title: Shoulder external rotation fatigue and scapular muscle activation and kinematics in overhead athletes.
abstract: BACKGROUND
  Glenohumeral external rotation (GH ER) muscle fatigue might contribute to shoulder injuries in overhead athletes. Few researchers have examined the effect of such fatigue on scapular kinematics and muscle activation during a functional movement pattern.
  
  
  OBJECTIVE
  To examine the effects of GH ER muscle fatigue on upper trapezius, lower trapezius, serratus anterior, and infraspinatus muscle activation and to examine scapular kinematics during a diagonal movement task in overhead athletes.
  
  
  METHODS
  Human performance research laboratory.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Our study included 25 overhead athletes (15 men, 10 women; age = 20 ± 2 years, height = 180 ± 11 cm, mass = 80 ± 11 kg) without a history of shoulder pain on the dominant side.
  
  
  METHODS
  We tested the healthy, dominant shoulder through a diagonal movement task before and after a fatiguing exercise involving low-resistance, high-repetition, prone GH ER from 0° to 75° with the shoulder in 90° of abduction.
  
  
  METHODS
  Surface electromyography was used to measure muscle activity for the upper trapezius, lower trapezius, serratus anterior, and infraspinatus. An electromyographic motion analysis system was used to assess 3-dimensional scapular kinematics. Repeated-measures analyses of variance (phase × condition) were used to test for differences.
  
  
  RESULTS
  We found a decrease in ascending-phase and descending-phase lower trapezius activity (F(1,25) = 5.098, P = .03) and an increase in descending-phase infraspinatus activity (F(1,25) = 5.534, P = .03) after the fatigue protocol. We also found an increase in scapular upward rotation (F(1,24) = 3.7, P = .04) postfatigue.
  
  
  CONCLUSIONS
  The GH ER muscle fatigue protocol used in this study caused decreased lower trapezius and increased infraspinatus activation concurrent with increased scapular upward rotation range of motion during the functional task. This highlights the interdependence of scapular and glenohumeral force couples. Fatigue-induced alterations in the lower trapezius might predispose the infraspinatus to injury through chronically increased activation.
authors.affiliation: University of Sydney, Australia.
authors.forename: Mithun
authors.initials: M
authors.lastname: Joshi
authors.forename: Charles A
authors.initials: CA
authors.lastname: Thigpen
authors.forename: Kevin
authors.initials: K
authors.lastname: Bunn
authors.forename: Spero G
authors.initials: SG
authors.lastname: Karas
authors.forename: Darin A
authors.initials: DA
authors.lastname: Padua
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D056352:Athletes; D001265:Athletic Injuries / Q000503:physiopathology; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology*; D055815:Young Adult