- Well-fitted and supportive sports bras can reduce exercise-induced breast discomfort when women participate in physical activity.
- Although biomechanics research has provided information upon which sports bras have been designed, many studies have been limited by poor research designs and inadequate methodologies.
- Future breast biomechanics studies should use valid and reliable methods to understand the complex three-dimensional breast kinematics and kinetics, as well as the breast structure, of participants who represent all women globally.
- To improve poor bra fit, we must standardize commercial bra sizing internationally and base it on valid and reliable methods that can account for the combined breast and torso characteristics of women across the age, body mass index, race, and breast and torso size and shape spectrum.
Biomechanical research has consistently shown that breasts, which have no substantial anatomical support (1,2), move relative to the chest wall when women participate in physical activity (3–13). This breast motion is exacerbated during activities in which a woman's torso moves vertically, such as running and jumping (3–22). Unfortunately, excessive breast motion has been associated with exercise-induced breast pain, which can negatively affect the performance of skilled female athletes (15,23,24) and even prevent some women from participating in physical activity altogether (15,18,25–27). For this reason, wearing external breast support, such as a sports bra, is typically recommended for women when they exercise to reduce excessive breast motion and any associated breast discomfort or pain (11,18,20,21,26,28–32). Indeed, for female athletes, a well-fitted and supportive sports bra should be considered an essential piece of sporting equipment (20,31,33–36). Surprisingly, however, few sporting organizations, sports medicine associations, or public health education programs provide evidence-based guidelines on breast support for active women. Although most female athletes report wearing a sports bra when they exercise (15,33,34,37–39), a high percentage of both active women (44%–72%) and female athletes (44%) also report experiencing exercise-induced breast pain (3,17,23,24,34,35), as well as frictional injuries caused by their sports bras (40,41). These injuries and pain are despite the extensive biomechanical research that has been conducted over the past decade in an attempt to improve sports bra designs (10,11,19,25,42–51). More systematic research investigating breast biomechanics and better translation of research outcomes from these studies is, therefore, necessary to provide valid, reliable, and meaningful information upon which to improve sports bra designs for women who want to participate in physical activity.
Our primary aim in this article is to provide an overview of key studies examining the biomechanics of breast motion and to highlight how the results of these studies have been translated to design breast support for active women. We have highlighted limitations on current breast biomechanics research, as well as gaps in knowledge with respect to sports bras for women with unique breast support requirements. We have also posed key questions that need to be addressed in future research to develop a greater understanding of breast support for active women. The results of such future research, if conducted in a systematic manner, could ultimately enable women of all breast sizes, ages, and unique breast support needs to participate more comfortably in physical activity and sport without being limited by their breasts.
HOW HAS BIOMECHANICS RESEARCH INFLUENCED SPORTS BRA DESIGN?
The first bra designed specifically to support a woman's breasts during running is thought to have been developed in 1977 when a costume designer sewed two jock straps together for an avid runner to form the prototype “Jogbra” (52). There was an increasing demand for sport-specific bras in the 1970s after the United States introduced legislation (Title IX of the Educational Amendments of 1972; https://www.justice.gov/crt/overview-title-ix-education-amendments-1972-20-usc-1681-et-seq) that prohibited discrimination on the basis of sex in any educational program or activity that received federal funding, and this included sport (4). Sports medicine research investigating issues specific to female athletes began to emerge, which identified that breast pain during exercise could be problematic for women, particularly when women participated in sports that involved running (3,53,54). Biomechanists began to investigate the underlying mechanisms of this exercise-induced breast pain using high-speed cinematography to characterize the three-dimensional sinusoidal motion of women's breasts while they ran on treadmills and how this motion was influenced by varying levels of breast support (4,17,54,55).
Biomechanics of “Breast Bounce”: What Do We Know?
Since the initial research investigating breast motion (4,17,54,55), numerous biomechanical studies have confirmed that when women run on a treadmill without wearing external breast support (i.e., bare breasted), their breasts will move substantially (3–11,13,17,19–22,25,55–63). In the vertical direction, breasts will move, on average, 4.2–9.9 cm (3–11,13,17,19–22,25,55–63); however, values as high as 17 cm during jumping have been reported (14). Vertical breast displacement during running is closely linked to foot strike (8,19,20). That is, when a woman's foot strikes the ground while she runs, the vertical descent of her torso will abruptly decelerate. As a soft tissue structure, however, the woman's breasts will continue to move downward before also abruptly decelerating, but only after her torso has reached its lowest point and has begun to ascend (1,20). This time lag between when a woman's torso and breasts reach their lowest point can cause the breasts to “slap” down against the woman's torso (7–9,12,15,19,20). In fact, “breast slap” is thought to be a primary cause of exercise-induced breast pain during running (3,7–9,20,62), rather than breast displacement per se. In contrast, breast motion in the medial-lateral and anterior-posterior direction is linked to how a woman moves her upper limbs or rotates and laterally flexes her torso (5,6,11). It has been reported that breasts move on average 1.8–6.2 cm in the medial-lateral direction and 3.0–5.9 cm in the anterior-posterior direction (6–11,14). These breast displacement values, however, should be treated with caution due to limitations on breast biomechanics research, as discussed hereafter.
Irrespective of activity type, the total amount of breast movement during physical activity is a combination of how much the breasts are displaced and the number of times a woman's breasts “bounce” (15,20). The frequency and total number of breast bounces during running are governed by step rate because of the inherent link between breast bounce and foot strike, as described previously (8,12,19,20). Depending on how long a woman is active, the number of breast bounces she will accumulate during an activity can be extensive. For example, if a woman runs with a cadence of approximately 160 steps per minute, her breasts can bounce approximately 9600 times during 1 h of running (8,20). Women who run with a higher cadence and those who run for sustained periods, such as during ultramarathons, can experience many breast bounces and also have a heightened risk of incurring frictional injuries to their breasts and torso (40), as described elsewhere in this article.
Although a plethora of biomechanical studies have documented how women's breasts move during running, relatively fewer researchers have investigated the forces generated due to breast motion when women are active (12,20,64). The net forces associated with breast movement while a woman is active include the force of gravity acting on the breasts and the driving force of the torso, which are restrained by the stiffening and dampening forces associated with the anatomical restraints of the breasts and the external restraints of the bra (12,20,64). Because force is equal to mass multiplied by acceleration, the forces generated by the breasts during activity are greater in women with large breasts (greater breast mass (65)) relative to their counterparts with smaller breasts (11,12,20). The forces generated by breasts are also higher during activities in which torso and breast acceleration are higher, such as during horse riding compared with cycling or jumping compared with walking (5–7,9,10,14,17,19), or when limb cadence is faster (5–7,9,10,14,16,19,20). It is important to understand breast kinetics because the bra-breast forces generated during physical activity provide essential information upon which to design bras that can adequately and comfortably support the loads generated when women exercise (11,20). How breast motion can affect loading of the upper torso is described in detail elsewhere (1).
Biomechanics of Breast Support: What Does the Research Mean?
A plethora of biomechanical studies have documented the breast displacement that occurs while women exercise wearing varying levels of breast support (4–13,16,17,20–22,25,50,55,57–63,66–69). The studies have consistently shown that breast displacement decreases as the level of breast support increases (4–13,16,17,20–22,25,50,55,57–63,67–69). Furthermore, as breast displacement decreases, ratings of exercise-induced breast pain also tend to decrease (4–13,16,17,20–22,25,50,55,57–63,67–69).
With the translation of the results of this breast displacement research into practice, most sports bras traditionally have been designed to minimize the amount of breast displacement that occurs while women participate in physical activity. The two most common types of sports bras designed to limit breast displacement are: (i) crop tops; and (ii) encapsulation sports bras. Crop tops limit breast displacement by being made of strong elastic material, which compress the breasts as a single unit firmly against the chest wall. Encapsulation sports bras limit breast displacement by encasing each breast in a separate structured cup and supporting the breasts primarily via a band that encompasses the chest, with secondary support provided by independent straps (4,25,42). Because encapsulation sports bras have been found to be superior to crop tops in limiting vertical breast displacement (4,5,42,52,55), crop tops are typically recommended for women with smaller breasts, whereas women with larger breasts are usually encouraged to wear encapsulation bras (26,32).
Sports bra designers and manufacturers also have translated the results of breast biomechanics research by marketing and evaluating the “success” of their sports bras predominantly on the amount a bra could reduce vertical breast displacement. Marketing campaigns for these types of sports bras imply that the most effective sports bras are the ones that limit breast movement the most, with some sports bras marketed on their ability to minimize, if not completely eliminate, breast bounce (e.g., https://www.sportsbrasdirect.com.au/sports-bra-brand-focus-shock-absorber/). Such marketing campaigns, however, oversimplify how the results of biomechanics research should be translated because sports bras should not be designed to completely eliminate breast bounce. In fact, sports bras that reduce breast displacement the most also have been perceived to be the most uncomfortable to wear (4,25,49,55,62). Because breasts contain a high percentage of adipose tissue (70–72), there is a limit to the capacity or tolerance of breasts to be overly compressed or restricted before a sports bra becomes too uncomfortable to wear. Instead, bras that limit vertical breast displacement by approximately 60% relative to when a woman is not wearing a bra are sufficient to be deemed high-support sports bras (9,49,62).
More recently, “hybrid” sports bras, which integrate features of a traditional crop top and an encapsulation bra into one bra, have emerged. Hybrid sports bras have two separate cups that elevate and support each breast independently, covered by an external layer that compresses the breasts against the chest wall. Rather than just minimizing breast displacement, well-designed hybrid sports bras can reduce exercise-induced breast discomfort by minimizing “breast slap,” which is achieved by simultaneously elevating and compressing the breasts (25,57,73). Elevating the breasts can reduce tension and loading of the passive anatomical breast support structures, the overlying skin and Cooper's ligaments, by keeping these structures further from their end of range (25). The external layer then compresses the breasts against the chest to decrease the flexion torque generated by the breasts about the thoracic spine by decreasing the distance between the center of the breast mass and the thoracic spine (20,25,57). A hybrid sports bra is also consistent with the recommendation that women with large breasts (i.e., breast volume > 700 mL (65)) wear two bras (an encapsulation bra with a crop top worn over it) to achieve sufficient breast support (26,32).
What Features Should You Look for When Selecting a Sports Bra?
Irrespective of the type of bra, the level of breast support provided by a sports bra, and how comfortable a sports bra will be to wear, will vary depending upon its specific design features (4,18,49,55,62). Although no one sports bra will suit all women, factors that need to be considered when selecting sports bras are summarized in the Table. Importantly, the factors included in the Table highlight that the ability of a sports bra to limit breast displacement and, more importantly, breast slap should only be two of the many factors that need to be considered when choosing a sports bra. The importance of each factor will also vary with a woman's age, her breast size, and the type of physical activity in which she participates (26,32).
Although sports bra designs have advanced and diversified since the 1970s, 44%–72% of women (3,17,34,74) and 44% of elite female athletes (15) still report experiencing exercise-induced breast discomfort. Many women also experience cyclic breast pain, referred to as mastalgia, which can be exacerbated by breast movement during physical activity (15,23,24). Mastalgia has been reported to affect 51%–79% of women (34,75) and 63% of elite female athletes (15,23,24). Furthermore, women with large breasts commonly wear two bras during moderate- to high-impact sports and exercise to achieve sufficient breast support (26,39). The high occurrence of breast pain reported by women during sport and exercise, the inadequate level of breast support during exercise for women with large breasts, and the large number of sports bra features that women dislike (76) suggest that current sports bra designs are not sufficiently catering for the needs of all active women. Future developments in sports bra design, however, will be successful only if limitations on current breast biomechanics research that underpins sports bra design, and how the results of this research are translated into commercial products, are identified and rectified.
What Are the Limitations on Breast Biomechanics Research?
Unfortunately, many of the studies published to date that have investigated breast biomechanics are limited by poor research design and inadequate biomechanical methods used to quantify complex three-dimensional breast motion. Consequently, sports bras that have been designed based on this research have not catered for the individual needs of many women. Limitations on breast biomechanics research have been described in detail elsewhere (1,2). In brief, most studies have included only relatively young Caucasian women who have small- to medium-sized breasts and a body mass index (BMI) in the healthy weight range (3–10,12,13,17,20,21,25,55,57–59,61–63,67,77). These participants, however, do not represent the broad diversity of women globally. Future breast biomechanics studies should, therefore, include older women, women with higher BMI scores, and women from diverse racial groups, particularly because the breasts of women of different age and BMI (65,78), and from different racial backgrounds, have been shown to differ from each other (16,60,76,79). Breast motion has also primarily been measured for women who are walking and running on a level treadmill in a constrained laboratory environment (3–11,13,17,19–22,25,55–63,68,69,77). These activities do not represent the numerous sports and exercises women participate in, each of which is likely to have varying breast support requirements in different planes of motion (15,28). Breast motion also typically has been measured using only one marker, usually located on the nipple, often relative to another marker representing the torso or where the torso is treated as a single rigid body (3–11,13,17,19–22,25,55–63,68,69,77). The breasts, however, are complex, soft-tissue masses of varying densities that lie over deformable muscles (70,80–82) and are anchored to the chest wall by attachments with varying material properties (80–82). A single reference point on the nipple, irrespective of whether it is under or over a bra, is unlikely to accurately capture the complex three-dimensional breast motion (5,11,57,83). Furthermore, the torso is not a single-segment rigid body, and there are therefore likely to be errors in breast motion data due to inappropriate marker movement, particularly if the markers used to define the torso segment are placed on areas of high adipose tissue, such as the anterior abdominal wall (1). Consequently, torso and breast displacement data and their derivatives, such as velocity and acceleration, must be considered with caution (1).
Due to the limitations on current breast biomechanics research, further studies are required to develop more valid and reliable methods that accurately measure the complexities of three-dimensional torso and breast motion, including more representative cohorts of women performing a variety of body movements and sporting activities. This would provide robust evidence upon which to design future sports bras that can better support the breasts of women and allow them to exercise in comfort, regardless of their age, race, BMI, breast size, or preferred sport. However, irrespective of how well designed a sports bra is, if the bra does not fit a woman correctly, it will not adequately support her breasts (2,84,85). Correct fit is therefore essential for a sports bra to provide sufficient breast support and be comfortable to wear (2,26,32,86).
BRA FIT: WHY DO WOMEN GET IT SO WRONG?
Despite its importance in breast support, poor bra fit is unfortunately common, with approximately 85% of women reported to be wearing ill-fitting bras (2,87–89). This has been attributed to three primary factors: (i) a lack of knowledge among women regarding both the need for proper breast support during physical activity and how a bra should fit (2,29,90), (ii) poor standardization of bra sizing by bra manufacturers (2,86,91,92), and (iii) inadequate bra designs (84,85,92–94).
Despite the importance of proper breast support for active women, education pertaining to breast support and bra fit is rarely, if ever, included in the school curriculum (29), highlighted by the public health sector, provided to female athletes by sporting organizations (26), or included in sports medicine textbooks (18). This is particularly concerning given that educating adolescent girls about correct bra fit and breast support has been found to significantly improve girls' knowledge, as well as their breast support choices and bra fit behavior (90). Research and education about breast support and bra fit are also important to overcome myths that can deter women from wearing a sports bra when they exercise. For example, although a stated deterrent for sports bra use is that perceived tightness around the chest impedes sports performance, research has confirmed that a correctly fitted sports bra does not significantly affect maximal exercise performance or respiratory function during submaximal exercise (95).
The basis for confusion about bra sizing becomes clearly apparent when exploring the vast variety of ways bras are sized globally. For example, crop tops are usually sized using relatively vague descriptors (e.g., small, medium, and large), whereby the anthropometric measurement range underlying each size descriptor, if any, differs vastly among bra brands. In contrast, the size of an encapsulation bra is usually expressed as a combination of a number, which represents the bra band length, and a letter, which represents the cup size (25,47,86,92). Band sizes are usually based on measuring a woman's chest circumference directly under her breasts (i.e., the under-bust chest circumference) (25,47,86,92). In the United States and United Kingdom, band sizes are measured in inches and typically range from 28 to 56 (https://www.herroom.com/bra-size-conversion-chart,1355,30.html). This number, however, varies widely internationally because different countries adopt different units to calculate band size and express band sizes in different ways (e.g., dress sizes vs measurements), necessitating complex bra band size conversion charts (https://www.sizeguide.net/bra-sizes.html). Cup sizes usually range from A to P and are typically based on measuring a woman's chest circumference over the prominence of her breasts (i.e., over-bust chest circumference), relative to her under-bust chest circumference (25,47,86,92). There are, however, large inconsistencies in how bra cups are sized, thereby again requiring bra cup size conversion charts (https://www.herroom.com/bra-size-conversion-chart,1355,30.html). Furthermore, cup size is not homogeneous in different band sizes, such that a woman's bra cup size will be different in a different band size (91). More importantly, researchers have questioned whether simple chest circumference measurements can adequately represent the three-dimensional shape of female breasts or the different torso-breast dimensions of women (28,79,85,86,88,92,94,96). To compound problems associated with bra fit, the sizing of most bras is based on a prototype size, derived from directly measuring only one or two women who are arbitrarily deemed “fit models,” with sizes then heuristically scaled up or down based on prototype sizes (97).
Given that existing research has revealed that the negative health outcomes associated with poorly supported large breasts can be relieved by up to 85% by ensuring women wear a correctly fitted bra (87,98), it is imperative that strategies are developed to ensure women can select a bra that fits them correctly (2). First, to improve bra fit, commercial bra sizing should be standardized internationally and be based on valid and reliable methods that can account for the true anthropometric dimensions and characteristics of both the breast and the upper torso of women across the full spectrum of ages, BMIs, races, and breast and torso sizes and shapes. Second, for a bra to fit correctly, the cups must match the three-dimensional shape and volume of the breasts they are required to contain (2,47,79,85,94,96). Bra sizing could therefore also be improved by using evidence from three-dimensional scanning studies that have quantified both the volume and shape of female breasts (65,99,100), or from databases of whole-body scans that are currently publicly available around the world (e.g., Size UK; https://www.size.co.uk/). Finally, it is imperative that bra manufacturers produce products that adhere to any future international standardized bra sizing system so that women can more easily select sports bras that fit correctly.
WHO NEEDS SPECIALIZED BREAST SUPPORT?
The optimal level of breast support to minimize exercise-induced breast pain depends on age (15,28,84,101), breast size (10,12,14,20,28), and activity type (5,7,12,14,15,20,28). Differences in breast and torso shape can also make achieving sufficient breast support and correct bra fit more challenging for different cohorts of women, particularly when there is a dearth of research focusing on these women. Key questions that need to be addressed in future research to develop a greater understanding of breast support for these unique cohorts of women when they participate in sport and exercise are summarized hereafter.
Women with Large Breasts
Approximately 35% of women have either large (breast volume, 700–1200 mL) or hypertrophic (breast volume, >1200 mL) breasts (65). Women with large or hypertrophic breasts experience greater exercise-induced breast pain (3–11,13,17,19–22,25,55,58,60–63,68,69) and participate in less-vigorous–intensity physical activity compared with their counterparts with smaller breasts (27,34,102,103). Women with large and hypertrophic breasts also report increased pain and pressure generated at the bra strap–shoulder interface, which can cause deep furrows in the soft tissue where the bra strap lies on the shoulders (20,104,105). The downward pressure generated by bra straps can also result in paraesthesia and fatigue in the upper limbs, occasional complaints of puffy blue hands, and in more severe cases, ulnar nerve dysfunction (26,51,106). Women with large breasts also report: (i) more frictional skin injuries from their bras (40); (ii) an increased flexion torque on the thoracic spine (35,102,107–110); (iii) increased thoracic kyphosis (107,110–112); (iv) higher upper torso musculoskeletal pain scores (35,102,107–109,111), and (v) greater difficulty achieving correct bra fit (87). Breast size has even been shown to affect some temporal measures of respiration during rest and maximal effort exercise (95). In fact, women with large breasts often seek breast reduction surgery in an attempt to alleviate the issues associated with having large breasts (111,113).
Breast size and BMI have been found to be positively correlated (114–116), whereby overweight and obese women have breast volumes two to three times greater than women with a normal-range BMI (65). Because exercise-induced breast pain is often a barrier to physical activity in women with large breasts (20,27,110), this can perpetuate a reverberating cycle because reduced energy expenditure associated with decreased physical activity can contribute to weight gain and, in turn, increased breast mass (20) (Fig. 1). Although participating in physical activity is recommended for overweight and obese women to reduce their weight loss (35,117), not being able to find a comfortable bra to exercise in (27,35) and exercise-induced breast pain (27,33,35,107,110) have both been identified as barriers to physical activity in this cohort. Further research must, therefore, focus on developing sports bras that can adequately support the loads created by these large breast volumes (65).
Women Who Are Pregnant and Breast Feeding
During both pregnancy and breastfeeding, finding breast support that is effective and comfortable is challenging because of the changes to breast structure (118) and fluctuating breast mass (119,120). Women who are pregnant or breastfeeding are usually excluded from breast biomechanics studies (4–13,16,17,20–22,25,50,55,57–63,67–69). Furthermore, we could not find any published research that specifically investigated the breast biomechanics of women who were pregnant or breastfeeding and their breast support needs during physical activity. Further research, therefore, recommended to address gaps in our knowledge about the breast biomechanics and specific breast support needs of women who are pregnant or breastfeeding while they participate in physical activity to provide evidence for clinical guidelines on breast support for these women.
Women Who Are Older
The world's female population is aging, with the percentage of the world's population over the age of 60 yr expected to increase from 12% to 22% by 2050 (121). During and after menopause, the glandular tissue of the corpus mammae of the breast regresses and atrophies to approximately a third of its original volume, in a process called involution (118). Breast composition and density consequently change during this period, whereby the percentage of adipose tissue increases as the percentage of glandular tissue decreases (72,122). The skin overlying the breasts also becomes thinner as a woman ages, and the elasticity of the supporting connective tissue (within the overlying skin and fibrous tissue within the breast) decreases (101,123). These changes decrease the level of anatomical support provided by the overlying skin and fascial connections of the breast to the chest wall (1). The level of breast support provided externally by the bra, therefore, needs to increase in older women to compensate for their reduced anatomical support (28,101,124). The breasts of older women also commonly change their shape, becoming more ptotic (drooping) with increasing age (78,101,109,125). These changes make finding a comfortable, correctly fitted sports bra a challenge because the “fit model” used by bra manufacturers to size their bras is usually a woman who is younger than 35 yr (97,109,124,126). The difference in breast shape between older and younger women (78,101) is likely to make correct bra fit more difficult to achieve for older women relative to their younger counterparts.
Surprisingly, none of the published biomechanical studies that have investigated breast kinematics and breast support have included study participants with a mean age greater than 35 yr. Although there has been some research on the breast support preferences of older women, confirming that they are different from younger women (84,124,126), there is a paucity of scientific evidence upon which to design sports bras for older women (109). Further research is, therefore, required on the breast biomechanics of older women. Public health education for older women, bra manufacturers, and bra fitters is also required to ensure these sectors understand how breasts change as women age and how these changes affect breast support.
Women Living with Breast Cancer
Breast support is also an important issue for women living with breast cancer because of the changes to the breast and torso structure after breast cancer surgery, whether it be breast-conserving surgery, a mastectomy, or reconstructive surgery (30,127). Furthermore, the physical side effects of breast cancer surgery, such as skin and scar sensitivity, breast asymmetry, deformities of the chest wall, loss of the inframammary fold, and lymphoedema of the chest wall, breast, and upper limb, can make finding a comfortable and correctly fitted bra challenging (30,127). External breast prostheses can also cause problems, such as increased pressure at the bra strap–shoulder interface (128), and are commonly perceived to be too heavy and feel asymmetrical compared with a woman's intact breast (128–130). Further research is therefore required to develop evidence-based strategies to improve the breast support options and bra fit of women living with breast cancer.
Difficulty finding a comfortable bra also has been found to be the third highest barrier to physical activity for women living with breast cancer (31,127). After surgery, however, women currently receive limited and inconsistent education or treatment as part of their standard postoperative care to manage their unique breast support issues, particularly breast support during physical activity. Considering the well-established health benefits of regularly participating in physical activity, and the importance of physical activity to limiting the risk of breast cancer reoccurrence (131), formal education about the importance of adequate breast support should be mandatory for all women after breast cancer surgery.
Breast support is important for adolescents because of self-consciousness related to body image, particularly embarrassment related to excessive breast movement during exercise, which is a barrier to physical activity in this younger cohort (27,29,33,90). Research suggests, however, that knowledge about breast support and the bra-wearing behavior of adolescent girls is poor (29,90). Education on breast support and bra fit during adolescence should consequently be a priority for high school physical and health education programs. The sensitivity over body image during this time (33,132) also suggests that sporting uniforms should ideally not accent the breasts of adolescent girls, and that research on how uniform design can be enhanced to foster adolescent girls participating in physical activity is also warranted.
In contrast to popular belief, not all female athletes have small breasts (15,23,90). In a recent study of 436 elite female athletes, 27% were classified as having “medium-to-hypertrophic breasts” (28). Furthermore, 44% of the female athletes reported they experienced exercise-induced breast pain, and 32% of these participants perceived this breast pain as negatively affecting their sporting performance (15). Sports medicine associations and sporting organizations should, therefore, be proactive in educating athletes and coaching staff about breast support and bra fit to decrease the potential negative effects of exercise-induced breast pain and mastalgia on athletic performance.
Further research is also required to explore breast biomechanics during the variety of sports that women participate in to provide evidence upon which to improve sports bra designs for athletes across the wide spectrum of sports. Female athletes, particularly older athletes, those with larger breasts, and those in endurance sports, also often experience frictional injuries (lacerations or chafing) to the skin under their sports bra or uniform (40,41). The increased incidence of frictional breast injuries with increasing age and breast size is most likely due to changes to the skin with age (101), as well as increased breast motion associated with larger breasts (10,20). Further research investigating strategies to prevent frictional breast injuries, particularly for older athletes and those with larger breasts, is strongly recommended.
FUTURE PERSPECTIVES: WHERE TO NEXT?
Can We Rethink Sports Bra Designs?
Although there have been substantial developments in materials and manufacturing processes since the Jogbra, the notion that sports bras should be designed primarily to restrict breast motion (133,134) has not changed substantially since the 1970s. This is despite evidence that bras that reduce breast displacement the most are usually perceived to be the most uncomfortable to wear (4,25,49,55,62). Furthermore, the level of breast support required during physical activity, especially within team sports, commonly fluctuates depending on the type of physical activity being performed. Sports bras that can respond to the individual requirements of women by sensing changes in the amplitude and frequency of their breast movement and adjusting the level of support to match this motion have the potential to maximize both breast support and bra comfort. Indeed, electromaterials have been shown to successfully sense changes in breast motion while women walked and ran on a treadmill, whereas electrothermally driven artificial muscles have been shown to tighten a bra to provide more perceived breast support (77,134).
Although these innovative technologies have the potential to revolutionize sports bras by providing individualized breast support for active women, numerous challenges with such technology currently exist, such as how to integrate any such technology into a garment that is both comfortable to wear and robust enough to be washed (77). As well as improving the validity and reliability of biomechanical studies, future research must also explore ways to overcome these challenges to ensure the next-generation bras provide the necessary range of breast support for women participating in a variety of physical activities. Irrespective of the technology used in future bra designs, a better representation of women likely to wear sports bras must be engaged in the research process to ensure any final bra prototype meets its objective goals of reducing breast motion, as well as the subjective criteria such as comfort, fit, and aesthetics (77).
Breast Biomechanics Research: Where to Next?
As stated previously, many of the published breast biomechanics studies are limited by poor research designs and inadequate biomechanical methods such that many commercially available sports bras based on the results of such studies do not cater for the individual needs of many women. Apart from improved research designs, comprehensive research extending beyond just breast kinematics is required to provide the necessary evidence upon which to improve the design of sports bras. Contributions to designing a better sports bra could arise from investments in research pertaining to breast structure and anatomy (70,80–82), three-dimensional scanning of breast and torso size and shape (43,85,94,99,100,135), clinical measurements of the upper torso musculoskeletal system (58,102,107,110), static and dynamic loading at the bra-torso and bra-shoulder interface (51,57,128), the effect of breast support on muscle activity (59,108,136), three-dimensional modeling of the breast (137–139), breast skin tissue mechanics (101), and materials engineering (44,48,50); these could all contribute to designing better sports bras (Fig. 2). It is also imperative that biomechanists collaborate with researchers from diverse disciplines (e.g., industrial design, human factors, apparel design, and marketing) so that research teams with the most appropriate expertise are formed to meet the complex challenges associated with developing better sports bras. If conducted in a systematic and robust manner, such future comprehensive multidisciplinary research could provide valid and reliable evidence upon which to develop breast support solutions, and to ensure these solutions are translated in a timely manner into commercially viable products. This will ultimately enable women of all breast sizes, ages, and unique breast support needs to participate comfortably in physical activity and sport, unimpeded by their breasts.
We thank Jessica Laing (www.seeillustrationsfordetails.com.au) for assistance with the illustrations.
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