title: Inertial measures of motion for clinical biomechanics: comparative assessment of accuracy under controlled conditions - changes in accuracy over time.
abstract: BACKGROUND
  Interest in 3D inertial motion tracking devices (AHRS) has been growing rapidly among the biomechanical community. Although the convenience of such tracking devices seems to open a whole new world of possibilities for evaluation in clinical biomechanics, its limitations haven't been extensively documented. The objectives of this study are: 1) to assess the change in absolute and relative accuracy of multiple units of 3 commercially available AHRS over time; and 2) to identify different sources of errors affecting AHRS accuracy and to document how they may affect the measurements over time.
  
  
  METHODS
  This study used an instrumented Gimbal table on which AHRS modules were carefully attached and put through a series of velocity-controlled sustained motions including 2 minutes motion trials (2MT) and 12 minutes multiple dynamic phases motion trials (12MDP). Absolute accuracy was assessed by comparison of the AHRS orientation measurements to those of an optical gold standard. Relative accuracy was evaluated using the variation in relative orientation between modules during the trials.
  
  
  RESULTS
  Both absolute and relative accuracy decreased over time during 2MT. 12MDP trials showed a significant decrease in accuracy over multiple phases, but accuracy could be enhanced significantly by resetting the reference point and/or compensating for initial Inertial frame estimation reference for each phase.
  
  
  CONCLUSIONS
  The variation in AHRS accuracy observed between the different systems and with time can be attributed in part to the dynamic estimation error, but also and foremost, to the ability of AHRS units to locate the same Inertial frame.
  
  
  CONCLUSIONS
  Mean accuracies obtained under the Gimbal table sustained conditions of motion suggest that AHRS are promising tools for clinical mobility assessment under constrained conditions of use. However, improvement in magnetic compensation and alignment between AHRS modules are desirable in order for AHRS to reach their full potential in capturing clinical outcomes.
authors: Faculty of Medicine and Health Sciences, Orthopedic Service, Department of Surgery, Université de Sherbrooke, Sherbrooke, Quebec, Canada; Research Center on Aging, Sherbrooke, Quebec, Canada; Interdisciplinary Institute for Technological Innovation (3IT), Université de Sherbrooke, Sherbrooke, Quebec, Canada.
authors: Karina
authors: K
authors: Lebel
authors: Faculty of Medicine and Health Sciences, Orthopedic Service, Department of Surgery, Université de Sherbrooke, Sherbrooke, Quebec, Canada; Research Center on Aging, Sherbrooke, Quebec, Canada; Interdisciplinary Institute for Technological Innovation (3IT), Université de Sherbrooke, Sherbrooke, Quebec, Canada.
authors: Patrick
authors: P
authors: Boissy
authors: Research Center on Aging, Sherbrooke, Quebec, Canada.
authors: Mathieu
authors: M
authors: Hamel
authors: Department of Kinesiology, Université du Québec à Montréal, Montreal, Quebec, Canada; Centre de Recherche Institut Universitaire de Gériatrie de Montréal, Montreal, Quebec, Canada.
authors: Christian
authors: C
authors: Duval
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena / Q000502:physiology; D004867:Equipment Design; D006801:Humans; D009068:Movement / Q000502:physiology*; D009949:Orientation / Q000502:physiology