Effect of predictability of the magnitude of a perturbation on anticipatory and compensatory postural adjustments

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RESEARCH ARTICLE

Effect of predictability of the magnitude of a perturbation on anticipatory and compensatory postural adjustments Tippawan Kaewmanee1 · Huaqing Liang2 · Alexander S. Aruin2  Received: 27 February 2020 / Accepted: 13 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Balance maintenance in response to a perturbation could be affected by the predictability of the magnitude of the body disturbance. We investigated anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to perturbations of predictable and unpredictable magnitudes. Twenty young adults received series of perturbations of small or large magnitudes the order of which was varied. Electromyographic activity of six leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded. The muscle onset time, integrals of muscle activity, and COP displacements in the anterior–posterior direction were analyzed during the APA and CPA phases. The results indicated that when the participants were exposed to the repeated perturbation magnitude, it became predictable and they generated APAs more precisely according to the magnitudes of the perturbation. Moreover, when the magnitude of perturbation changed unpredictably, the participants overestimated or underestimated the magnitudes of the perturbation, as they generated APAs based on their prior experience of dealing with the perturbation. The optimal adjustment of APAs occurred after five trials of repeated perturbations. The findings imply that the process of APAs and CPAs generation depends on the accuracy of the predictability of perturbation magnitudes. Keywords  Predictability · Perturbation · Magnitude · Anticipatory postural adjustments · Compensatory postural adjustments

Introduction To maintain a vertical posture, the central nervous system (CNS) employs anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs). APAs function as a feedforward control in regulating the position of the center of mass of the body by activating trunk and leg muscles prior to the predicted upcoming postural perturbation (Massion 1992; Toussaint et al. 1997). CPAs are initiated by the sensory feedback signals and are used to Communicated by Winston D. Byblow. * Alexander S. Aruin [email protected] 1



PhD Program in Rehabilitation Sciences, College of Applied Health Sciences, University of Illinois at Chicago, Chicago, USA



Department of Physical Therapy (MC 898), University of Illinois at Chicago, 1919 W. Taylor St, Chicago, IL 60612, USA

2

restore the position of the center of mass of the body after perturbation has already occurred (Alexandrov et al. 2005; Le Bozec et al. 2008). Previous studies have reported the existence of a relationship between APAs and CPAs: when sufficient APAs were generated prior to the external body perturbation, smaller CPAs were seen after the perturbation which indicated better overall balance control (Santos et al. 2010a, b). A number of factors can influence the generation of APA