title: Assessing altered motor unit recruitment patterns in paretic muscles of stroke survivors using surface electromyography.
abstract: OBJECTIVE
  The advancement of surface electromyogram (sEMG) recording and signal processing techniques has allowed us to characterize the recruitment properties of a substantial population of motor units (MUs) non-invasively. Here we seek to determine whether MU recruitment properties are modified in paretic muscles of hemispheric stroke survivors.
  
  
  METHODS
  Using an advanced EMG sensor array, we recorded sEMG during isometric contractions of the first dorsal interosseous muscle over a range of contraction levels, from 20% to 60% of maximum, in both paretic and contralateral muscles of stroke survivors. Using MU decomposition techniques, MU action potential amplitudes and recruitment thresholds were derived for simultaneously activated MUs in each isometric contraction.
  
  
  RESULTS
  Our results show a significant disruption of recruitment organization in paretic muscles, in that the size principle describing recruitment rank order was materially distorted. MUs were recruited over a very narrow force range with increasing force output, generating a strong clustering effect, when referenced to recruitment force magnitude. Such disturbances in MU properties also correlated well with the impairment of voluntary force generation.
  
  
  CONCLUSIONS
  Our findings provide direct evidence regarding MU recruitment modifications in paretic muscles of stroke survivors, and suggest that these modifications may contribute to weakness for voluntary contractions.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Hu
authors.forename: Aneesha K
authors.initials: AK
authors.lastname: Suresh
authors.forename: William Z
authors.initials: WZ
authors.lastname: Rymer
authors.forename: Nina L
authors.initials: NL
authors.lastname: Suresh
mesh_terms: D000368:Aged; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D010291:Paresis / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D020521:Stroke / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D017741:Survivors