Description, Development and Dissemination of Two Consistent Marker-based and Markerless Multibody Models

Abstract

In human movement analysis, multibody models are an indispensable part of the process both for marker-based and video-based markerless approaches. Constituents (segments, joint constraints, body segment inertial parameters etc.) of such models and choice of the modelers play an important role in the accuracy of estimated results (segmental and joint kinematics, segmental and whole-body center of mass positions etc.). For marker-based method, although standard models exist, particularly for the lower extremity (e.g., Conventional Gait Model or models embedded in OpenSim), there seems to be a lack of consolidated explanation on the constituents of the whole-body model. For the markerless approach, multibody kinematic models (e.g., the Theia3D model) have been in use lately. However, there is no clear explanation on the estimated quantities (e.g., joint centers, body surface landmarks etc.) and their relation to the underlying anatomy. This also motivates the need for a description of the markerless multibody model. Moreover, comparing markerless results to those of classical marker-based method is currently the most commonly used approach for evaluation of markerless approaches. This study first aims to develop and describe a whole-body marker-based model ready to be used for human movement analysis. Second, the markerless multibody model embedded in Theia3D is described and inertial parameters are redefined. We also report assessment of the markerless approach compared to marker-based method for a static T-pose performed by 15 subjects. Finally, we disseminate the marker-based and markerless multibody models for their use in Visual3D.

Differences between lower extremity joint running kinetics captured by marker-based and markerless systems were speed dependent

“…In addition, segment COM position and components of the inertia matrix are calculated using segment lengths defined by segment endpoints. 43 Our previously observed joint center differences during the swing phase also help to explain the current results. The hip joint center differences in the anterior–posterior direction were particularly propagated to the extension/flexion HJM.…”

Accuracy of a markerless motion capture system for balance related quantities

“…All these parameters are currently under study in the literature to understand their effect on the accuracy of markerless motion capture [37][38][39]. Another possible limitation is the different approaches used to build marker-based and markerless models [30], which could generate systematic bias. However, we found very small biases for CoM, XCoM and WBAM, suggesting that the models are consistent.…”

“…The participants wore minimal, tightly fitting clothing to allow for appropriate marker placement. They were equipped with a full-body marker set comprising 46 markers [29,30].…”

“…These outputs were exported in Visual3D (C-motion, Germantown, USA, v2021.11.3) and body segment inertial parameters (BSIP – segment mass, position of segment CoM and moment of inertia) were added to the kinematic model according to Dumas and Wojtusch [29]. The markerless and marker-based models are both described in details in [30].…”