Ground reaction: intrinsic and extrinsic variability assessment and related method for artefact treatment

Ground reaction (GR) components measured by a dynamometric platform represe nt the dynamic interaction of the moving human body with the ground and dep end on the subject-platform relative position and orientation. The observed variability among the GR measurements of the walking trials of an individu al is either due to variability in the motor performance (intrinsic variabi lity) or due to changes in the direction of walking acid in the position an d orientation of the striking foot relative to the platform (extrinsic vari ability). A method, based on the median operator, is presented here which l ets us quantify the two components of variability. The application of the m ethod to a large data set of normal subjects evidenced changes in progressi on direction/foot orientation (95th percentile value is 6.9 degrees), which can dramatically change the patterns of GR components. This result warns a bout improper analysis of ground reaction measurement. An algorithm for res toring GR measurements affected by artefact was derived from the above meth od. This tool can be of valuable aid in clinical practice where patients' c onditions suggest to not insist on repetition of trials even if the require d number of correct foot placements has not been achieved. The artefact cor rection algorithm has been applied to a large data set artificially corrupt ed to evaluate its robustness. (C) 2001 Elsevier Science Ltd. All rights re served.