title: Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball pitchers.
abstract: BACKGROUND
  In a properly coordinated throwing motion, peak pelvic rotation velocity is reached before peak upper torso rotation velocity, so that angular momentum can be transferred effectively from the proximal (pelvis) to distal (upper torso) segment. However, the effects of trunk rotation sequence on pitching biomechanics and performance have not been investigated.
  
  
  OBJECTIVE
  The aim of this study was to investigate the effects of trunk rotation sequence on ball speed and on upper extremity biomechanics that are linked to injuries in high school baseball pitchers. The hypothesis was that pitchers with improper trunk rotation sequence would demonstrate lower ball velocity and greater stress to the joint.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Three-dimensional pitching kinematics data were captured from 72 high school pitchers. Subjects were considered to have proper or improper trunk rotation sequences when the peak pelvic rotation velocity was reached either before or after the peak upper torso rotation velocity beyond the margin of error (±3.7% of the time from stride-foot contact to ball release). Maximal shoulder external rotation angle, elbow extension angle at ball release, peak shoulder proximal force, shoulder internal rotation moment, and elbow varus moment were compared between groups using independent t tests (α < 0.05).
  
  
  RESULTS
  Pitchers with improper trunk rotation sequences (n = 33) demonstrated greater maximal shoulder external rotation angle (mean difference, 7.2° ± 2.9°, P = .016) and greater shoulder proximal force (mean difference, 9.2% ± 3.9% body weight, P = .021) compared with those with proper trunk rotation sequences (n = 22). No other variables differed significantly different between groups.
  
  
  CONCLUSIONS
  High school baseball pitchers who demonstrated improper trunk rotation sequences demonstrated greater maximal shoulder external rotation angle and shoulder proximal force compared with pitchers with proper trunk rotation sequences.
  
  
  CONCLUSIONS
  Improper sequencing of the trunk and torso alter upper extremity joint loading in ways that may influence injury risk. As such, exercises that reinforce the use of a proper trunk rotation sequence during the pitching motion may reduce the stress placed on the structures around the shoulder joint and lead to the prevention of injuries.
authors.affiliation: Department of Kinesiology, Health, and Nutrition, University of Texas San Antonio, San Antonio, Texas, USA Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA sakiko.oyama@utsa.edu.
authors.forename: Sakiko
authors.initials: S
authors.lastname: Oyama
authors.affiliation: Division of Physical Therapy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Yu
authors.affiliation: Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
authors.affiliation: Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Darin A
authors.initials: DA
authors.lastname: Padua
authors.affiliation: Department of Health & Kinesiology, Georgia Southern University, Statesboro, Georgia, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Myers
mesh_terms: D000293:Adolescent; D001484:Baseball / Q000293:injuries / Q000502:physiology*; D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000502:physiology; D005260:Female; D006615:Hip / Q000502:physiology; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D012399:Rotation; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000502:physiology*; D060726:Torso / Q000502:physiology*; D055815:Young Adult; D000092464:Elbow Injuries
keywords: biomechanics; elbow; injury; pitching; shoulder; technique