title: Nonlinear analysis of sitting postural sway indicates developmental delay in infants.
abstract: BACKGROUND
  Upright sitting is one of the first developmental motor milestones achieved by infants, and sitting postural sway provides a window into the developing motor control system. A variety of posture sway measures can be used, but the optimal measures for infant development have not been identified.
  
  
  METHODS
  We have collected sitting postural sway data from two groups of infants, one with typical development (n=33), and one with delayed development and either diagnosed with or at risk for cerebral palsy (n=26), when the infants had developed to the point where they could just maintain sitting for about 10s. Postural sway data was collected while infants were sitting on a force platform, and the center of pressure was analyzed using both linear and nonlinear measures.
  
  
  RESULTS
  Our results showed that a nonlinear measure, the largest Lyapunov exponent, was the only parameter of postural sway that revealed significant differences between infants with typical versus delayed development. The largest Lyapunov exponent was found to be higher for typically developing infants, indicating less repeated patterning in their movement coordination.
  
  
  CONCLUSIONS
  A nonlinear measure such as largest Lyapunov exponent may be useful as an identifier of pathology and as a yardstick for the success of therapeutic interventions.
authors.affiliation: Biomechanics Laboratory, University of Nebraska at Omaha, Omaha, NE, USA.
authors.forename: Joan E
authors.initials: JE
authors.lastname: Deffeyes
authors.forename: Regina T
authors.initials: RT
authors.lastname: Harbourne
authors.forename: Anastasia
authors.initials: A
authors.lastname: Kyvelidou
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Stuberg
authors.forename: Nicholas
authors.initials: N
authors.lastname: Stergiou
mesh_terms: D000465:Algorithms; D002547:Cerebral Palsy / Q000175:diagnosis* / Q000503:physiopathology*; D002658:Developmental Disabilities / Q000175:diagnosis* / Q000503:physiopathology*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009068:Movement; D017711:Nonlinear Dynamics; D004856:Postural Balance; D011187:Posture