Linear time delay methods and stability analyses of the human spine. Effects of neuromuscular reflex response.

Full Abstract

Linear stability methods were applied to a biomechanical model of the human musculoskeletal spine to investigate effects of reflex gain and reflex delay on stability. Equations of motion represented a dynamic 18 degrees-of-freedom rigid-body model with time-delayed reflexes. Optimal muscle activation levels were identified by minimizing metabolic power with the constraints of equilibrium and stability with zero reflex time delay. Muscle activation levels and associated muscle forces were used to find the delay margin, i.e., the maximum reflex delay for which the system was stable. Results demonstrated that stiffness due to antagonistic co-contraction necessary for stability declined with increased proportional reflex gain. Reflex delay limited the maximum acceptable proportional reflex gain, i.e., long reflex delay required smaller maximum reflex gain to avoid instability. As differential reflex gain increased, there was a small increase in acceptable reflex delay. However, differential reflex gain with values near intrinsic damping caused the delay margin to approach zero. Forward-dynamic simulations of the fully nonlinear time-delayed system verified the linear results. The linear methods accurately found the delay margin below which the nonlinear system was asymptotically stable. These methods may aid future investigations in the role of reflexes in musculoskeletal stability.

Author information

Author/s: Franklin, Timothy C (TC); Granata, Kevin P (KP); Madigan, Michael L (ML); Hendricks, Scott L (SL);

Affiliation: Engineering Science and Mechanics Department, Virginia Polytechnic Institute and State University, Blacksburg,VA 24061 USA.

Grants: R01 AR46111 (Agency:NIAMS NIH HHS)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural

Journal: IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society (IEEE Trans Neural Syst Rehabil Eng), published in United States. (Language: eng)

Reference: 2008-Aug; vol 16 (issue 4) : pp 353-9

Dates: Created 2008/08/14; Completed 2008/10/27;

PMID: 18701383, status: MEDLINE (last retrieval date: 2/18/2009, IMS Date: )

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