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Two stages and three components of the postural preparation to action

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Title: Two stages and three components of the postural preparation to action
Author(s): Krishnan, Vennila; Aruin, Alexander S.; Latash, Mark L.
Subject(s): Synergy anticipatory postural adjustment posture preparation to action
Abstract: Previous studies of postural preparation to action/perturbation have primarily focused on anticipatory postural adjustments (APAs), the changes in muscle activation levels resulting in the production of net forces and moments of force. We hypothesized that postural preparation to action consists of two stages: (1) Early postural adjustments (EPAs), seen a few hundred ms prior to an expected external perturbation; and (2) APAs seen about 100 ms prior to the perturbation. We also hypothesized that each stage consists of three components, anticipatory synergy adjustments seen as changes in co-variation of the magnitudes of commands to muscle groups (M-modes), changes in averaged across trials levels of muscle activation, and mechanical effects such as shifts of the center of pressure. Nine healthy participants were subjected to external perturbations created by a swinging pendulum while standing in a semi-squatting posture. Electrical activity of twelve trunk and leg muscles and displacements of the center of pressure were recorded and analyzed. Principal component analysis was used to identify four M-modes within the space of muscle activations using indices of integrated muscle activation. This analysis was performed twice, over two phases, 400-700 ms prior to the perturbation and over 200 ms just prior to the perturbation .Similar robust results were obtained using the data from both phases. An index of a multi-M-mode synergy stabilizing the center of pressure displacement was computed using the framework of the uncontrolled manifold hypothesis. The results showed high synergy indices during quiet stance. Each of the two stages started with a drop in the synergy index followed by a change in the averaged across trials activation levels in postural muscles. There was a very long electromechanical delay during the early postural adjustments and a much shorter delay during the APAs. Overall, the results support our main hypothesis on the two stages and three components of the postural preparation to action/perturbation. This is the first study to document anticipatory synergy adjustments in whole-body tasks. We interpret the results within the referent configuration hypothesis (an extension of the equilibrium-point hypothesis): The early postural adjustment is based primarily on changes in the co-activation command while the APAs involve changes in the reciprocal command. The results fit an earlier hypothesis that whole-body movements are controlled by a neuromotor hierarchy where each level involves a few-to-many mapping organized to stabilize its overall output.
Issue Date: 2011-07
Publisher: Springer Verlag
Citation Info: Krishnan, V., Aruin, A. S., & Latash, M. L. 2011. Two stages and three components of the postural preparation to action. Experimental Brain Research. 2011 Jul;212(1):47-63. DOI: 10.1007/s00221-011-2694-z
Type: Article
Description: This is a copy of an article published in the journal Experimental Brain Research © 2011 Springer Verlag. The original publication is available at www.springerlink.com 10.1007/s00221-011-2694-z
URI: http://hdl.handle.net/10027/8344
ISSN: 0014-4819
Date Available in INDIGO: 2012-05-27
 

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