title: Individuals with transtibial limb loss use interlimb force asymmetries to maintain multi-directional reactive balance control.
abstract: BACKGROUND
  Deficits in balance control are one of the most common and serious mobility challenges facing individuals with lower limb loss. Yet, dynamic postural balance control among individuals with lower limb loss remains poorly understood. Here we examined the kinematics and kinetics of dynamic balance in individuals with unilateral transtibial limb loss.
  
  
  METHODS
  Five individuals with unilateral transtibial limb loss, and five age- and gender-matched controls completed a series of randomly applied multi-directional support surface translations. Whole-body metrics, e.g. peak center-of-mass displacement and net center-of-pressure displacement were compared across cohorts. Stability margin was computed as the difference between peak center-of-pressure and center-of-mass displacement. Additionally, center-of-pressure and ground reaction force magnitude and direction were compared between the prosthetic, intact, and control legs.
  
  
  RESULTS
  Peak center-of-mass displacement and stability margin did not differ between individuals with transtibial limb loss and controls for all perturbation directions except those loading only the prosthetic leg; in such cases the stability margin was actually larger than controls. Despite similar center-of-mass displacement, greater center-of-pressure displacement was observed in the intact leg during anterior-posterior perturbations, and under the prosthetic leg in medial-lateral perturbations. Further, in the prosthetic leg, ground reaction forces were smaller and spanned fewer directions.
  
  
  CONCLUSIONS
  Deficits in balance control among individuals with transtibial limb loss may be due to their inability to use their prosthetic leg to generate forces that are equal in magnitude and direction to those of unimpaired adults. Targeting this force-generating deficit through technological or rehabilitation innovations may improve balance control.
authors.affiliation: School of Applied Physiology, Georgia Institute of Technology, 555 14th Street NW, Atlanta, GA 30318, United States.
authors.forename: Darren
authors.initials: D
authors.lastname: Bolger
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, 313 Ferst Drive NE, Atlanta, GA 30332-0535, United States.
authors.forename: Lena H
authors.initials: LH
authors.lastname: Ting
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Emory University and Georgia Institute of Technology, 313 Ferst Drive NE, Atlanta, GA 30332-0535, United States. Electronic address: lting@emory.edu.
authors.forename: Andrew
authors.initials: A
authors.lastname: Sawers
mesh_terms: D000328:Adult; D000368:Aged; D000674:Amputees / Q000534:rehabilitation; D001186:Artificial Limbs; D001696:Biomechanical Phenomena / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007866:Leg; D008297:Male; D008875:Middle Aged; D004856:Postural Balance / Q000502:physiology*; D011312:Pressure; D016474:Weight-Bearing / Q000502:physiology*
keywords: Amputee; Artificial limb; Feedback; Ground reaction force; Posture; Stability