title: Inertial measures of motion for clinical biomechanics: comparative assessment of accuracy under controlled conditions - effect of velocity.
abstract: BACKGROUND
  Inertial measurement of motion with Attitude and Heading Reference Systems (AHRS) is emerging as an alternative to 3D motion capture systems in biomechanics. The objectives of this study are: 1) to describe the absolute and relative accuracy of multiple units of commercially available AHRS under various types of motion; and 2) to evaluate the effect of motion velocity on the accuracy of these measurements.
  
  
  METHODS
  The criterion validity of accuracy was established under controlled conditions using an instrumented Gimbal table. AHRS modules were carefully attached to the center plate of the Gimbal table and put through experimental static and dynamic conditions. Static and absolute accuracy was assessed by comparing the AHRS orientation measurement to those obtained using an optical gold standard. Relative accuracy was assessed by measuring the variation in relative orientation between modules during trials.
  
  
  RESULTS
  Evaluated AHRS systems demonstrated good absolute static accuracy (mean error < 0.5(o)) and clinically acceptable absolute accuracy under condition of slow motions (mean error between 0.5(o) and 3.1(o)). In slow motions, relative accuracy varied from 2(o) to 7(o) depending on the type of AHRS and the type of rotation. Absolute and relative accuracy were significantly affected (p<0.05) by velocity during sustained motions. The extent of that effect varied across AHRS.
  
  
  CONCLUSIONS
  Absolute and relative accuracy of AHRS are affected by environmental magnetic perturbations and conditions of motions. Relative accuracy of AHRS is mostly affected by the ability of all modules to locate the same global reference coordinate system at all time.
  
  
  CONCLUSIONS
  Existing AHRS systems can be considered for use in clinical biomechanics under constrained conditions of use. While their individual capacity to track absolute motion is relatively consistent, the use of multiple AHRS modules to compute relative motion between rigid bodies needs to be optimized according to the conditions of operation.
authors.affiliation: 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.forename: Karina
authors.initials: K
authors.lastname: Lebel
authors.forename: Patrick
authors.initials: P
authors.lastname: Boissy
authors.forename: Mathieu
authors.initials: M
authors.lastname: Hamel
authors.forename: Christian
authors.initials: C
authors.lastname: Duval
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology*; D006801:Humans; D009038:Motion; D009068:Movement / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D012399:Rotation