Studies of three-dimensional trajectories of breast movement for better bra design

This paper presents a new method for evaluating 3D breast motion relative to the thorax using a new breast coordinate system. A local virtual origin is defined by four breast boundary points, in a constant relative distance from four bone-fixed thoracic points. The validity and reliability of the method was tested with 11 subjects and confirmed (interclass correlation coefficient = 1.00). The feasibility of the new system was tested with two subjects with pert and ptotic breasts, respectively. Each subject participated in motion experiments whilst treadmill jogging, with and without a sports bra. In the braless motion experiments, the breast movement trajectories of six breast positions resembled a butterfly shape. In a jogging cycle, there was a single anterior and medial peak, and a double peak in the vertical breast displacement. The ptotic breast displacement during jogging was larger and wavy, with a more evident vertical and medial-lateral vibration. It tended to move more medially and anteriorly than the pert breast. The bra trajectories of the subjects wearing sports bras showed that the superior movements of the upper breast need further control. To achieve this, it was proposed that the neckline of the bra should better fit the upper breast boundary.