Accuracy of digitization using automated and manual methods

Background and Purpose. 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 interseg mental angles during pendular motion at varying speeds and (2) to determine changes in accuracy introduced by autodigitization and digitization by exp erienced manual raters. Methods. Angular speed of a T-shaped pendulum was s ystematically increased by releasing the pendulum from 4 angles (0 degrees [no movement], 45 degrees, 90 degrees, and 120 degrees). Twelve reference a ngles 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 erro r for the autodigitized trials was larger than that for the manually digiti zed trials. For the autodigitized trials, the static trials (release positi on =0 degrees) produced less mean error than the trials with movement produ ced. The ICCs showed a high degree of consistency among all raters, ranging from .707 to .999. Conclusion and Discussion. Our findings support the con clusion that under carefully controlled conditions, a 3-D motion measuremen t system can produce clinically acceptable measurements of accuracy across a range of angular speeds. Furthermore, acceptable accuracy is possible reg ardless of the digitization method.