title: Spasticity, weakness, force variability, and sustained spontaneous motor unit discharges of resting spastic-paretic biceps brachii muscles in chronic stroke.
abstract: BACKGROUND
  The purpose of our study was to examine relations among spasticity, weakness, force variability, and sustained spontaneous motor unit discharges in spastic-paretic biceps brachii muscles in chronic stroke.
  
  
  METHODS
  Ten chronic stroke subjects produced submaximal isometric elbow flexion force on impaired and non-impaired sides. Intramuscular EMG (iEMG) was recorded from biceps and triceps brachii muscles.
  
  
  RESULTS
  We observed sustained spontaneous motor unit discharges in resting biceps on iEMG. Spontaneous discharges increased after voluntary activation only on the impaired side. The impaired side had greater matching errors and greater fluctuations in isometric force. Spontaneous discharges were not related functionally to spasticity, force variability, or weakness. However, greater strength on the impaired side correlated with less force variability.
  
  
  CONCLUSIONS
  Weakness rather than spasticity is a main factor interfering with voluntary force control in paretic-spastic biceps brachii muscles in chronic stroke.
authors.affiliation: Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center at Houston (UTHealth), Houston, Texas, USA.
authors.forename: Shuo-Hsiu
authors.initials: SH
authors.lastname: Chang
authors.forename: Gerard E
authors.initials: GE
authors.lastname: Francisco
authors.forename: Ping
authors.initials: P
authors.lastname: Zhou
authors.forename: W Zev
authors.initials: WZ
authors.lastname: Rymer
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
mesh_terms: D000200:Action Potentials / Q000502:physiology; D002908:Chronic Disease; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009128:Muscle Spasticity / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D053580:Muscle Strength / Q000502:physiology; D018908:Muscle Weakness / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D020521:Stroke / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*