title: Shoulder proprioception: latent muscle reaction times.
abstract: OBJECTIVE
  The purpose of this study was to identify electromyographic (EMG) differences in the latent muscle reaction timing (LMRT) of the rotator cuff between trained overhead throwers and control subjects in response to sudden internal rotation perturbation (P < or = 0.05).
  
  
  METHODS
  Subjects included 15 trained overhead throwers (male intercollegiate baseball players) and 15 untrained subjects (males not active in competitive throwing sports). Subjects were tested while seated, with their dominant glenohumeral joint positioned in 90 degrees abduction/external rotation (scapular plane), their elbow flexed to 90 degrees, and their forearm placed in the perturbation device. Rotator cuff LMRT was assessed as they tried to decelerate a variably timed, sudden internal rotation force. EMG sampling (2000 Hz, 2-s duration) began immediately before perturbation.
  
  
  RESULTS
  Trained throwers had slower infraspinatus (P = 0.011) and teres minor (P = 0.024) LMRT and decreased supraspinatus (P = 0.001) and posterior deltoid (P = 0.0001) muscle activation duration compared with control subjects.
  
  
  CONCLUSIONS
  These results suggest that the rotator cuff muscles of trained throwers may be downregulated in response to sudden internal rotation perturbation. Although these adaptations would enable greater internal rotation velocities during overhead throwing, they may also contribute to glenohumeral joint pathology. The identification of changes in rotator cuff LMRT in response to sudden internal rotation perturbation suggests an area of acquired neuromuscular imbalance warranting consideration by those involved in the rehabilitation and conditioning of the overhead throwing athlete.
authors.affiliation: Section of Sports Medicine, University of Kentucky, Kentucky Clinic, Lexington 40536, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Brindle
authors.forename: J
authors.initials: J
authors.lastname: Nyland
authors.forename: R
authors.initials: R
authors.lastname: Shapiro
authors.forename: D N
authors.initials: DN
authors.lastname: Caborn
authors.forename: R
authors.initials: R
authors.lastname: Stine
mesh_terms: D000293:Adolescent; D000328:Adult; D001265:Athletic Injuries; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D008297:Male; D010465:Perception; D016059:Range of Motion, Articular; D011930:Reaction Time / Q000502:physiology*; D017006:Rotator Cuff / Q000502:physiology*; D012785:Shoulder Joint / Q000473:pathology / Q000502:physiology*