title: Posture-movement changes following repetitive motion-induced shoulder muscle fatigue.
abstract: Repetitive motion-induced fatigue not only alters local motion characteristics but also provokes global reorganization of movement. However, the three-dimensional (3D) characteristics of these reorganization patterns have never been documented in detail. The goal of this study was to assess the effects of repetitive reaching-induced arm fatigue on the whole-body, 3D biomechanical task characteristics. Healthy subjects (N=14) stood and performed a continuous reaching task (RRT) between two targets placed at shoulder height to fatigue. Whole-body kinematic (Vicon), kinetic (AMTI force platforms) and electromyographic (EMG, Noraxon) characteristics were recorded. Maximal voluntary isometric efforts (MVIE) of the shoulder and elbow were measured pre- and post-RRT. Post-RRT shoulder elevation MVIE was reduced by 4.9+/-8.3% and trapezius EMG amplitude recorded during the RRT increased by 46.9+/-49.9% from the first to last minute of the RRT, indicating that arm fatigue was effectively induced. During fatigued reaching, subjects elevated their shoulder (11.7+/-10.5 mm) and decreased their average shoulder abduction angle by 8.3+/-4.4 degrees. These changes were accompanied by a lateral shift of the body's center of mass towards the non-reaching arm. These findings suggest a compensatory strategy to decrease the load on the fatigued shoulder musculature.
authors.affiliation: Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, Quebec, Canada. jason.fuller@mail.mcgill.ca
authors.forename: Jason R
authors.initials: JR
authors.lastname: Fuller
authors.forename: Karen V
authors.initials: KV
authors.lastname: Lomond
authors.forename: Joyce
authors.initials: J
authors.lastname: Fung
authors.forename: Julie N
authors.initials: JN
authors.lastname: Côté
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001132:Arm / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*