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This Article Full Text Full Text (PDF) All Versions of this Article: 565/2/675    most recent jphysiol.2005.084772v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Krishnamoorthy, V. Articles by Latash, M. L. Search for Related Content PubMed PubMed Citation Articles by Krishnamoorthy, V. Articles by Latash, M. L.

¹ Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
² Department of Physical Therapy, University of Delaware, Newark, DE 19716, USA

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. Based on these findings, APAs could be defined as changes in the activity of postural muscles associated with a predictable perturbation that act to provide maximal safety of the postural task component.

(Received 8 February 2005; accepted after revision 21 March 2005; first published online 24 March 2005)
Corresponding author M. L. Latash: Rec. Hall - 267L, Department of Kinesiology, Penn State University, University Park, PA 16802, USA. Email: mll11{at}psu.edu