title: Change in glenohumeral rotation and scapular position after competitive high school baseball.
abstract: BACKGROUND
  Pathologies such as anterior instability and impingement are common in baseball and have been linked to decreases in internal rotation (IR) and concurrent increases in external rotation (ER). In addition, alterations to scapular position have been identified in this population, but the chronology of these adaptations is uncertain.
  
  
  OBJECTIVE
  To determine whether there is a change in range of motion and scapular position after a single baseball season.
  
  
  METHODS
  Prospective cohort.
  
  
  METHODS
  High school.
  
  
  METHODS
  19 high school baseball players (age 16.6 +/- 0.8 y, mass 78.6 +/- 12.0 kg, height 180.3 +/- 6.2 cm).
  
  
  METHODS
  Subjects were measured for all dependent variables at preseason and postseason.
  
  
  METHODS
  Participants were measured for glenohumeral (GH) IR and ER with the scapula stabilized. Total GH range of motion was calculated as the sum of IR and ER. Scapular upward rotation was measured at 0 degrees, 60 degrees, 90 degrees, and 120 degrees of GH abduction in the scapular plane, and scapular protraction, at 0 degrees, hands on hips, and 90 degrees of GH abduction.
  
  
  RESULTS
  Overall, the dominant arm had significantly less GH IR (11.4 degrees, P = .005) and significantly more ER (4.7 degrees, P = .001) than the nondominant arm. Total motion in the dominant arm was significantly less than in the nondominant arm (6.7 degrees, P = .001). Scapular upward rotation in the dominant arm significantly increased at 0 degrees (2.4 degrees, P = .002) and significantly decreased at 90 degrees (3.2 degrees, P = .001) and 120 degrees (3.2 degrees, P < .001) of abduction from preseason to postseason. Scapular protraction in the nondominant arm significantly decreased at 45 degrees (0.32 cm, P = .017) and 90 degrees (0.33 cm, P = .006) from preseason to postseason.
  
  
  CONCLUSIONS
  These data suggest that scapular adaptations may be acquired over a relatively short period (12 wk) in a competitive baseball season. Competitive high school baseball players also presented with significant GH motion differences between their dominant and nondominant arms. Total motion was also significantly less in the dominant arm than in the nondominant arm.
authors.affiliation: McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Thomas
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Swanik
authors.forename: Charles
authors.initials: C
authors.lastname: Swanik
authors.forename: Kellie C
authors.initials: KC
authors.lastname: Huxel
authors.forename: John D
authors.initials: JD
authors.lastname: Kelly
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001265:Athletic Injuries / Q000209:etiology / Q000517:prevention & control; D001484:Baseball / Q000293:injuries / Q000502:physiology*; D001696:Biomechanical Phenomena; D003163:Competitive Behavior; D006801:Humans; D008297:Male; D011187:Posture; D011446:Prospective Studies; D016059:Range of Motion, Articular; D012307:Risk Factors; D012399:Rotation; D012540:Scapula / Q000293:injuries / Q000502:physiology*; D012574:Schools; D019534:Shoulder Impingement Syndrome / Q000209:etiology / Q000517:prevention & control; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000502:physiology*; D013223:Statistics as Topic; D013997:Time Factors