title: Handball load and shoulder injury rate: a 31-week cohort study of 679 elite youth handball players.
abstract: BACKGROUND
  Knowledge of injury patterns, an essential step towards injury prevention, is lacking in youth handball.
  
  
  OBJECTIVE
  To investigate if an increase in handball load is associated with increased shoulder injury rates compared with a minor increase or decrease, and if an association is influenced by scapular control, isometric shoulder strength or glenohumeral range of motion (ROM).
  
  
  METHODS
  679 players (14-18 years) provided weekly reports on shoulder injury and handball load (training and competition hours) over 31 weeks using the SMS, phone and medical examination system. Handball load in a given week was categorised into (1) <20% increase or decrease (reference), (2) increase between 20% and 60% and (3) increase >60% relative to the weekly average amount of handball load the preceding 4 weeks. Assessment of shoulder isometric rotational and abduction strength, ROM and scapular control was performed at baseline and midseason.
  
  
  RESULTS
  An increase in handball load by >60% was associated with greater shoulder injury rate (HR 1.91; 95% CI 1.00 to 3.70, p=0.05) compared with the reference group. The effect of an increase in handball load between 20% and 60% was exacerbated among players with reduced external rotational strength (HR 4.0; 95% CI 1.1 to 15.2, p=0.04) or scapular dyskinesis (HR 4.8; 95% CI 1.3 to 18.3, p=0.02). Reduced external rotational strength exacerbated the effect of an increase above 60% (HR 4.2; 95% CI 1.4 to 12.8, p=0.01).
  
  
  CONCLUSIONS
  A large increase in weekly handball load increases the shoulder injury rate in elite youth handball players; particularly, in the presence of reduced external rotational strength or scapular dyskinesis.
authors.affiliation: Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Møller
authors.affiliation: Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: R O
authors.initials: RO
authors.lastname: Nielsen
authors.affiliation: Section for Epidemiology, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Attermann
authors.affiliation: Sports medicine clinic, Orthopedic dep., Hospital of Lillebaelt Vejle-Middelfart, Institute of Regional Health Research and Center for Research in Childhood Health, University of Southern Denmark, Odense, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Wedderkopp
authors.affiliation: Division of Sports Traumatology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Lind
authors.affiliation: Section for Sport Science, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Sørensen
authors.affiliation: Oslo Sports Trauma Research Centre, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: G
authors.initials: G
authors.lastname: Myklebust
mesh_terms: D000293:Adolescent; D001265:Athletic Injuries / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D016059:Range of Motion, Articular; D012540:Scapula / Q000503:physiopathology; D000070599:Shoulder Injuries / Q000453:epidemiology*; D012785:Shoulder Joint / Q000503:physiopathology; D013177:Sports; D013997:Time Factors
keywords: Adolescent; Epidemiology; Load; Risk factor; Scapula