A modal approach for the soft tissue artefact mathematical representation in optimal joint kinematics estimators

XIII International Symposium on 3D Analysis of Human Movement, LAUSANNE, SUISSE, 14-/07/2014 - 17/07/2014Soft tissue artefact (STA) compensation is the main problem when aiming at optimal bonepose estimate. Given the complexity and specificity of this phenomenon, its compensation can only rely on its general features. This study aims at investigating the effect on joint kinematics estimation of different STA mathematical representations and related degrees of approximation. A modal approach and three different STA definitions (individual marker displacements, MD; marker-cluster geometrical transformations, GT; skin envelope shape variations, SV) were used. Direct measure of thigh and shank STAs from running volunteers, with both skin and pin markers, were used to test which representation and approximation allowed the best improvement of knee kinematics estimate. For both GT and SV definitions, rms errors in knee kinematics were reduced to below 10% of reference rms values, when eleven and fourteen modes were used to approximate thigh and shank STA, respectively