title: Shoulder impingement in front-crawl swimming: I. A method to identify impingement.
abstract: OBJECTIVE
  The impingement of subacromial structures has been proposed as a major cause of the shoulder problems experienced by athletes who use repetitive overhead actions. The purpose of this study was to develop a noninvasive method to identify instances at which the shoulder was experiencing impingement during front-crawl swimming.
  
  
  METHODS
  Shoulder impingement has been reported to occur when an arm is: (a) elevated above shoulder height while being rotated internally; and (b) forcibly elevated at, or beyond, the maximum active elevation angle. In this study shoulder configurations that satisfied the above two conditions were sought throughout the functional range of each shoulder; and a boundary that distinguished configurations that would cause shoulder impingement was defined. The shoulder movements exhibited during performance of the front-crawl stroke were measured using three-dimensional videography and compared with the boundary defined for each shoulder. The shoulder was considered to experience impingement if the shoulder configuration observed exceeded the boundary defined for that shoulder.
  
  
  RESULTS
  For a male collegiate swimmer, impingement occurred for 12% of the stroke time for each shoulder.
  
  
  CONCLUSIONS
  The analysis permitted the identification of the instances at which the shoulders were experiencing impingement during the front-crawl swimming. In this study, the measurement of the boundary was based entirely upon the mechanism of impingement described in the literature. Further studies are needed to confirm the occurrence of impingement by means of advanced visualization techniques, such as magnetic resonance imaging (MRI) and ultrasonogram.
authors.affiliation: Department of Exercise Science, University of Iowa, Iowa City, USA. tyanai@pooka.otago.ac.nz
authors.forename: T
authors.initials: T
authors.lastname: Yanai
authors.forename: J G
authors.initials: JG
authors.lastname: Hay
authors.forename: G F
authors.initials: GF
authors.lastname: Miller
mesh_terms: D000174:Acromion / Q000503:physiopathology; D000465:Algorithms; D001132:Arm / Q000503:physiopathology; D012090:Cumulative Trauma Disorders / Q000175:diagnosis / Q000209:etiology; D004551:Elbow Joint / Q000503:physiopathology; D006801:Humans; D006811:Humerus / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology; D015203:Reproducibility of Results; D012399:Rotation; D019534:Shoulder Impingement Syndrome / Q000175:diagnosis / Q000209:etiology*; D012785:Shoulder Joint / Q000503:physiopathology*; D020069:Shoulder Pain / Q000175:diagnosis / Q000209:etiology; D013550:Swimming / Q000293:injuries* / Q000502:physiology; D014743:Videotape Recording