The Stochastic Component of the Postural Sway Variability is Higher in Children with Balance Impairments
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The Stochastic Component of the Postural Sway Variability is Higher in Children with Balance Impairments MAX J. KURZ, DAVID J. ARPIN, BRENDA L. DAVIES, and REGINA HARBOURNE Department of Physical Therapy, Munroe-Meyer Institute for Genetics and Rehabilitation, University of Nebraska Medical Center, 985540 Nebraska Medical Center, Omaha, NE 68198-5450, USA (Received 5 December 2012; accepted 29 April 2013; published online 4 May 2013) Associate Editor Thurmon E. Lockhart oversaw the review of this article.
system to correct the sway of the body to remain within the base of support.1,2 The amount and nature of the variability in the static postural sway pattern has received considerable attention because it appears to be related to both the sensorimotor integration process and afferent information received from the periphery.11,23,24,26,27 While removal of visual information is known to increase the amount of postural sway variability (as measured by the standard deviation),11,26,27,35 the source of this increased variability is unclear. It has been suggested that the increased amount of variability represents inefficiencies in properly selecting a motor output that will adjust the postural sway when the visual feedback is removed. These postural adjustments are referred to as deterministic because they are intentional adjustment in the motor command that result in a specific and expected adjustment in the postural sway. It has been alternatively suggested that changes in the postural sway variability may also arise from nondeterministic or stochastic processes that permeate every level of the neuromuscular system.8,9,23,24 For example, it has been shown that there are random errors in the release of neurotransmitters at the neuromuscular junction and recruitment of the motor units.12 These subtle changes create stochastic changes in the timing and force production of the muscle.7,20,22 Furthermore, it has been demonstrated that there is noise in the transduction of the sensory feedback, which can be problematic if the noise is equal to or greater than the sensory information.12 It has been suggested that the nervous system attempts to overcome this problem by relying more on sensory feedback that has less stochastic features. However, when the more reliable sensory information is removed (such as vision), the nervous system is forced to use alternative sensory information that may have greater stochastic features. Effectively, these stochastic pro-
Abstract—Children with balance impairments have an increased amount of variability in the sway of the center of pressure (COP) during standing. Limited efforts have been made to quantify the nature of the variability. This exploratory investigation examined the deterministic and stochastic features that comprise the time-dependent postural sway variability during standing. We measured the COP in standing of a heterogeneous group of children with balance impairments and an age-matched cohort of typically developing children, both with and without vision. The standard deviati
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