title: Transition of COM-COP relative phase in a dynamic balance task.
abstract: The purpose of this study was to investigate whether the coordination between center of mass (COM) and center of pressure (COP) could be a candidate collective variable of a dynamical system that captures the organization of the multi-segmental whole body postural control system. We examined the transition of the COM-COP coordination pattern in a moving platform balance control paradigm. 10 young healthy adults stood on a moving surface of support that within a trial was sinusoidally translated in the anterior-posterior direction continuously scaling up and then down its frequency within the range from 0Hz to 3.0Hz. The COP was derived from a single force platform mounted on the moving surface of support. 4 angular joint motions (ankle, knee, hip, and neck) were measured by a 3D motion analysis system that also allowed COM to be derived. The COM-COP coordination changed from in-phase/anti-phase to anti-phase/in-phase at a certain frequency of the support surface, showed hysteresis as a function of the direction of frequency change and higher variability at the transition region. Conversely, the transition of the ankle-hip coordination consistently occurred at 0.3Hz across subjects with little between or within subject variability as a function of transition frequency and before the COM-COP transition. The findings provide evidence that: (1) the transition of the COM-COP coordination pattern is that of a non-equilibrium phase transition with critical fluctuations and hysteresis; and (2) that COM-COP coupling is a candidate collective variable of the multi-segmental whole body postural control system acting on a redundant postural task.
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, USA. Electronic address: cozy1123@gmail.com.
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Ko
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Challis
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, USA.
authors.forename: Karl M
authors.initials: KM
authors.lastname: Newell
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D000886:Anthropometry; D001696:Biomechanical Phenomena; D064368:Healthy Volunteers; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009068:Movement; D009333:Neck / Q000502:physiology; D004856:Postural Balance; D011187:Posture; D011312:Pressure
keywords: Collective variable; Phase transition; Postural control; Self-organization