This work describes the kinematic laws that govern the transmission of soft tissue artifact errors to kinematic variables in the analysis of human movements. Artifacts are described as relative translations and rotations of the marker cluster over the bone, and a set of explicit expressions is defined to account for the effect of that relative motion on different representations of rotations: the rotation around the screw axis, or rotation vector, and three Euler angle sequences (XY′Z, YX′Y″, ZX′Y″). Although the error transmission is nonlinear in all cases, the effect of artifacts is greater on Euler sequences than on the rotation vector. Specifically, there are crosstalk effects in Euler sequences that amplify the errors near singular configurations. This fact is an additional source of variability in studies that describe artifacts by comparing the Euler angles obtained from skin markers, with the angles of an artifact-free gold standard. The transmission of errors to rotation vector coordinates is less variable or dependent on the type of motion. This model has been tested in an experiment with a deformable mechanical model with a spherical joint.
Model of Soft Tissue Artifact Propagation to Joint Angles in Human Movement Analysis
Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received April 12, 2013; final manuscript received November 26, 2013; accepted manuscript posted December 12, 2013; published online February 13, 2014. Assoc. Editor: Zong-Ming Li.
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Page, Á., de Rosario, H., Mata, V., and Besa, A. (February 13, 2014). "Model of Soft Tissue Artifact Propagation to Joint Angles in Human Movement Analysis." ASME. J Biomech Eng. March 2014; 136(3): 034502. https://doi.org/10.1115/1.4026226
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