Study On Dynamic Comfort And Design Of Sports Bras

Breast displacement of a female body during exercise might cause discomfort, breast pain and even other injury to breast tissue. Sports bras usually tight-fit and made of elastic materials are used to provide firm support to the breast and reduce the displacement. The tension caused by stretched fabrics provides the breast support through compression which might cause another problem, pressure discomfort. The different design of sports bra in terms of materials and styles might have various effects on the breast support both in static and dynamic states.The purpose of this study is to develop method to evaluate dynamic and pressure comfort of sports bra, and investigate mechanical properties of the materials on function of sports bra. Six healthy, active, young females of breast size 75 B volunteered to participate in the experiment of running and vertical jump in this study. Three types of sports bras were used, a normal bra(bra A), one with a cup shape but no pad inside(bra NC) and one with a cup shaped pad inserted into the cup(bra C). The 3D breast displacements of subjects in four conditions(bare, bra A, bra C, and bra NC) were respectively recorded at five points including left nipple and four surrounding points by using an 8-camera Vicon motion capturing system. Relative displacement of the breast was then calculated through transforming the Global Coordinate Transformation(GCS) to a Breast Coordinate Transformation(BCS) established at a virtual origin inside the left breast. The pressure at the five points was also measured by using air pack pressure sensors. Material mechanical properties(fabrics and padding materials) were tested by biaxial extension and thickness compression measurement.The following results were obtained by analyzing data of relative displacement and pressure fluctuations, combined with the mechanical properties of materials.(1) The largest displacement occurred in the vertical direction(up to 60mm), and the displacement of anterior-posterior(AP) direction and medial-lateral(ML) direction is relatively small(less than 30mm), while displacement of ML direction was bigger than AP direction during running. Compared with bared condition, wearing bra could support the breast and obviously reduced breast displacements(up to 45 mm in vertical direction), bra C seemed to be more effective in reducing the displacement.(2) Wearing bra, the maximum pressure was usually at the point 5 cm below nipple(up to 1.4k Pa), and the minimum pressure was usually at the point 5 cm upper nipple(less than 0.95 k Pa). Compared with bra NC, the pressure of bra C was significantly increased about 0.2k Pa. The breast movement caused extra pressure on the breast(up to 0.76 k Pa).(3) The tension caused by stretched fabrics and padding provides the breast support and compression: the greater the elastic modulus was, and the greater the tensile stress produced. The elastic modulus of fabric of sports bra was around 2N? m-1, and padding material around 3N?m-1. Pressure on bra by breast caused compression in thickness direction of padding materials and reduce dynamic breast displacement. Therefore, to increase compressible thickness of padding material could help damping effect of sports bra.