Q23 - Mechanical Change in Sports Bras Induced by Simulated Application and Removal

Saturday, October 11, 2025

10:00 AM - 11:00 AM PDT

Location: Exhibit Hall F, G & H

Presenting Author(s)

Julia Sides

Student
University of Rochester
South Burlington, Vermont, United States

Primary Investigator(s)

Mark R. Buckley

Primary Investigator
University of Rochester
Rochester, United States

Co-Author(s)

TS

Tasneem Sabir

Senior Lecturer
Manchester Metropolitan University, United States
TA

Thomas Allen, FIMechE

Reader
Manchester Metropolitan University
Manchester, England, United Kingdom
RG

Rebecca Grant

Senior Lecturer
Loughborough University
Leicestershire, England, United Kingdom

Last Author(s)

KR

Katherine Rizzone

Associate Professor
University of Rochester Medical Center, United States

Introduction: : Sports bras are essential equipment for girls and women to participate in sport and activity. Reduced breast support can increase trunk range-of-motion and lower extremity injury risk [1]. A supportive sports bra may mitigate these risks. Sports bras vary in their fabric compositions and construction; however, three key components are common in all bras, including the band strap, shoulder straps, and cup support. Most sports bras contain spandex, an elastomer which can stretch to exceptional length and recover to its original shape [2]. These components provide support and dampen breast motion, but there is currently no specific understanding of how these components fatigue over time and there are no recommendations on when sports bras should be replaced. Our objective was to develop a protocol to examine and analyze how the mechanical properties of sports bras change with use. We aimed to measure changes in the stiffness and length of the bra band strap under a cyclic loading protocol that simulates repeated application and removal of the bra – the phases where the band strap undergoes maximum deformation. Additionally, we aimed to observe how the bra band material recovers over time following cyclic loading. We hypothesized that cyclic loading would lead to permanent bra deformation and reduced bra stiffness, with these mechanical changes becoming more pronounced as the number of loading cycles increases. We further hypothesized that the length of the sports bra band would recover only partially with rest.

Materials and

Methods: : A load controlled cyclic loading protocol using a uniaxial tensile test system was developed to assess how the mechanical properties of the bra band are affected by repeated application and removal (300x), and whether these properties recover with rest (Fig. 1). To start, 30 mm testing segments were marked 30 mm apart from each other down the length of the bra band (Fig. 2A, 2B). Testing was performed on the intact bra band. After preloading, the protocol began with a diagnostic test (DT) where the segment was stretched to 10 N, the force required for accurate stiffness and length calculations, before returning to its resting position. DTs in the protocol were used to determine segment stiffness (N/mm), length (mm), and energy dissipated (N mm) (Fig. 2C, 2D, 2E) using a custom MATLAB code. After the initial DT, the segment underwent a single loading cycle to 50 N, the assumed force the bra band undergoes during application, followed by DT #2, a 10-minute rest, and DT #3. Next, 99 loading cycles were applied to 50 N, followed by DT #4, another 10-minute rest, DT #5, 200 additional loading cycles to 50 N, DT #6, another 10-minute rest, and, finally, DT #7 (Fig. 1).

Results, Conclusions, and Discussions:: Results and

Discussion: We observed that with cyclic loading, the sports bra band stiffness and segment length were most affected by the initial stretch to 50 N of force. However, these properties gradually plateaued with additional loading (Fig. 2C, 2D). Our observation that the initial loading event caused the greatest permanent deformation is consistent with a known stress softening phenomenon, the ‘Mullins Effect’, where rubber-like materials exhibit an appreciable change in their mechanical properties resulting from the first extension [3]. The bra tested featured a racer back design, a continuous band without clasps, and two different textures, flat and ribbed (Fig. 2A, 2B). It was found that the mechanical properties of the bra band varied along the band. Segment 1, located on a ribbed section of the band, showed the highest stiffness and shortest length throughout the protocol, whereas segment 3, located on a flat segment of the band, maintained the lowest stiffness and longest length with cyclic loading. It was also found that a 10-minute rest following cyclic loading resulted in partial recovery of segment stiffness and length. The energy dissipated with each DT followed a similar trend to the segment length (Fig. 2E). Similar trends were observed with a strain control protocol and with different bra brands (data not shown).

Conclusion: Our cyclic loading protocol revealed how sports bra bands are fatigued with repeated application and removal. The greatest permanent deformation and loss of stiffness occur during the first extension, and these properties plateau with further load application. Only partial recovery is observed after a 10-minute rest. This study serves as a first step towards establishing informed guidelines on recommendations for sports bra use and replacement for girls and women.

Acknowledgements and/or References (Optional): : [1] Fong et al., 2022; [2] Singha et al., 2012; [3] Diani et al., 2008