The first thing to know about sports and breasts is this: women have always participated in athletics, bra or no bra. In ancient Rome, women bound their breasts with cloth and leather. Pottery and mosaics from the fourth and fifth centuries show female athletes wearing bikini-like uniforms.

In the Victorian era, women turned to corsets to keep their breasts from moving too much. Those competing at Wimbledon in 1887 returned to their dressing rooms in between matches to "unhitch their bloody corsets," having been "repeatedly stabbed by the metal and whale bone stays of the cumbersome garments" as they played.

By 1911, women got a "sports corset" with flexible material, and thanks to the 1914 tango craze, someone even invented a dancing corset. But it wasn't until the 1920s that bras started to replace corsets in the United States, and while brassieres designed for athletic purposes were patented as early as 1906, they simply never caught on.

Finally, in 1977 — the same year Victoria's Secret was founded — the sports bra as we know it was invented by Lisa Lindahl and Polly Smith, with the help of designer and runner Hinda Miller. That first sports bra was simply two jockstraps sewn together. It wasn't just that jockstraps were the right size, they were also the right idea. "We said, what we really need to do is what men have been doing: pull everything close to the body," Miller later told researchers. They called this new bra the Jockbra, but quickly changed it to Jogbra after store owners in South Carolina deemed the name offensive.

During its first year on the market, Jogbra moved 25,000 units. Two decades later, in 1998, the sports bra industry sold $412 million worth of product. A 2002 study estimated that sports bras accounted for about 6 percent of the then-$4.5 billion bra market. Today, the bra market is worth about $15 billion. Factor in that female participation in sports is increasing every year and athleisure appears to be here to stay, and it's no wonder that from Lululemon to Under Armour to Victoria's Secret, brands are turning their attention to sports bras.

But researchers are still a long way from understanding exactly how breasts move during exercise. Standing in the way of designing the best sports bra possible is millennia of stigma, powerful marketing forces, and good old-fashioned physics.

Breasts have no muscle. They sit on top of the pectoral muscles, but breasts themselves are all fat and glands and connective tissue. They're held to the chest by something called Cooper's ligaments, though those ligaments aren't designed to reduce movement. As one study puts it, "the skin appears to provide most of the support for the breast in regards to limiting breast movement."

That is to say that there is nothing biological working to stop breasts from moving. Without any such built-in support, as any person with breasts can attest, they bounce up and down freely, which can cause a fair bit of discomfort. When surveyed, between 40 and 60 percent of women report breast pain associated with physical activity. That pain makes women less likely to exercise, and among those who do, hurts their performance.

Understanding the biomechanics of bouncing is key to understanding how to make it stop, but it's a field that's only recently gained traction. And since breast size, placement, and density are different for every woman, researchers need to look at a large sample to get a good idea of what's going on.

Understanding the biomechanics of bouncing is key to understanding how to make it stop, but it's a field that's only recently gained traction.

Even two people with the same sized breasts might have different breast composition; put them in the same bra, and one might be in heaven while the other can barely breathe. "There are so many factors going on, it's hard to pin down that it's the bra," says Jenny White, a researcher at the University of Portsmouth who studies breast motion.

White's research aims to better understand how breasts move, and what that means for the people who have them. When volunteers come into her lab, she has them do a variety of physical activities in a variety of bras (and without one), and asks them to report how each activity and fit feels. She also uses a sophisticated motion capture system, placing reflective markers on the bra.

Recruiting for this kind of study can be hard, White says, but she came up with a clever strategy. In 2013, her team targeted female runners in the London Marathon: "At registration, we tried to accost as many of them as possible. We got about 1,300 people and we were able to understand that population."

It's one thing to be able to see a woman run in a bra in a lab. It's another to see what they experience after 26.2 miles. Over the course of a marathon, White says, "you might start seeing changes in the patterns of their running. You're probably going to see a decrease in stride levels. You're just not performing as well as you could."

On the other side of the world, at the University of Wollongong in Australia, Julie Steele does similar research. Women who sign up for Steele's studies come in and are all given the same standard issue, commercially-available bra. This lets the team compare how women fit themselves, how they're fitted by experts, and how they fill out and move in the control bra.

They then go through a series of tests to figure out the mechanics. "We use 3D scanning, ultrasounds, and devices that measure the skin to really better understand the structure of the breasts of these women," says Steele. "We really need to better understand how that goes together to make the breasts move."

Both Steele and White say there's a constant battle going on between controlling the bounce and making bras comfortable. You could squash the breasts tightly against the body, but that makes it hard to breathe. The most common complaint, in the long list of ways in which sports bras are painful, is that the straps are too tight, sometimes even causing them to break.

It's worth noting that wearing the wrong sports bra isn't just a matter of discomfort or annoyance. Studies have shown that breast discomfort is a leading reason women stop participating in sports. And in extreme cases, an ill-fitting bra can actually do nerve damage. Bra straps generally cross over the brachial plexus, the nerve bundle that sends impulses to and from the arm. Women who wear bras with too-tight straps can damage that bundle, causing pain and numbness.

Another thing Steele and White worry about is that women aren't wearing the right sized bra. A full 75 percent of the marathon runners White talked to had some kind of bra problem during training. "I think we need to scrap the whole bra system and start again from a sizing system," Steele says. Bra sizing is confusing, imprecise, and variable. This isn't just a sports bra problem, either; some surveys say that literally 100 percent of women are wearing the wrong sized bra.

A full 75 percent of the marathon runners White talked to had some kind of bra problem during training.

White says that the methods she, Steele, and their peers use to study breast movement might soon change dramatically. "We're at this crossover period," she says. White thinks that in the near future, they'll be using something called inertial sensors — tiny sensors that can be placed directly on the breast itself to gather GPS and acceleration data.

There are a few benefits to this new method. First, the sensors that attach to the breast directly rather than to the sports bra can tell researchers much more information about what the breast is doing underneath the bra. "So it means we completely get rid of any discrepancy between what the breast is doing and what the bra is doing," she says. In other words, if the bra is too big, or has padding or anything else that might make it move differently from how the breast itself is moving, the researchers will be able to detect that.

Second, these sensors don't require the camera setup that White's markers do, which means researchers could use them out in the field and see how breasts move in their natural environments, like during a soccer game or in a road race.

The sensor technology isn't quite there yet, but White says that it's coming: "It's been a slow development, they haven't been small enough to place on the breast. But they're getting that small, so we've got a provisional system."

Today, there are a lot more choices than the original Jogbra jock strap design. In fact, as anybody who has gone shopping for a sports bra recently can attest, there is an overwhelming number of choices, from strappy yoga designs to padded cups to the classic racerback. But the choices women face come down to two main categories: compression bras and encapsulation bras.

"Once you go above a certain size, you start coming out everywhere anyway."

Compression bras are the bras most people associate with sports bras — a single panel of fabric that hugs the breasts into the chest. The idea here is that if you can compress the breasts against the body, pulling them so they're closer to your center of gravity, they'll bounce less. Which is true, as long as the breasts in question aren't too large.

Encapsulation bras treat each breast individually, more like a regular bra. While compression bras work perfectly well for women who fall into the A- and B-cup range, larger breasted women need more support. Some studies suggest that encapsulation bras can provide that, but not everyone is in agreement. In 2009, White found that for D-cup women, the difference in breast displacement between a compression bra and an encapsulation bra was insignificant.

"Once you go above a certain size, you start coming out everywhere anyway," White explains. She also notes that compression bras are far more common in the United States than elsewhere in the world. For very large breasted women, some bras combine the two strategies, using individual cups for each breast with an outer compression layer on top.

In October of last year, Nike announced a new line of athletic gear for women, including sports bras, that it hoped would bring in $2 billion annually by 2017. This year, Under Armour announced its plans to reach $7.5 billion in sales, and as part of that growth, executives have pointed to its growing sports bra line.

It's not just athletic brands getting in on the action either; designers of all stripes are dipping their toes into the athletic market. Designer Mara Hoffman just released an activewear line that includes colorful sports bras. Rebecca Minkoff and Tory Burch recently did the same. There's even a startup trying to disrupt the sports bra industry.

While there are suddenly a ton of options out there for women, not all of them are good. "There is no piece of clothing that is more difficult to design well than a sports bra," says LaJean Lawson, a breast researcher and consultant for Champion Athletics. "There are so many different parameters. It's the most hooked into cultural stereotypes. You have to think about sweat, support, chafing, straps, slippage, and then looking cute. That's a really long list of conflicting design requirements."

Lawson has been studying breasts, their movement, and the bras that contain them for Champion since 1984, when she tested the original Jogbra. In 1987, she evaluated the seven sports bras Champion had on offer using a 16mm film camera. Today, she employs the same methods that White's lab does, using complex camera tracking to test hundreds of bras both from Champion and other companies. "I just ordered $1,000 worth of Victoria's Secret sports bras to test in the lab," Lawson says, "and they called me and asked, ‘Who are you, and why are you buying all these bras?'"

White's team works directly with brands who want to evaluate their bras using her methods. She runs breast science workshops a few times a year, where representatives get an introductory crash course and learn ways bras can be designed to help reduce pain. From there, White offers her lab's services to companies who want to come in and test their designs.

"There is no piece of clothing that is more difficult to design well than a sports bra. It's the most hooked into cultural stereotypes."

One of the brands that has taken White up on the offer is Shock Absorber, a UK sports bra company that prides itself on its scientifically-supported designs. "Since this original research was carried out, Shock Absorber has tested all new styles at the University of Portsmouth to measure their reduction in breast movement," its site states.

White wouldn't share the names of other brands she's worked with, but Kelly Cortina, vice president of women's apparel at Under Armour, disclosed that her team has used the Portsmouth lab. There, Cortina says, "we tested on women of all different sizes to ensure that the bra is minimizing breast movement and managing moisture efficiently." White's lab offers everything from a basic bra test to a "gold-level" setup where the company gets heavily involved in the fundamental research the team is doing.

In her ideal world, White would work with brands from the very beginning of their design phase, so they can test out many iterations of their styles. But that's not how it usually happens: "Unfortunately many companies have gone through the whole process of design and they just want to know how good it is."

Lawson, on the other hand, gets to work on Champion's designs from the start. Along with a team of engineers, Lawson advises on seam placement, strap design, how to change contours, which parts will rub, and more.

White and Lawson keep a close eye on the trends in sports bras, and they have both seen a recent rise in bras with padding. "Last spring, when I did my last project, I had 12 bras to test," Lawson says. "Four were Champion, eight were competitors, and 10 out of those 12 had some kind of padding in them." White also saw more bras featuring lots of straps, and ones that look more like everyday bras: "I've noticed more sports bra that we're testing having underwire."

Here is where those athleisure offerings from brands like Mara Hoffman and Tory Burch are having an impact. "It's had a noticeable influence on what women want in their sports bra," Lawson says. "There have never been more products out on the market from non-athletic brands that don't have the structure and the design to meet women's needs when she's out kicking it hard on the road." Lawson adds that when she tests those bras on women in the lab, their flaws quickly become apparent. "When I can't get a woman to take an $80 sports bra home for free, I mean, that's a bad sign."

But this is the really tricky part: how good a sports bra is depends on what you're measuring. For White, the quality of a bra has everything to do with the comfort of the user wearing it. But for brands, that's not the only consideration.

Sports bras aren't just a piece of sports equipment. They're not like a bat or a baseball mitt or shin guards — designed, for the most part, for maximum functionality. They're cultural objects, they're fashion objects, and as such they're laden with all kinds of baggage about how a woman is supposed to look. "There's so much more to a sports bra than just a bra," says Jaime Schultz, a sociologist who studies women and sports.

Just look at the way sports bras are advertised. The very first ad for the Jogbra boasted that its "unique design holds breasts close to the body." Twenty years later, the company changed its tune. Suddenly, holding breasts close to the body, literally the entire purpose of the Jogbra, was a no-no. "Only abs should be flat," a new ad read in 1996. "Now, a sports bra that respects and defines your natural shape."

Today, Victoria's Secret is continuing the war against compressed breasts. They call this "the uniboob." Victoria's Secret chief executive officer Sharen Jester Turney announced last year that the war against the uniboob was in full force: "We wanted to solve the uniboob problem, where your sports bra makes you look straight across — no one likes that. This bra is just as much about performance and function as the look."

"One of my testers is an aspiring Olympic marathoner, she's a 32C and she's like, ‘I don't want to be flat.'"

Well guess what, sometimes the uniboob is in fact the best way to reduce breast motion and pain. But women are constantly being told that even their sports bra should be sexy. Styles with spaghetti straps and low V's and padded cups win out over wide straps and good support. "Women feel like they have to present themselves in the best possible breasted way that will appeal sexually," says Schultz.

Under Armour's Cortina echoed some of those sentiments in an email. "Women want to feel good and look good," she wrote. "Gone are the days of sacrificing style for fit or comfort. She expects and DESERVES a bra (no matter the cup size) to fit, perform, and be on trend. Many bras offer one but not the others. She wants it all and she can have it all!"

Lawson says that she hears from lots of women that they want padding, and while she herself is not a proponent of enhanced sports bras, she's also quick to say she doesn't want to dismiss other women's desires: "One of my testers is an aspiring Olympic marathoner, she's a 32C and she's like, ‘I don't want to be flat.' That shocked me, but that's one of those things that has turned my ideas on their ear in the last few years."

This is a perfect example of the "be everything at once" dilemma women face. A bra can't just be a good bra, it also has to be fashionable and womanly. It has to hold the girls nicely, without diminishing their size and shape. And when forced to chose between those two things, bra manufacturers almost invariably chose look over function.

When asked about the future of sports bras, Lawson talked more about materials than overall design. She expects we'll see materials "that can respond to breast impact so the control is local rather than being on the shoulder, materials that are better at responding to body temperatures and heat rates." The compression and encapsulation styles, she says, are serviceable enough. While they could certainly use improvements in form, the foundational system of sports bras probably won't change much any time soon.

And therein lies the problem. Lawson or White or any bra designer could, tomorrow, invent the world's best sports bra. Something comfortable and supportive and soft and easy to put on and take off. Something that wicks away sweat while providing coverage. Something that doesn't pinch the shoulders or squeeze the rib cage. But if that sports bra isn't cute, it wouldn't matter. "I think the biggest problem is that a lot of it isn't based on science," says Steele. "It's based on fashion and look. And that's what sells."

Editor: Julia Rubin

Photo illustrations by Brittany Holloway-Brown