title: The rotator cuff muscles are activated at low levels during shoulder adduction: an experimental study.
abstract: OBJECTIVE
  During isometric shoulder adduction in normal subjects, do the rotator cuff muscles activate more than other shoulder muscles? Are the activation patterns influenced by shoulder abduction angle or load?
  
  
  METHODS
  A within-participant, repeated measures experimental study.
  
  
  METHODS
  15 healthy adults.
  
  
  METHODS
  Participants performed an isometric adduction exercise at 30°, 60°, and 90° abduction in the scapular plane and at 25%, 50%, 75%, and 100% load.
  
  
  METHODS
  During the exercises, a combination of indwelling and surface electromyographic recordings were taken from 11 shoulder muscles: supraspinatus, infraspinatus, subscapularis, pectoralis major, teres major, latissimus dorsi, rhomboid major, serratus anterior, lower trapezius, upper trapezius, and deltoid.
  
  
  RESULTS
  At 100% load, mean rotator cuff activation levels were low (supraspinatus at 3% of its maximum voluntary contraction, infraspinatus 27%, and subscapularis 27%) and significantly less than the activation levels of rhomboid major (81%), latissimus dorsi (103%), and teres major (76%) (F₁₀,₁₄₀ = 15.5, p < 0.01). No significant difference in activity levels of the rotator cuff muscles were recorded when isometric adduction was performed at 30°, 60°, or 90° abduction (p > 0.89). Among the muscles activated above minimum levels (> 10% of maximum voluntary contraction), mean activation levels increased as load increased (F₃,₄₂ = 72.0, p < 0.01)
  
  
  CONCLUSIONS
  Since isometric adduction in normal subjects does not produce moderate to high activation levels in any of the rotator cuff muscles tested, these results do not support the use of shoulder adduction to identify rotator cuff muscle dysfunction or strengthen the rotator cuff muscles.
authors.affiliation: The University of Sydney, Australia. darren.reed@sydney.edu.au
authors.forename: Darren
authors.initials: D
authors.lastname: Reed
authors.forename: Mark
authors.initials: M
authors.lastname: Halaki
authors.forename: Karen
authors.initials: K
authors.lastname: Ginn
mesh_terms: D000293:Adolescent; D000328:Adult; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D017006:Rotator Cuff / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology; D055815:Young Adult