title: Altered force perception in stroke survivors with spastic hemiplegia.
abstract: OBJECTIVE
  To investigate the effect of spasticity and involuntary synergistic activation on force perception during voluntary activation of spastic paretic muscles.
  
  
  METHODS
  Eleven stroke subjects with spastic hemiparesis performed various isometric elbow-flexion force-matching tasks. Subjects were instructed to generate a target reference force with visual feedback using one arm (impaired or non-impaired) and then to produce a force with the other arm to match the magnitude of the reference force without visual feedback. The reference arm was at rest in unilateral exertion trials and maintained contraction in bilateral exertion trials during the matching force-production period.
  
  
  RESULTS
  Both force and effort mismatches occurred in most conditions, and there were asymmetries in force perception. When the non-impaired arm was the matching arm, effort and force overestimation occurred, but effort was matched better than force. When the impaired arm was the matching arm, force underestimation and effort overestimation occurred, but force was matched better than effort. No difference in matching performance was found between unilateral and bilateral exertion-matching tasks.
  
  
  CONCLUSIONS
  Overall, both force and effort misperceptions occur in stroke survivors with spasticity. Spasticity and spastic synergistic activation probably contribute to force and effort misperception during voluntary activation in chronic stroke.
authors.affiliation: Department of Physical Medicine and Rehabilitation, The University of Texas Health Science Center - Houston, Houston, TX, USA.
authors.forename: Jasper T
authors.initials: JT
authors.lastname: Yen
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
mesh_terms: D005260:Female; D006429:Hemiplegia / Q000209:etiology* / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D016059:Range of Motion, Articular; D020521:Stroke / Q000150:complications* / Q000401:mortality; D017741:Survivors