Vol.:(0123456789) 1 3 Exp Brain Res DOI 10.1007/s00221-017-5069-2 RESEARCH ARTICLE Role of point of application of perturbation in control of vertical posture Bing Chen 1  · Yun‑Ju Lee 2  · Alexander S. Aruin 3   Received: 25 March 2017 / Accepted: 17 August 2017 © Springer-Verlag GmbH Germany 2017 outcome highlights the importance of investigation of the role of the point of application of the perturbation. Keywords Postural control · Perturbation · Point of application · Anticipatory · Compensatory · Muscle activation Introduction Many tasks that humans perform in their daily life involve body perturbations. To control vertical posture when dealing with body perturbations, the central nervous system (CNS) uses two main types of adjustments in the activity of trunk and leg muscles. Anticipatory postural adjustments (APAs) control the position of the center of mass of the body (Tous- saint et al. 1997) by activating the trunk and leg muscles prior to a forthcoming body perturbation (Massion 1992), while compensatory postural adjustments (CPAs) serve as a mechanism of restoration of the position of the COM after perturbation has already occurred (Alexandrov et al. 2005). Previous literature suggests that while both, APAs and CPAs participate in postural control, their contribution depends on many factors. Thus, APAs magnitude depends on the direction and magnitude of the forthcoming perturba- tion (Aruin and Latash 1995a, 1996), body stability (Aruin et al. 1998) as well as factors afecting perception of stabil- ity, such as fear of falling (Adkin et al. 2002). It was also suggested that when body stability is reduced (e.g. standing on an unstable board), the CNS considers APAs as an addi- tional perturbation and suppresses APAs to minimize a prob- ability of losing balance (Aruin et al. 1998). On the other hand, when the body instability is not related to the altered base of support (BOS) as it happens, for example when standing wearing rollerskates, APAs may not be afected in Abstract The role of point of application of perturbation in the anticipatory (APAs) and compensatory (CPAs) postural control was studied. Twelve healthy participants stood on a sliding board (that was either locked and as such motion- less or unlocked and as such free to move in the anterior– posterior direction). The body perturbations were applied either to the shoulders (by a pendulum impact) or the feet (by the movement of the sliding board). Electromyographic activity (EMG) of the trunk and lower extremity muscles was recorded. Latencies, integrals of EMG and muscle co- contraction (C) and reciprocal (R) activation indices were calculated and analyzed within the intervals typical for the APAs and CPAs. Higher EMG integrals were seen in the APAs phase when perturbation was applied to the shoulders. Reciprocal activation of muscles was seen in the APAs phase in the shoulders perturbation condition, while co-contraction was seen in the feet perturbation condition. Co-contraction was observed within the CPA phase in both experimental conditions. Higher C values were found in the feet pertur- bation condition in the CPA phase. The results suggest that diferent motor control strategies are employed by the cen- tral nervous system when encounter perturbations of similar magnitude but applied to diferent parts of the body. The * Alexander S. Aruin aaruin@uic.edu 1 PhD Program in Rehabilitation Sciences, College of Applied Health Sciences, University of Illinois, Chicago, IL, USA 2 Department of Industrial Engineering and Engineering Management, National Tsing Hua University, Hsinchu, Taiwan 3 Department of Physical Therapy (MC898), University of Illinois at Chicago, 1919 W. Taylor St, Chicago, IL 60612, USA