title: Reflexive muscle activation alterations in shoulders with anterior glenohumeral instability.
abstract: BACKGROUND
  Patients with glenohumeral instability have proprioceptive deficits that are suggested to contribute to muscle activation alterations.
  
  
  OBJECTIVE
  Muscle activation alterations will be present in shoulders with anterior glenohumeral instability.
  
  
  METHODS
  Posttest-only control group design.
  
  
  METHODS
  Eleven patients diagnosed with anterior glenohumeral instability were matched with 11 control subjects. Each subject received an external humeral rotation apprehension perturbation while reflexive muscle activation characteristics were measured with indwelling electromyography and surface electromyography.
  
  
  RESULTS
  Patients with instability demonstrated suppressed pectoralis major and biceps brachii mean activation; increased peak activation of the subscapularis, supraspinatus, and infraspinatus; and a significantly slower biceps brachii reflex latency. Supraspinatus-subscapularis coactivation was significantly suppressed in the patients with instability as well.
  
  
  CONCLUSIONS
  In addition to the capsuloligamentous deficiency and proprioceptive deficits present in anterior glenohumeral instability, muscle activation alterations are also present. The suppressed rotator cuff coactivation, slower biceps brachii activation, and decreased pectoralis major and biceps brachii mean activation may contribute to the recurrent instability episodes seen in this patient group. Clinicians can implement therapeutic exercises that address the suppressed muscles in patients opting for conservative management or rehabilitation before and after capsulorraphy procedures.
authors.affiliation: Neuromuscular Research Laboratory, UPMC Center for Sports Medicine, University of Pittsburgh, 3200 South Water Street, Pittsburgh, PA 15203, USA. myersjb@msx.upmc.edu
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Myers
authors.forename: Yan-Ying
authors.initials: YY
authors.lastname: Ju
authors.forename: Ji-Hye
authors.initials: JH
authors.lastname: Hwang
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: McMahon
authors.forename: Mark W
authors.initials: MW
authors.lastname: Rodosky
authors.forename: Scott M
authors.initials: SM
authors.lastname: Lephart
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011434:Proprioception / Q000502:physiology*; D012008:Recurrence; D017006:Rotator Cuff / Q000503:physiopathology; D012785:Shoulder Joint / Q000503:physiopathology*