title: Acromiohumeral distance and 3-dimensional scapular position change after overhead muscle fatigue.
abstract: BACKGROUND
  Muscle fatigue due to repetitive and prolonged overhead sports activity is considered an important factor contributing to impingement-related rotator cuff pathologic conditions in overhead athletes. The evidence on scapular and glenohumeral kinematic changes after fatigue is contradicting and prohibits conclusions about how shoulder muscle fatigue affects acromiohumeral distance.
  
  
  OBJECTIVE
  To investigate the effect of a fatigue protocol resembling overhead sports activity on acromiohumeral distance and 3-dimensional scapular position in overhead athletes.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Institutional laboratory.
  
  
  METHODS
  A total of 29 healthy recreational overhead athletes (14 men, 15 women; age = 22.23 ± 2.82 years, height = 178.3 ± 7.8 cm, mass = 71.6 ± 9.5 kg).
  
  
  METHODS
  The athletes were tested before and after a shoulder muscle-fatiguing protocol.
  
  
  METHODS
  Acromiohumeral distance was measured using ultrasound, and scapular position was determined with an electromagnetic motion-tracking system. Both measurements were performed at 3 elevation positions (0°, 45°, and 60° of abduction). We used a 3-factor mixed model for data analysis.
  
  
  RESULTS
  After fatigue, the acromiohumeral distance increased when the upper extremity was actively positioned at 45° (Δ = 0.78 ± 0.24 mm, P = .002) or 60° (Δ = 0.58 ± 0.23 mm, P = .02) of abduction. Scapular position changed after fatigue to a more externally rotated position at 45° (Δ = 4.97° ± 1.13°, P < .001) and 60° (Δ = 4.61° ± 1.90°, P = .001) of abduction, a more upwardly rotated position at 45° (Δ = 6.10° ± 1.30°, P < .001) and 60° (Δ = 7.20° ± 1.65°, P < .001) of abduction, and a more posteriorly tilted position at 0°, 45°, and 60° of abduction (Δ = 1.98° ± 0.41°, P < .001).
  
  
  CONCLUSIONS
  After a fatiguing protocol, we found changes in acromiohumeral distance and scapular position that corresponded with an impingement-sparing situation.
authors.affiliation: Rehabilitation Sciences and Physiotherapy, Ghent University, Belgium;
authors.forename: Annelies
authors.initials: A
authors.lastname: Maenhout
authors.forename: Famke
authors.initials: F
authors.lastname: Dhooge
authors.forename: Maarten
authors.initials: M
authors.lastname: Van Herzeele
authors.forename: Tanneke
authors.initials: T
authors.lastname: Palmans
authors.forename: Ann
authors.initials: A
authors.lastname: Cools
mesh_terms: D000328:Adult; D056352:Athletes; D001265:Athletic Injuries / Q000517:prevention & control*; D001530:Belgium; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D012090:Cumulative Trauma Disorders / Q000517:prevention & control*; D005260:Female; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D017006:Rotator Cuff / Q000000981:diagnostic imaging / Q000503:physiopathology; D012540:Scapula / Q000000981:diagnostic imaging / Q000503:physiopathology; D012782:Shoulder / Q000000981:diagnostic imaging / Q000503:physiopathology; D019534:Shoulder Impingement Syndrome / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D013177:Sports; D014463:Ultrasonography
keywords: injury prevention; shoulder; subacromial impingement syndrome; ultrasonography