Effects of reflex delays on postural control during unstable seated balance |
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| Authors: | N. Peter Reeves Jacek Cholewicki Kumpati S. Narendra |
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| Affiliation: | 1. Department of Surgical Specialties, College of Osteopathic Medicine, Michigan State University, Ingham Regional Orthopedic Hospital, 2727 S. Pennsylvania Avenue Room 235, Lansing, MI 48910, USA;2. Department of Electrical Engineering, Yale University, USA;1. Arts et Metiers ParisTech, LBM/Institut de Biomecanique Humaine Georges Charpak, 151 bd de l''Hopital, 75013 Paris, France;2. Service de Chirurgie Orthopédique et Réparatrice de l’Enfant, Hôpital Armand Trousseau, 26 avenue du Dr Netter, F-75012 Paris, France;3. Département Hospitalo-Universitaire “Maladies Musculo-Squelettiques et Innovations Thérapeutiques” DHU-MAMUTH, Hôpital Armand Trousseau, 26 avenue du Dr Netter, F-75012 Paris, France;1. MSU Center for Orthopedic Research, Michigan State University, USA;2. Department of Osteopathic Surgical Specialties, Michigan State University, USA;3. Department of Mechanical Engineering, Michigan State University, USA;4. Department of Electrical and Computer Engineering, Michigan State University, USA;1. Faculty of Health Sciences, Hokkaido University, Sapporo, Japan;2. Department of Rehabilitation, Hokkaido University Hospital, Sapporo, Japan;3. Rehabilitation Center, NTT East Japan Sapporo Hospital, Sapporo, Japan;4. Faculty of Health Science, Hokkaido Chitose College of Rehabilitation, Chitose, Japan;5. Department of Rehabilitation, Fukushima Medical University Aizu Medical Center, Aizuwakamatsu, Japan;1. Human-Centric Design Research Lab, Department of Mechanical Engineering, Texas Tech University, Lubbock, TX 79409, USA;2. Department of Mechanical and Manufacturing Engineering, Miami University, Oxford, OH 45056, USA;1. Division of Applied Mechanics, Department of Mechanical Engineering, École Polytechnique, Montréal, Québec, Canada;2. Institut de recherche Robert Sauvé en santé et en sécurité du travail, Montréal, Québec, Canada |
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| Abstract: | Patients with low-back pain (LBP) exhibit longer trunk muscle reflex latencies and poorer postural control than healthy individuals. We hypothesized that balance during a simulated postural control task would become impaired when the delays exhibited by LBP patients were incorporated into neuromuscular control. The task chosen for this investigation was seated balancing, which emphasizes trunk muscles’ contribution in postural control. This task was modeled in Simulink? as a fourth order linearized dynamic system with feedback delays. Optimization (minimizing error between experimental and model data) of state variables was used to determine neuromuscular control parameters. Experimental data were obtained from 7 subjects during 5 perturbation trials while balancing on the seat with eyes closed. Model accuracy, reflecting the ability of the model to capture the dynamics of seated balance, was correlated with seated balance performance (r=0.91, p<0.001). To minimize the risk of erroneous findings from inaccurate modeling, only the best five balancers’ data were used for hypothesis testing. In these five subjects, feedback delays in modeled neuromuscular control were increased to determine their effect on task stability, trunk displacement and trunk moment. Simulations showed that longer delays found in LBP, in general, did not produce unstable balancing, but did result in increased trunk displacement (p<0.001) and trunk moment (p=0.001). This impairment in neuromuscular control in chronic LBP patients could possibly exacerbate their condition by increasing tissue strain (more spinal displacement) and stress (more spinal loading). |
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