small number of inputs required. Keywords:Biomechanics, Standing balance, Biomedical engineering technology, Rehabilitation
Background The goal of this study was to assess the potential perform ance of control systems employing feedback of total body center of mass (COM) acceleration and proportional derivative joint feedback from the ankles, knees, hips, and trunk for comprehensive control of standing after spinal
* Correspondence: raviraj.nataraj@gmail.com Equal contributors 1 Biomedical Engineering Department, Case Western Reserve University, Cleveland, OH, USA 2 Motion Study Laboratory, Louis Stokes Veterans Affairs Medical Center, Cleveland, OH, USA Full list of author information is available at the end of the article
cord injury (SCI). Neuroprostheses employing functional neuromuscular stimulation (FNS) have been proven clinic ally effective for restoring basic standing function follow ing SCI [1] using preprogrammed patterns of stimulation to produce the sittostand maneuver and continuous stimulation at constant levels to maintain upright posture. Under constant stimulation, balance is maintained through upper extremity (UE) loads applied to the envir onment (e.g., walker, countertop). Sustained UE loading compromises the utility of standing with FNS by limiting the functional use of the hands and arms and reducing standing time due to rapid upper body fatigue. Feedback
© 2012 Nataraj et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.