Compensatory but not anticipatory adjustments are altered in older adults during lateral postural perturbations Renato Claudino a , Eloá C.C. dos Santos b , Marcio J. Santos a,b,⇑ a Human Movement Sciences Graduation Program, Health Sciences and Sports Center, Santa Catarina State University, Brazil b Physical Therapy Department, Health Sciences and Sports Center, Santa Catarina State University, Brazil article info Article history: Accepted 16 February 2013 Available online 16 April 2013 Keywords: Postural control Standing External perturbations Predictable Unpredictable highlights  Anticipatory and compensatory adjustments represent the Central Nervous System’s (CNSs) ability to respond to postural disturbances, preventing loss of equilibrium and falls.  Lateral instability is a strong predictor of falls in older individuals; however, data on the modulation of these adjustments, and their relationship, in muscles that provide lateral postural stability is scarce.  Older adults used higher compensatory activity and similar anticipatory adjustments during lateral perturbations when compared to young individuals. Nevertheless, they showed greater postural instability after the postural disturbances. abstract Objective: This study investigated anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) and their relationship in older adults during lateral postural perturbations. Methods: Unpredictable and predictable postural disturbances were induced by a swinging pendulum that impacted at the shoulder level of two groups of older adults, non-fallers (20) and fallers (20), and in a group of young control subjects (20). The electromyographic (EMG) activity of the postural muscles and the center of pressure (COP) displacement were recorded and quantified within the time intervals typical for APAs and CPAs. Results: Both groups of older adults (non-fallers and fallers) showed higher magnitude of EMG activity in the lateral muscles and increased COP displacement, particularly, during the CPAs time interval when compared to the young group. Older adults, however, were able to change the electrical activity of the muscles during the predictable task by generating APAs with similar magnitudes of those found in young subjects. Conclusions: Compensatory but not anticipatory adjustments are altered in older adults during predict- able lateral postural perturbations. Significance: These findings provide new data on the role of APAs and CPAs in their relationship in older adults during external lateral perturbations and may advance current rehabilitative management strate- gies to improve balance control in older individuals. Ó 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. 1. Introduction When postural balance is perturbed, internally (produced by the person himself) or externally (produced by outside forces), the Central Nervous System (CNS) uses two main types of postural adjustments: anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs). The first mechanism, driven by feed-forward, is associated with the synergic activation of postural muscles and discrete body movements just before a predictable postural perturbation occurs. Their purpose is to min- imize the adverse effects of the disturbance on postural balance (Nashner and McCollum, 1985; Massion, 1992; Aruin and Latash, 1995). The second mechanism, regulated by feedback, deals with the perturbation itself, and entails the coupling of postural muscle activation and movement strategies to restore postural balance after the body disturbance has occurred. This happens with pre- dictable and unpredictable perturbations (Nashner and McCollum, 1388-2457/$36.00 Ó 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinph.2013.02.111 ⇑ Corresponding author. Address: Department of Physical Therapy and Rehabil- itation Sciences, Kansas University Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA. Tel.: +1 913 588 4343; fax: +1 913 588 4568. E-mail address: msantos@kumc.edu (M.J. Santos). Clinical Neurophysiology 124 (2013) 1628–1637 Contents lists available at SciVerse ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph