For most of my life, my requirements for a sports bra were purely aesthetic. As a card-carrying member of the small breast society, I never really needed support. I wanted something that looked cute and didn’t cost a fortune. I could run a 5K in a yoga bralette and live to tell the tale.
And then… I had a baby.
For the last nine months of breastfeeding, we’ve been on a wild ride. I’ve been living in soft, clip-down nursing bralettes that prioritize access over everything else. But recently, as I tried to get back into running (yay), I strapped on one of my old cutesy sports bras and realized within three strides that my membership had been revoked.
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Things felt heavy, unsecure and ouchy. I wanted to move and jump freely again, so, I dug into the latest sports bra science (all credit to the incredible Breast Research Australia, directed by Professor Deirdre McGhee) to figure out exactly what I needed now that my equipment needed to be changed.
Here’s the latest on the science I wish I was taught, and the four step fit-check used by professionals to get (quite literally) locked in.
In this article
We happily drop $200 on running shoes to protect our shins and knees, but we treat our sports bras like accessories.
Breasts don’t have muscle. They are made of tissue and fat, supported only by skin and Cooper’s ligaments. According to Sports Medicine Australia, during just one hour of running, female breasts can bounce approximately 10,000 times.
Without proper support, that repetitive strain can lead to breast pain associated with exercise, impacting performance (not to mention comfort).
When your chest isn't supported, your upper body instinctively tenses up. Research shows that a high-support, correctly fitted bra can actually optimize your running economy, upper torso posture, and even alter the landing biomechanics of your lower limbs during running.
The Golden Rule: The SMA states that your breast discomfort during exercise should be 0 out of 10 . If it’s anything higher, your bra isn't doing its job.
The 3 types of bras - and which one you need
I used to think there were just "sports bras" and "regular bras." Turns out, sports bras come in three distinct engineering styles. Knowing the difference saved me from buying another one that didn't work.
1. Crop Top (Compression)
This is the classic "sports top" design. It works by compressing the breasts as a single unit against the chest wall.
Best for: Young athletes, smaller breasts, or low-impact activities like walking where there is minimal bounce.
The downside: Because they lack separation, they often aren't enough for high-impact running if you have a larger cup size. Plus, the straps are usually not adjustable.
2. Encapsulation (Defined Cups)
These look more like everyday bras, with distinct cups that contain and elevate each breast separately.
Design: Look for adjustable bands and straps to optimize the fit.
Best for: Reducing movement by lifting the breasts relative to their bare position.
3. Hybrid (The Powerhouse)
These combine compression (hugging the body) with encapsulation (defined cups) to both elevate and compress.
Design: Often features adjustable straps and bands for a precise fit.
Best for: High-impact activity and larger cup sizes.
The 4-step fit check to do at home
I always thought the straps did the heavy lifting, but it turns out the band should provide most of the support. If you’re relying on your straps to hoist you up, you’re just giving yourself shoulder pain. Here is how to test if your bra fits correctly:
1. The Band Test
The band should feel firm around your trunk. Raise your arms straight up in the air.
The Green Light: The band stays anchored and does not move up and down on your trunk.
The Red Flag: If it slides up or feels loose when you pull it away from your body, it is too big .
2. The Cup Scoop
Scoop everything into the cup.
The Green Light: All breast tissue is contained within the cup.
The Red Flag: If the fabric is wrinkling, it's too big. If you have "double boob" bulging out of the front or near your armpit, it's too small .
Tip: Look for high necklines that cover all tissue.
3. The Strap Tug
The Green Light: Straps should feel firm on your shoulders.
The Red Flag: If they slide off, they are too big. If they dig in comfortably, they are too small .
4. The Wire Check
If your bra has an underwire:
The Green Light: It sits flat against your breastbone at the front and on your ribs near your armpit.
The Red Flag: If the wire sits on top of any breast tissue, it’s the wrong shape.
Girl to Girl PSA: For my fellow nursing mamas: rigid underwires can increase the risk of blocked milk ducts. Stick to high-support wireless or hybrid styles for now.
(Note: The SMA also advises against underwires for contact sports like soccer or martial arts to prevent injury).
The "Two-Bra" Hack
If you’ve tried everything and still feel too much movement, you aren't alone. The SMA explicitly notes that athletes with larger breasts (D+) often need to wear two bras simultaneously to achieve adequate support.
This doesn't mean wearing two old, stretched-out bras. It usually means layering a high-support encapsulation or hybrid bra underneath a sports bra crop top. Think of it as locking everything down with a base layer of separation, then adding a compression layer on top for stability.
Yes, your sports bra has an expiration date
This was a hard pill for me to swallow. I’m still wearing sports bras from 2016. But just like running shoes, it turns out sports bras have a "use by date".
Research shows many women wear bras where the elastic has become overstretched and the material worn out. If the band fits loosely or the straps no longer hold firm, the technical support is gone, and the bra should be replaced .
One final note on age: As we get older, the elasticity of our skin and ligaments decreases, meaning we actually require more support than we used to. If your old favorites aren't working anymore, it might not just be the elastic—it might be that your body's needs have evolved.
