title: Impaired synergic control of posture in Parkinson's patients without postural instability.
abstract: BACKGROUND
  Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of movement and postural stability.
  
  
  OBJECTIVE
  Multi-muscle synergies stabilizing vertical posture were studied in Parkinson's disease patients without clinical symptoms of postural instability (Hoehn-Yahr ≤ II) and age-matched controls. We tested the hypothesis that both synergy indices during quiet standing and synergy adjustments to self-triggered postural perturbations would be reduced in patients.
  
  
  METHODS
  Eleven Parkinson's disease patients and 11 controls performed whole-body tasks while standing. Surface electromyography was used to quantify synergy indices stabilizing center of pressure shifts in the anterior-posterior direction during a load-release task.
  
  
  RESULTS
  Parkinson's disease patients showed a significantly lower percentage of variance in the muscle activation space accounted for by the first four principal components, significantly reduced synergy indices during steady state, and significantly reduced anticipatory synergy adjustments (a drop in the synergy index prior to the self-triggered unloading).
  
  
  CONCLUSIONS
  The study demonstrates for the first time that impaired synergic control in Parkinson's disease can be quantified in postural tasks, even in patients without clinical manifestations of postural instability. Synergy measurements may provide a biomarker sensitive for early problems with postural stability in Parkinson's disease.
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Ali
authors.initials: A
authors.lastname: Falaki
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA; Department of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Pharmacology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Radiology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Neurosurgery, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Xuemei
authors.initials: X
authors.lastname: Huang
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA; Department of Neurology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA; Department of Pharmacology, Pennsylvania State University-Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Mechelle M
authors.initials: MM
authors.lastname: Lewis
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA. Electronic address: mll11@psu.edu.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Latash
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D010300:Parkinson Disease / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*
keywords: Anticipatory synergy adjustments; Muscle mode; Parkinson's disease; Posture; Synergy