title: Alteration of the foot center of pressure trajectory by an unstable shoe design.
abstract: BACKGROUND
  Unstable sole designs have been used as functional or therapeutic tools for improving body stability during locomotion. It has been suggested that the narrow base of support under the feet generate perturbations that challenge the instability of different joints during motion, thereby forcing the body to modify its movement in order to maintain a stable gait. The purpose of the present study was to explore the correlation between the stability of the footwear-device and the magnitude of perturbation conveyed during gait.
  
  
  METHODS
  Various levels of dynamic instability were achieved using a novel foot-worn platform with two adjustable convex rubber elements attached to its sole. A total of 20 healthy male adults underwent direct in-shoe pressure measurements while walking with the footwear device. Foot center of pressure (COP) and stride to stride variability measures were extracted to examine the correlation between the magnitude of the instability and the imposed perturbations during gait.
  
  
  RESULTS
  A counterintuitive but significant correlation was found between stride to stride variability and the instability of the biomechanical elements. Moreover, there was significant correlation between the instability of the elements and the perturbations found in the COP trajectory. The linear model describing this correlation was found to be statistically significant.
  
  
  CONCLUSIONS
  There was significantly negative correlation between the level of instability induced by the shoe design and the amount of perturbations conveyed during gait. This suggests that the external perturbation must remain within a certain range limit. Exceeding this limit can negatively affect the treatment and probably lead to opposite results.
authors.affiliation: Biorobotics and Biomechanics Lab (BRML), Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel.
authors.forename: Mona
authors.initials: M
authors.lastname: Khoury
authors.affiliation: Biorobotics and Biomechanics Lab (BRML), Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel ; Division of Orthopedics, Sourasky Medical Center, Tel Aviv, Israel.
authors.forename: Amir
authors.initials: A
authors.lastname: Haim
authors.affiliation: Department of Orthopedics and Talpiot Medical Leadership Program, Sheba Medical Center, Tel Aviv, Israel.
authors.forename: Amir
authors.initials: A
authors.lastname: Herman
authors.affiliation: Department of Orthopaedic Surgery, Ha'Emek Medical Center, Afula, Israel.
authors.forename: Nimrod
authors.initials: N
authors.lastname: Rozen
authors.affiliation: Biorobotics and Biomechanics Lab (BRML), Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel.
authors.forename: Alon
authors.initials: A
authors.lastname: Wolf
keywords: Foot center of pressure; Gait; Plantar pressures; Unstable shoe design