title: Accuracy of digitization using automated and manual methods.
abstract: OBJECTIVE
  Computerized 3-dimensional (3-D) motion measurement systems are used by those interested in human motion. The purposes of this study were (1) to determine the limits of accuracy in determining intersegmental angles during pendular motion at varying speeds and (2) to determine changes in accuracy introduced by autodigitization and digitization by experienced manual raters.
  
  
  METHODS
  Angular speed of a T-shaped pendulum was systematically increased by releasing the pendulum from 4 angles (0 degrees [no movement], 45 degrees, 90 degrees, and 120 degrees). Twelve reference angles calculated from markers placed on the pendulum were estimated over 20 frames for 10 trials at each release position.
  
  
  RESULTS
  Mean errors across trials and frames for intersegmental angles reconstructed by a 3-D motion measurement system were within +/- 1 degree across all release positions. An analysis of variance and a post hoc Tukey test revealed that the mean error for the autodigitized trials was larger than that for the manually digitized trials. For the autodigitized trials, the static trials (release position=0 degrees) produced less mean error than the trials with movement produced. The ICCs showed a high degree of consistency among all raters, ranging from .707 to .999.
  
  
  CONCLUSIONS
  Our findings support the conclusion that under carefully controlled conditions, a 3-D motion measurement system can produce clinically acceptable measurements of accuracy across a range of angular speeds. Furthermore, acceptable accuracy is possible regardless of the digitization method.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Howard A Rusk Rehabilitation Center, University of Missouri-Columbia, 65212, USA. dan_wilson@pmr.missouri.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Wilson
authors.forename: B K
authors.initials: BK
authors.lastname: Smith
authors.forename: J K
authors.initials: JK
authors.lastname: Gibson
authors.forename: B K
authors.initials: BK
authors.lastname: Choe
authors.forename: B C
authors.initials: BC
authors.lastname: Gaba
authors.forename: J T
authors.initials: JT
authors.lastname: Voelz
mesh_terms: D005684:Gait; D006801:Humans; D007091:Image Processing, Computer-Assisted; D026741:Physical Therapy Modalities / Q000295:instrumentation*; D012015:Reference Standards; D014741:Video Recording