Ultra-dense motion capture algorithm for breast biomechanical modelling in design of sports bras

Abstract

This thesis presents a comprehensive approach to facilitate breast biomechanics research and ergonomic sports bra design. The study involves three main components: dynamic 4D scanning of the female subject during running, dense tracking of breast deformation, and finite element modeling with material properties fine-tuning using 4D scanning data. The innovative use of 4D scanning technology captures whole-surface information of the human body during dynamic activities, providing high-temporal and spatial resolutions mesh data for analysis. Based on the anthropometric landmarks labelled from the 4D scanning sequence, the overall trajectories and the accumulated regional displacement of the breast soft tissues, as well as the distribution of deformation intensity can be precisely analyzed. Results indicated that the accumulated trajectory lengths of different landmarks range from 50 cm to 80 cm. Of which, the vertical and lateral swinging are the primary movement trends of the breasts during running. The large trajectory differences (48.6%) amongst the landmarks also confirm the highly nonlinear deformation patterns of the breasts during dynamic motion. A robust dense tracking method, the Ultra-dense Motion Capture (UdMC) algorithm, is proposed to capture the dense whole-surface deformation profile of the breasts, advancing the traditional motion capture technology from the sparse landmark level to the dense surface level. Comprehensive evaluation shown that our approach significantly outperforms previous works in accuracy, consistency, and efficiency. With reference to the complete 120 fps dataset, the average errors are found as 0.43cm for the control-landmarks and 0.78cm for the non-control (arbitrary) points. As compared to the traditional approach, the calculation speed of the proposed UdMC algorithm is 40-200 times faster. Lastly, a subject-specific finite element (FE) model is constructed and fine-tuned with the dense deformation profile captured by UdMC, making it capable to align with the realistic breast behavior more reliably. To facilitate efficient determination of the subject-specific Mooney-Rivlin material parameters, the principle parameters inflation scheme was proposed to transform the optimization problem from the 5 dimensional space search to the 2 dimensional space search. This FE breasts model has successfully simulated and predicted the characteristics and response of the breasts when wearing different sports bra with varying design factors, which has significant application value in breasts soft tissue biomechanics research as well as validating and optimizing sports bras prototype designs.