Ergonomic design of supportive moulded bras

Abstract

Breasts are mainly composed of soft tissues, which allow them to move freely over the pectoral fascia. Bras are a key external form of support for breasts. Without the adequate support of bras, excessive body movement results in large forces onto the breast skin, thus leading to the over-stretching of the breast tissues and related breast pain, and even an increase in sagging in the breast area. Permanent deformation of the breast structure could even be a possibility because of repeated high loads on the breasts. As compared against traditional cut-and-sewn bras, the smoothly moulded bras provide better shape, comfort, handfeel and support. However, there has been limited knowledge about the support features of moulded bras with differences in the material of shoulder straps, bra band and underwires, as well as the combined effect of bra components towards the bra support and bra-skin pressure. In this study, the overall aim is to evaluate the support features of moulded bras and the corresponding pressure comfort to improve the ergonomic design of moulded bras. To fill the knowledge gaps in the traditional bra design process, the bra-skin pressure and the support function of moulded bras in term of vertical breast displacement were investigated. The effects of bra cup material, bra strap, underband and underwires on bra-skin pressure and breast displacement were systematically assessed by using the NOVEL Pliance-X® pressure system and the VICON motion capture system respectively. Bra conditions were examined with the change in length or material of shoulder strap and bra band, cup materials and underwire insertion. To minimize the discrepancies of human wear trials, a soft manikin with 75D and 75B breasts sizes was adopted to model the vertical dynamic movement of the breasts. A pneumatic system was designed with an auxiliary mechanical device that the manikin can move up and down in a continuous repeatable motion, which corresponds to the heel strike in a gait cycle. In pressure evaluation of bras, a changeable wired bra design that allows adjustment of tension or replacement of the bra components such as changing the shoulder straps, removing the underwire in a flexible manner was used. Significant pressure differences were found between various bra conditions, particularly at middle of underbreast underwire curve, shoulder and back of underband. Results indicated that high stress-strain behaviour of the shoulder strap, and bra band and flexible bra cup materials resulted in high bra-manikin pressure due to increase in the compression and tension forces. To enhance bra comfort, the elastic material properties of the shoulder strap and underband together with their corresponding lengths in pattern development should be well balanced for an optimum fit and pressure distribution. In breast displacement evaluation, most of the donned bra conditions can effectively reduce the vertical breast displacement especially for the upward motion as compared to braless condition. Length of shoulder strap and underband, choice of low stress-strain property of shoulder strap and underband material, flexible cup material and underwire insertion not only affected the bra-skin pressures, but also associated with the control of vertical breast motion. Subject-specific empirical model was formulated to predict the breast motion behaviour. Independent variables of breast size, underband length, cup material modulus, shoulder strap and underband material modulus, underwire and gait speed were regarded as important variables in the prediction of vertical breast displacement. The soft manikin showed a satisfactory result validated by a subject wear trial, thus providing a reliable and objective approach for future bra studies. To improve the support of breast, a new bra insert with aims of improving fit and control of breast displacement has been designed with reference to the natural curvature of the underbreast. It consists of an extended part from the curve to cover part of the breasts which helps to redistribute the weight of the breasts to the torso and therefore redistribute the impact during movement. Compared to conventional planar underwires, the newly designed bra insert exhibited a better performance in controlling breast motion. The insert design for ergonomic bras would provide a good reference to improve bra support, fit and comfort for women in daily activities.