title: Variability of peak shoulder force during wheelchair propulsion in manual wheelchair users with and without shoulder pain.
abstract: BACKGROUND
  Manual wheelchair users report a high prevalence of shoulder pain. Growing evidence shows that variability in forces applied to biological tissue is related to musculoskeletal pain. The purpose of this study was to examine the variability of forces acting on the shoulder during wheelchair propulsion as a function of shoulder pain.
  
  
  METHODS
  Twenty-four manual wheelchair users (13 with pain, 11 without pain) participated in the investigation. Kinetic and kinematic data of wheelchair propulsion were recorded for 3 min maintaining a constant speed at three distinct propulsion speeds (fast speed of 1.1 m/s, a self-selected speed, and a slow speed of 0.7 m/s). Peak resultant shoulder forces in the push phase were calculated using inverse dynamics. Within individual variability was quantified as the coefficient of variation of cycle to cycle peak resultant forces.
  
  
  RESULTS
  There was no difference in mean peak shoulder resultant force between groups. The pain group had significantly smaller variability of peak resultant force than the no pain group (P<0.01, η²=0.18).
  
  
  CONCLUSIONS
  The observations raise the possibility that propulsion variability could be a novel marker of upper limb pain in manual wheelchair users.
authors.affiliation: Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, 906 S. Goodwin Ave., Urbana, IL 61801, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Moon
authors.forename: C
authors.initials: C
authors.lastname: Jayaraman
authors.forename: I M K
authors.initials: IM
authors.lastname: Hsu
authors.forename: I M
authors.initials: IM
authors.lastname: Rice
authors.forename: E T
authors.initials: ET
authors.lastname: Hsiao-Wecksler
authors.forename: J J
authors.initials: JJ
authors.lastname: Sosnoff
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D009068:Movement / Q000502:physiology*; D012782:Shoulder / Q000502:physiology / Q000503:physiopathology*; D020069:Shoulder Pain / Q000503:physiopathology*; D014910:Wheelchairs; D055815:Young Adult
keywords: Inverse dynamics; Joint kinetics; Movement variability; Pain; Shoulder