title: Compensatory strategies during manual wheelchair propulsion in response to weakness in individual muscle groups: A simulation study.
abstract: BACKGROUND
  The considerable physical demand placed on the upper extremity during manual wheelchair propulsion is distributed among individual muscles. The strategy used to distribute the workload is likely influenced by the relative force-generating capacities of individual muscles, and some strategies may be associated with a higher injury risk than others. The objective of this study was to use forward dynamics simulations of manual wheelchair propulsion to identify compensatory strategies that can be used to overcome weakness in individual muscle groups and identify specific strategies that may increase injury risk. Identifying these strategies can provide rationale for the design of targeted rehabilitation programs aimed at preventing the development of pain and injury in manual wheelchair users.
  
  
  METHODS
  Muscle-actuated forward dynamics simulations of manual wheelchair propulsion were analyzed to identify compensatory strategies in response to individual muscle group weakness using individual muscle mechanical power and stress as measures of upper extremity demand.
  
  
  RESULTS
  The simulation analyses found the upper extremity to be robust to weakness in any single muscle group as the remaining groups were able to compensate and restore normal propulsion mechanics. The rotator cuff muscles experienced relatively high muscle stress levels and exhibited compensatory relationships with the deltoid muscles.
  
  
  CONCLUSIONS
  These results underline the importance of strengthening the rotator cuff muscles and supporting muscles whose contributions do not increase the potential for impingement (i.e., the thoracohumeral depressors) and minimize the risk of upper extremity injury in manual wheelchair users.
authors.affiliation: Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Slowik
authors.affiliation: Department of Biomedical Engineering, The University of Southern California, Los Angeles, CA, USA; Department of Biological Sciences, The University of Southern California, Los Angeles, CA, USA.
authors.forename: Jill L
authors.initials: JL
authors.lastname: McNitt-Gray
authors.affiliation: Pathokinesiology Laboratory, Rancho Los Amigos National Rehabilitation Center, Downey, CA, USA; Rehabilitation Engineering, Rancho Los Amigos National Rehabilitation Center, Downey, CA, USA.
authors.forename: Philip S
authors.initials: PS
authors.lastname: Requejo
authors.affiliation: Pathokinesiology Laboratory, Rancho Los Amigos National Rehabilitation Center, Downey, CA, USA.
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Mulroy
authors.affiliation: Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA. Electronic address: rneptune@mail.utexas.edu.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Neptune
mesh_terms: D000328:Adult; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018908:Muscle Weakness / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000293:injuries / Q000502:physiology*; D010264:Paraplegia / Q000534:rehabilitation; D012307:Risk Factors; D034941:Upper Extremity / Q000293:injuries / Q000502:physiology*; D014910:Wheelchairs; D055815:Young Adult
keywords: Biomechanics; Forward dynamics simulation; Muscle fatigue; Muscle weakness; Musculoskeletal model; Wheelchair propulsion