title: Shoulder elevation affects joint position sense and muscle activation differently in upright and supine body orientations.
abstract: OBJECTIVE
  Investigate the effects of shoulder elevation on repositioning errors in upright and supine body orientations, and examine these effects on anterior and posterior deltoid muscle activation. We hypothesized decreased errors, and altered anterior and posterior deltoid activation with increasing elevation, in both orientations.
  
  
  METHODS
  Crossover trial.
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  Thirty-five college-aged participants.
  
  
  METHODS
  Subjects attempted to replicate target positions of various elevation angles in upright and supine body orientations. Also, anterior and posterior deltoid activation was recorded in each shoulder position and body orientation.
  
  
  METHODS
  Vector and variable repositioning errors, anterior and posterior deltoid percentage of maximal contraction.
  
  
  RESULTS
  Vector error was greater in supine compared to upright at 90° and 110°, but not at 70°. Variable error was larger in supine than upright, but was unaffected by elevation. Anterior deltoid activation increased with elevation in the upright posture only. Posterior deltoid activation increased with elevation across postures.
  
  
  CONCLUSIONS
  Muscle activation, external torque, and cutaneous sensations may combine to provide afferent feedback, and be used with centrally-generated signals to interpret the state of the limb during movement. Clinicians may prescribe open kinetic chain exercises in the upright posture with the shoulder elevated approximately 90-100°.
authors.affiliation: Department of Health and Human Development, Western Washington University, United States. Electronic address: David.Suprak@wwu.edu.
authors.forename: David N
authors.initials: DN
authors.lastname: Suprak
authors.affiliation: Department of Health and Human Development, Western Washington University, United States.
authors.forename: Jordan D
authors.initials: JD
authors.lastname: Sahlberg
authors.affiliation: Department of Health and Human Development, Western Washington University, United States.
authors.forename: Gordon R
authors.initials: GR
authors.lastname: Chalmers
authors.affiliation: Department of Health and Human Development, Western Washington University, United States.
authors.forename: Wren
authors.initials: W
authors.lastname: Cunningham
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D057645:Deltoid Muscle / Q000502:physiology*; D005260:Female; D006801:Humans; D007699:Kinesthesis / Q000502:physiology*; D008297:Male; D009043:Motor Activity; D009119:Muscle Contraction / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology; D011187:Posture / Q000502:physiology; D011434:Proprioception / Q000502:physiology; D012782:Shoulder / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*; D016683:Supine Position; D055815:Young Adult
keywords: Kinesthesia; Muscle spindle; Proprioception; Rehabilitation