title: Standing data disproves biomechanical mechanism for balance-based torso-weighting.
abstract: OBJECTIVE
  To test a proposed mechanism for the effect of balance-based torso-weighting (BBTW) in people with multiple sclerosis (MS) and healthy controls. The mechanism to be tested is that application of light weights to the trunk may result in a biomechanical shift of postural sway in the direction of weighting, mechanically facilitating maintenance of the center of mass over the base of support.
  
  
  METHODS
  Nonrandomized controlled trial.
  
  
  METHODS
  Motion analysis laboratory.
  
  
  METHODS
  Participants with MS (n=20; average Expanded Disability Status Scale score, 4.1) and controls matched for sex, age, height, and weight (n=18).
  
  
  METHODS
  Light weights strategically placed according to the BBTW protocol were applied to all participants after at least 3 walking trials and 10 seconds of quiet standing with feet together and eyes open and then eyes closed. Measures were repeated after weighting.
  
  
  METHODS
  Forceplate center of pressure (COP) changes >1 standard error of measurement.
  
  
  RESULTS
  With BBTW, people with MS had larger maximum changes in COP than healthy controls in the left-right direction but not in the anterior-posterior direction. COP changes >1 standard error of measurement occurred in the same direction of weighting 20% of the time (95% confidence interval, 5-34), ranging from 10% to 28% across conditions and directions of postural sway. Direction of greatest weight placement did not match the direction of change in the average COP in most participants with MS or the healthy controls in eyes open or eyes closed conditions (P<.001).
  
  
  CONCLUSIONS
  If BBTW worked via a biomechanical shift of the center of mass, COP changes should match the direction of greatest weighting with BBTW. Our data allowed us to reject this hypothesis. Future research may explore alternative mechanisms of action underlying this intervention.
authors.affiliation: Graduate Program in Physical Therapy, University of California San Francisco/San Francisco State University, San Francisco, CA.
authors.forename: Ajay
authors.initials: A
authors.lastname: Crittendon
authors.affiliation: Graduate Program in Physical Therapy, University of California San Francisco/San Francisco State University, San Francisco, CA.
authors.forename: Danielle
authors.initials: D
authors.lastname: O'Neill
authors.affiliation: Department of Physical Therapy, Samuel Merritt University, Oakland, CA.
authors.forename: Gail L
authors.initials: GL
authors.lastname: Widener
authors.affiliation: Graduate Program in Physical Therapy, University of California San Francisco/San Francisco State University, San Francisco, CA. Electronic address: ddallen@sfsu.edu.
authors.forename: Diane D
authors.initials: DD
authors.lastname: Allen
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D060726:Torso / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*
keywords: BBTW; COP; EC; EDSS; EO; Expanded Disability Status Scale; MS; Multiple sclerosis; Postural balance; Rehabilitation; balance-based torso-weighting; center of pressure; eyes closed; eyes open; multiple sclerosis