title: Analysis of interactive effect of stretch reflex and shortening reaction on rigidity in Parkinson's disease.
abstract: OBJECTIVE
  To examine the correlation between rigidity and interaction of stretch reflex and shortening reaction during passive movements of the wrist and to compare this correlation with that between rigidity and stretch reflex alone.
  
  
  METHODS
  Twelve subjects with Parkinson's disease participated in the study in Off-medication and On-medication states. A servomotor imposed wrist flexion and extension within +/-30 degrees at velocities 50 and 280 degrees/s, while joint torque and EMG of the wrist flexors and extensors were recorded. Rigidity was quantified by integrating torque with joint angle, i.e., objective rigidity (OR) score, for extension and flexion, respectively. The interaction between EMG responses was estimated by calculating a ratio of normalized EMG in stretched to shortened muscles for both movements.
  
  
  RESULTS
  The OR scores were more strongly correlated with the EMG ratios than with EMG of the stretched muscles alone. The strongest and significant correlation was found between the OR score and EMG ratio during the extension at high velocity in the Off-medication (r=0.792, p=0.002).
  
  
  CONCLUSIONS
  Both stretch reflex and shortening reaction are important determinants of rigidity.
  
  
  CONCLUSIONS
  Study findings provide new insight into mechanistic descriptions of rigidity and have implications for development and evaluation of interventions.
authors.affiliation: Rehabilitation Science Research Laboratory, Department of Physical Therapy, Creighton University, Omaha, NE 68178, USA. RuiPingXia@creighton.edu
authors.forename: Ruiping
authors.initials: R
authors.lastname: Xia
authors.forename: Junfeng
authors.initials: J
authors.lastname: Sun
authors.forename: A Joseph
authors.initials: AJ
authors.lastname: Threlkeld
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000494:pharmacology / Q000627:therapeutic use; D015259:Dopamine Agents / Q000494:pharmacology / Q000627:therapeutic use; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009127:Muscle Rigidity / Q000188:drug therapy / Q000503:physiopathology*; D010300:Parkinson Disease / Q000188:drug therapy / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000187:drug effects / Q000502:physiology; D012026:Reflex, Stretch / Q000187:drug effects / Q000502:physiology*; D019415:Torque; D016896:Treatment Outcome; D014955:Wrist Joint / Q000503:physiopathology
chemical_list: D000978:Antiparkinson Agents; D015259:Dopamine Agents