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Load-relaxation properties of the human trunk in response to prolonged flexion: measuring and modeling the effect of flexion angle.

Authors
Toosizadeh-N; Nussbaum-MA; Bazrgari-B; Madigan-ML
Source
PLoS One 2012 Nov; 7(11):e48625
NIOSHTIC No.
20042534
Abstract
Experimental studies suggest that prolonged trunk flexion reduces passive support of the spine. To understand alterations of the synergy between active and passive tissues following such loadings, several studies have assessed the time-dependent behavior of passive tissues including those within spinal motion segments and muscles. Yet, there remain limitations regarding load-relaxation of the lumbar spine in response to flexion exposures and the influence of different flexion angles. Ten healthy participants were exposed for 16 min to each of five magnitudes of lumbar flexion specified relative to individual flexion-relaxation angles (i.e., 30, 40, 60, 80, and 100%), during which lumbar flexion angle and trunk moment were recorded. Outcome measures were initial trunk moment, moment drop, parameters of four viscoelastic models (i.e., Standard Linear Solid model, the Prony Series, Schapery's Theory, and the Modified Superposition Method), and changes in neutral zone and viscoelastic state following exposure. There were significant effects of flexion angle on initial moment, moment drop, changes in normalized neutral zone, and some parameters of the Standard Linear Solid model. Initial moment, moment drop, and changes in normalized neutral zone increased exponentially with flexion angle. Kelvin-solid models produced better predictions of temporal behaviors. Observed responses to trunk flexion suggest nonlinearity in viscoelastic properties, and which likely reflected viscoelastic behaviors of spinal (lumbar) motion segments. Flexion-induced changes in viscous properties and neutral zone imply an increase in internal loads and perhaps increased risk of low back disorders. Kelvin-solid models, especially the Prony Series model appeared to be more effective at modeling load-relaxation of the trunk.
Keywords
Biomechanical-modeling; Biomechanics; Body-mechanics; Body-regions; Physiological-function; Physiological-testing; Models; Motion-studies; Humans; Men; Women; Weight-factors; Tissue-distribution; Muscle-physiology; Muscle-tissue; Spinal-cord; Viscosity; Analytical-models; Analytical-processes; Physiological-stress; Elastic-properties
Contact
Maury A. Nussbaum, Department of Industrial and System Engineering, Virginia Tech, Blacksburg, VA, USA
CODEN
POLNCL
Publication Date
20121105
Document Type
Journal Article
Email Address
nussbaum@vt.edu
Funding Type
Grant
Fiscal Year
2013
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-008504
Issue of Publication
11
ISSN
1932-6203
Source Name
Public Library of Science One
State
VA; KY
Performing Organization
Virginia Polytechnic Institute and State University
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