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Sports Bras Part One: Biology and Biomechanics

In News

I have been thinking a lot about sports bras lately, and that inspired me to write a post. However, when I started writing, I realized there was a LOT of information and so we’re breaking this up into a series!

So stick around, we’re going to take a deep dive into learning more about how our bodies work today!

A quick word about the stats and facts I quote here. Many of them come from the fantastic work of Dr. Deirdre McGhee, who specializes in breast health and biomechanics at the University of Wollongong. She’s one of the only researchers in the world focusing on this as a full time research subject. She’s amazing.

Breast Biology

If you’re anything like me, you were never taught in health class about why we wear bras and how they fit. Which is crazy, because having a bra that fits you and supports you makes a huge difference to a developing teen, particularly when it comes to sports and staying active. Don’t feel bad, though - major sport organizations don’t have that information for their athletes, either, even though 44% of female athletes report breast pain during exercise. 

Our breasts are lumps of tissue that stick out of our chest. They are for feeding babies, primarily, and letting the world know our body is able to produce babies because TADA! I grew these lumps!

Inside of them, you’ll find ligaments (connective tissue), glands (that’s what makes the milk) and adipose tissue, which is a fancy way of saying fat. Unlike other mammals, whose breasts basically disappear when they aren’t actually producing milk, we humans carry our around from puberty until, well, you can tuck them into your panties before crawling in your coffin and waving goodbye to the world. Many of us often have cysts too - little pockets of fluid that aren't cancerous but make life more, shall we say, interesting. You could also have inserts from breast enhancement or reconstruction surgery.

Scientists aren’t really sure why we humans have these permanent fat lumps, but there is speculation that it’s a secondary sex characteristic we developed once we started walking and it became harder for men to see our sex organs and figure out if they wanted to jump us or not. (Don’t even get me started on all the ways the patriarchy tries to use evolutionary biology to enforce inequality. That’s a novella, not a blog post.)

But back to the boobies! How much of each type of tissue you have in your breasts depends on you, your age, your health, and where you are in the progression from menarche (puberty) to post-menopause. Generally speaking, once you pass through menopause, your glandular tissue decreases. Your adipose tissue can increase or decrease, based on your body and your activity levels. 

But why is all of this important to know?

Because our breasts don’t have muscles in them. All the support in them comes from the tissues inside, a few ligaments (connective tissue), and your skin. That’s it. That’s why most of us wear bras to provide us with support, so we can do more than lounge around naked on a chaise lounge and have our portraits painted. 

By Titian - bQGS8pnP5vr2Jg at Google Cultural Institute, zoom level maximum, Public Domain,
Venus of Urbino By Titian


What happens to our breasts when we move, then? Well, it’s complicated. And like many complicated things that happen to bodies with breasts, it hasn’t been studied by science in any rigorous way that actually matters to the entire population of people who have breasts. 

One of the reasons is that science is done at universities, where researchers use the students as an easy-to-reach pool of potential candidates. The result is that most research is done on white women under the age of 35 with a BMI in a healthy zone. Bra companies use that data to make their bras and sports bras - or they do their own studies, based on their target market (fit young people.) But I digress.

Here are the basics. When you do activities that cause your body to move up and down (anything from walking to jumping) your breasts also move up and down, but not at the same time. There’s a lag. The amount of the lag and the force at which your breasts come down goes straight back to basic physics. 

force equals mass times acceleration 

The bigger your breasts and the faster you’re moving, the greater the force they (and you) feel. That’s why activities where you would move faster or jump a lot require more support in your bra to counteract that force. 

What about when we’re moving from side to side? Dancing? Cross fit? Cleaning the house? Well, that causes side to side movement as well as vertical movement and lateral movement. Our breasts basically make figure eights when allowed to flop free. Who knew?  I’ll discuss this more when I’m looking at sports bra design.

woman in background with arms crossed, watching a young woman figure skate
I feel you, woman in the back.

Physical Discomfort versus Social Discomfort

Because we weren’t taught that our breasts don’t have muscles or support- and how they move, unless encased in concrete, is entirely natural - we feel a social awkwardness when our breasts bounce. Are people watching me? What are they thinking? This is so embarrassing. How many of us just quit the exercise and activities we love because we didn’t want to run up and down the basketball court while all the world watched our boobs bounce higher than the basketball? That's the social discomfort.

If the amount of force in that bounce (the scientific term for this is is the breast slap, which makes me wince and giggle at the same time) moves your breast enough that it strains your connective tissue, stretches your skin, causes too much friction, or squishes you too much, it hurts. 

That’s in addition to cyclic mastalgia. What’s that? Oh, something else we weren’t taught about in health class. If your body has menstrual cycles, you can have breast pain and swelling at different times of your cycle. That could make certain bras more painful to wear.

As an aside, it’s a great idea to track your cycle and how you feel every day for at least a full cycle, which will help you notice these things. Some women go up more than a cup size! Knowing this can help with picking the right bra to wear, and knowing when you should go bra shopping. 

Your sports bra needs to address these two things - your physical discomfort and your social discomfort - without making either of those problems worse. That is, you don’t want to be so squished that you’re more uncomfortable and it affects your ability to exercise. You also don’t want to wear a bra that makes you feel even more socially awkward. The ideal bra will reduce the movement so that you feel as little physical and social discomfort as possible.

It's more helpful to think about finding a bra for you that minimizes your social and physical discomfort than it is to search for a bra that eliminates bounce. The larger your breasts are, the less likely it is you will be able to eliminate bounce entirely and still exercise. Rather, pay attention and ask, am I in pain? Am I comfortable?

Let’s recap: 

  • Breasts are lumps of fat, glands, and connective tissue on your chest
  • They change with your health, age, and cycle
  • Studies on how they move when we move suck, because patriarchy, racism, ageism, and poorly funded researchers
  • When we aren’t supported, when can feel pain and we can feel embarrassed, both of which suck

In my next post, I’ll look at the main types of sports bras and the materials that are used to make them. Then we'll be able to talk about what you need to be seeking in your sports bras. 

Thanks for reading! If you want to learn more about the custom bras I make, sign up to the Queen of Cups Lingerie mailing list. If visual is more your thing, follow us on FB and Instagram (@queenofcupslingerie).