title: Postural perturbations induced by a moving virtual environment are reduced in persons with brain injury when gripping a mobile object.
abstract: OBJECTIVE
  Gripping a mobile (unfixed) object increases standing postural stability in healthy individuals. We tested whether the same strategy is effective for stabilizing upright posture perturbed by a moving environment (virtual perturbation) in participants with traumatic brain injury (TBI).
  
  
  METHODS
  Fifteen participants with mild-to-moderate postural deficits after TBI and a comparison group of 15 age-matched healthy subjects participated in the study. Participants stood for 1 minute in front of a large screen with a projected three-dimensional image of a boat; for 30 seconds the boat remained stationary (no visual stimulation condition), and for 30 seconds the boat rocked on the water at a speed of 15°/s (visual stimulation condition). The visual stimulation was applied in pseudorandom order (during either the first or second half of the 1-minute trial). To analyze postural stability, the displacement and velocity of the center of mass in the sagittal and frontal planes were compared between groups and across 4 experimental conditions, including standing with/without visual stimulation and with/without gripping a 300-g object (short wooden stick) in the dominant hand.
  
  
  RESULTS
  Participants with TBI showed greater instability under all experimental conditions. The visual stimulation significantly increased postural oscillations in the sagittal plane by 35% to 63% across groups. Gripping a stick significantly reduced the stimulation-induced instability in the sagittal plane by 19% to 29%, although not to the level of the no-stimulation condition in either group.
  
  
  CONCLUSIONS
  The stabilizing effect of gripping an external object in participants with TBI was confirmed. A possibility of using this effect as a balance aid strategy requires further investigation.
authors.affiliation: Department of Physical Therapy, Central Michigan University, Mt Pleasant, Michigan.
authors.forename: Ksenia I
authors.initials: KI
authors.lastname: Ustinova
authors.forename: Debbie J
authors.initials: DJ
authors.lastname: Silkwood-Sherer
mesh_terms: D000328:Adult; D001930:Brain Injuries / Q000503:physiopathology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D055815:Young Adult