title: Validation of the Inverted Pendulum Model in standing for transtibial prosthesis users.
abstract: BACKGROUND
  Often in balance assessment variables associated with the center of pressure are used to draw conclusions about an individual's balance. Validity of these conclusions rests upon assumptions that movement of the center of pressure is inter-dependent on movement of the center of mass. This dependency is mechanical and is referred to as the Inverted Pendulum Model. The following study aimed to validate this model both kinematically and kinetically, in transtibial prosthesis users and a control group.
  
  
  METHODS
  Prosthesis users (n=6) and matched control participants (n=6) stood quietly while force and motion data were collected under three conditions (eyes-open, eyes-closed, and weight-bearing feedback). Correlation coefficients were used to investigate the relationships between height and excursion of markers and center of masses in mediolateral/anteroposterior-directions, difference between center of pressure and center of mass and the center of mass acceleration in mediolateral/anteroposterior directions, magnitude of mediolateral/anteroposterior-component forces and center of mass acceleration, angular position of ankle and excursion in mediolateral/anteroposterior-directions, and integrated force signals.
  
  
  RESULTS
  Results indicate kinematic validity of similar magnitudes (mean (SD) marker-displacement) between prosthesis users and control group for mediolateral- (r=0.77 (0.17); 0.74 (0.19)) and anteroposterior-directions (r=0.88 (0.18); 0.88 (0.19)). Correlation between difference of center of pressure and center of mass and the center of mass acceleration was negligible on the prosthetic side (r = 0.08 (0.06)) vs. control group (r=-0.51(0.13)).
  
  
  CONCLUSIONS
  Results indicate kinematic validity of the Inverted Pendulum Model in transtibial prosthesis users but kinetic validity is questionable, particularly on the side with a prosthesis.
authors.affiliation: Department of Rehabilitation, School of Health and Welfare, Jönköping University, Box 1026, Jönköping 55111, Sweden. Electronic address: david.rusaw@hhj.hj.se.
authors.forename: David F
authors.initials: DF
authors.lastname: Rusaw
authors.affiliation: Department of Rehabilitation, School of Health and Welfare, Jönköping University, Box 1026, Jönköping 55111, Sweden. Electronic address: simon.ramstrand@hhj.hj.se.
authors.forename: Simon
authors.initials: S
authors.lastname: Ramstrand
mesh_terms: D000328:Adult; D000674:Amputees; D000704:Analysis of Variance; D000843:Ankle Joint / Q000503:physiopathology; D001186:Artificial Limbs; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D006801:Humans; D007700:Kinetics; D007866:Leg; D008297:Male; D008875:Middle Aged; D004856:Postural Balance / Q000502:physiology; D011187:Posture / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*
keywords: Amputee; Balance; Inverted Pendulum Model; Postural control; Transtibial