Abstract:

Objective Anti-shock performance of sports bras is closely related to the tensile properties of fabrics adopted to produce the sports bras, but seldom research was published on the qualitative and quantitative relationship between the two aspects. The aim of this study is to explore the quantitative relationship between the tensile properties of cup fabrics and the shock-absorbing performance of sports bras, and to provide data support for the optimization design of sports bras in the future. The study also aims to investigate the fabric stretching condition of sports bra during exercise.

Method Three coordinates of seven markers representing the trunk and breast movement were recorded with no bra and with six sports bras used. A dynamic mannequin with 75C-cup breasts was adopted to simulate the vertical breast movement at the running speed of 10 km/h. Six sports bras were produced with exactly the same structure, and the same materials except for the cup materials which were with different elasticity modulus in vertical direction. The quantitative relationship between elasticity modulus of cup materials and vertical breast displacement relative to trunk was fitted by ten curve-fit models. The static and dynamic stretch of cup materials were measured and calculated.

Results The mean maximum dynamic stretch of the six cup fabrics was (53.44±2.75) mm (rangeing from 50.63-58.55 mm). The mean maximum dynamic elongation of the six cup materials was 30.02% (ranging from 19.52% to 42.80%), implying that it is reasonable to select the elasticity modulus of 30% elongation as the index of cup fabrics. The vertical breast displacement under the no-bra condition was 21.84 mm, and the vertical breast displacement under the six bra conditions ranges from 9.69 mm to 19.76 mm. Pearson test result shows significant negative correlation (r=-0.886, P=0.019<0.05) between the elasticity modulus of cup materials and vertical breast displacement relative to trunk. Using vertical breast displacement under no-bra condition as the reference, less vertical breast displacement represents better shock absorption performance of a sports bra. The findings indicate that greater elastic modulus of cup fabrics induces better shock absorption performance of the bra, which may be resulted from greater stiffness of bra-breast unity relating to greater pressure at the interface of cup and breast exerted by cup fabrics. It was noted that the negative correlation between elastic modulus of cup fabrics and vertical breast displacement was nonlinear, and the vertical breast displacement decreased less as the elasticity modulus of cup materials increases. Eight of the ten curve fit models were screened by the significance of regression equations (P<0.05). The fitting degree (R²=0.891) of power function model was higher than that of other seven curve fit models, suggesting that power function can be adopted to predict the shock absorption performance of sports bras through the elasticity of cup materials. The quantitative relationship between the elasticity modulus of cup materials and vertical breast displacement can be expressed by the fitting equation lnB=-0.248lnE+ln64.289, where E represents the elasticity property modulus of cup fabrics and B represents vertical breast displacement of sports bra. The findings of this study also implied that it is feasible to employ the dynamic mannequin to evaluate performance and factors of the sports bras.

Conclusion The research showed that that 30% is a reasonable elongation to calculate the cup elasticity modulus when exploring the relationship between cup fabric and the performance of sports bra for women with 75C breasts when running at 10 km/h. The support performance of sports bras increases significantly as the elasticity modulus of cup fabrics increases. Power function can be adopted to predict the support performance of sports bras through cup elasticity modulus. For future research, the impacting mechanism of cup elastic properties on breast movement reduction should be explored by measuring the pressure exerted on the cup-breast interface and the stiffness of breast-cup unity.

Key words: sports bra elasticity modulus of fabric, shock absorption function, vertical breast displacement, curve fit, dynamic mannequin