title: Differences in multi-joint kinematic patterns of repetitive hammering in healthy, fatigued and shoulder-injured individuals.
abstract: BACKGROUND
  Work-related musculo-skeletal disorders have been previously related to movement repetition, inadequate postures, non-ergonomic environments, muscular imbalance and fatigue. However, no direct link between fatigue and injury has been experimentally shown. To address this problem, we compared the effects of fatigue and injury on the kinematics of repetitive hammering.
  
  
  METHODS
  Healthy subjects (n=30) hammered repetitively both before and after fatigue. Fatigue was induced by a combination of static and dynamic procedures. Shoulder-injured subjects (n=15) hammered for 30s without fatigue. Kinematics of motion was recorded.
  
  
  RESULTS
  The movement time and shoulder range of motion during hammering were not affected by either fatigue or shoulder injury. When fatigued, the healthy subjects displayed decreased range of joint motion, peak velocity and peak acceleration of elbow motion during hammering as well as reduced grip strength. Shoulder-injured individuals had a smaller hammer trajectory amplitude than healthy controls with or without fatigue. They also had lower wrist range of motion, elbow peak velocity, and peak wrist and elbow acceleration compared to healthy subjects hammering without fatigue but only lower wrist peak acceleration compared to healthy subjects hammering with fatigue.
  
  
  CONCLUSIONS
  Results showed that fatigue affects elbow motion while shoulder injury affects both wrist and elbow motions during hammering. However, shoulder kinematics were not changed by either fatigue or shoulder injury. These changes at the wrist and elbow may reflect strategies used by individuals with shoulder injury to maintain constant movement duration and shoulder kinematics during movement.
authors.affiliation: Center for Interdisciplinary Research in Rehabilitation of Montreal (CRIR), Canada; Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, Que., Canada H2W 1S4. julie.cote2@mcgill.ca
authors.forename: Julie N
authors.initials: JN
authors.lastname: Côté
authors.forename: Denis
authors.initials: D
authors.lastname: Raymond
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Mathieu
authors.forename: Anatol G
authors.initials: AG
authors.lastname: Feldman
authors.forename: Mindy F
authors.initials: MF
authors.lastname: Levin
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000502:physiology*; D013647:Task Performance and Analysis; D014955:Wrist Joint / Q000502:physiology*