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First published online on March 24, 2005.
Copyright © 2005 by The Physiological Society
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jphysiol.2005.084772v1
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Received February 8, 2005
Revised March 21, 2005
Accepted after revision March 21, 2005

REVERSALS OF ANTICIPATORY POSTURAL ADJUSTMENTS DURING VOLUNTARY SWAY

Vijaya Krishnamoorthy1 and Mark L. Latash2*

1 University of Delaware
2 Penn State University

* To whom correspondence should be addressed. E-mail: mll11{at}psu.edu.

We describe reversals of anticipatory postural adjustments (APAs) with the phase of a voluntary cyclic whole-body sway movement. Subjects (n=9) held a standard load in extended arms and released it by a bilateral shoulder abduction motion in a self-paced manner at different phases of the sway. The load release task was also performed during quiet stance in three positions, in the middle of the sway range and close to its extreme forward and backward positions. Larger APAs were seen during the sway task as compared to quiet stance. Although the direction of postural perturbation associated with the load release was always the same, the direction of the APAs in the leg muscles reversed when the subjects were close to the extreme forward position as compared to the APAs in other phases and during quiet stance. The trunk muscles showed smaller APA modulation at the extreme positions but larger modulation when passing through the middle position, depending on the direction of sway, forward or backward. The phenomenon of APA reversals emphasizes the important role of safety in the generation of postural adjustments associated with voluntary movements.


Key words: Balance • Electromyogram • Postural control







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