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Technical note: out-of-plane angular correction based on a trigonometric function for use in two-dimensional kinematic studies.

Stevens NJ, Schmitt DO, Cole TM, Chan LK

Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens, Ohio 45701, USA. stevensn@ohio.edu

In two-dimensional (2D) kinematic studies, limb positions in three-dimensional (3D) space observed in lateral view are projected onto a 2D film plane. Elbow and knee-joint angles that are less than 20 degrees out-of-plane of lateral-view cameras generally exhibit very little measurable difference from their 3D counterparts (Plagenhoef 1979 Environment, Behavior, and Morphology; New York: Gustav Fisher, p. 95-118). However, when limb segment angles are more than 20 degrees out-of-plane, as is often the case in locomotor studies of arboreal primates, elbow and knee angles can appear significantly more extended than they actually are. For this reason, a methodology is described that corrects 2D out-of-plane angular estimates using a series of trigonometric transformations.

Published 7 February 2006 in Am J Phys Anthropol, 129(3): 399-402.
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