“It’s like wearing a cactus, painful, distracting and never a vibe.” Fitness presenter Dannielle Lally says wearing an ill-fitting sports bra can sabotage any workout. It’s not just the discomfort, science suggests badly fitting bras can seriously derail your training progress.

Every day millions of movers suffer through their workouts in an ill-fitting bra. A survey of UK female athletes, found 51% experienced breast pain during their training and 29% believed an ill-fitting bras affected their performance. When these athletes were individually assessed and fitted with a sports bra, 97% of those wearing the prescribed bra reported greater comfort, fit and support, while 17% said it significantly improved their performance.

Running better, becoming more agile, improving posture and moving with greater confidence … these are some of the performance benefits that go hand-in-hand with a well-fitting sports bra.

Amy Lu wearing an adidas sports bra during BODYPUMP strength training

The importance of a well-fitting sports bra comes down to the fact that breasts are such a unique part of our anatomy. There are no muscles in the breast, simply glandular and adipose tissue, blood vessels and fragile connective tissue (known as Cooper’s ligaments). This means our breasts have minimal internal support, so when the body moves there is little to control how our breasts move too.

And they can move a lot. Together with breast health expert, Professor Joanna Wakefield-Scurr, and the University of Portsmouth, adidas found that when you run your breasts can move up to 19cm and could experience the same G force as an F1 driver!

Such significant movement can overstretch the breast tissue which is thought to cause damage and breast pain. When breasts are insufficiently supported during exercise it affects the body’s kinetics, compromising physical performance. For example, researchers found recreational runners seemed to adopt inefficient technique and take shorter strides when wearing unsupportive sports bras. According to a recent study, simply starting to wear the right sports bra could increase running performance by seven percent. Wearing insufficiently supportive sports bra may also affect the way other parts of your body move. Some believe it forces your upper body to work harder so you fatigue faster.

In some cases breathing frequency can be altered, and there is even evidence to suggest that a lack of breast support can affect ground reaction forces, so the impact of landing on the ground is greater, increasing risk of leg injury.

“A bra needs to be a best friend. Any sign of discomfort it’s an immediate red flag.” Dannielle Lally, Fitness Presenter

Anna Murphy, senior manager of brand and product learning at adidas says the most common misconception about sports bras is where the support comes from. “People always assume that most of the support comes from the shoulder straps, but that’s not the case. The underband is where 80% of a sports bra’s support comes from.” With this in mind, checking the band fit is the first priority, because there’s no point in checking the rest of the bra if the band’s not right.

Fit check: 5 steps to check your sports bra fit

  1. Take two fingers, place them under the underband and run them around the band. If you can do this in comfort it’s a good fit. If you can fit three fingers or more under the underband you probably need to go down a size.
  2. After checking the underband, check the cups. If there is any spillage at the top or sides the bra is likely too small. If there is any gaping in the fabric the bra is likely too large.
  3. Next, check the side seams and make sure they sit behind the breast and not on the breast tissue which can cause discomfort.
  4. Look at the central bit of the bra between your breasts. The closer that is to the body, the better the fit.
  5. The final check is the straps. How firm straps feel is a matter of personal preference, but the most common recommendation is to be able to comfortably fit two fingers under the strap.

Top tip: When trying on a new bra always fit it on the loosest setting. This allows you test the fit at its biggest. You can always adjust to a tighter setting after a little bit of wear and tear.

Watch and learn: Get more sports bra fitting tips from adidas


Stylist Daisy Uffindell, works with fitness professionals from across the globe to help them look, feel and perform at their best. She says it’s surprising that so many people suffer in ill-fitting sports bras (adidas believe up to 90% of women wear the wrong size) as it doesn't need to be that way. “You can choose between high, mid, or low support to align with specific activities and lifestyles. Brands like adidas offer such a comprehensive size range, accommodating cup sizes from A to E, and extending into plus sizes, so it’s easy to find a sports bra that suits the activity, feels comfortable, and fits properly.”

High Support Bras:

“High-support bras, like the adidas TLRD High-Support Bra, are specifically designed for high-intensity and strength training. Utilizing silicon technology, this bra offers excellent shaping and support.” Uffindell adds, “The convenient Zip Front detail ensures a swift and efficient dressing experience and you can customize your comfort and fit with the adjustable straps, allowing you to tailor the bra to your preferences.” What's even more impressive …. This sports bra is crafted from 70% recycled content, Uffindell believes this exemplifies adidas' commitment to addressing the issue of plastic waste and contributing to sustainable solutions.

Mid Support Bras:

Uffindell says the range of Medium Strength sports bras by adidas snugly fit like a second skin. “They feature different padding options, from removable to encapsulated, so there is an option for every preference. Another benefit is the double-layer power mesh lining – so you get steadfast support – even during the most demanding high-intensity workouts – while the moisture-absorbing fabric keeps you feeling dry and comfortable, effectively managing sweat and enhancing your overall workout experience.”

Light Support Bras

“Light support bras are ideal for low-impact activities like yoga and Pilates says Uffindell, who believes the adidas All Me bra offers a perfect blend of comfort and performance. “It’s crafted from a luxuriously soft high-performance fabric and I love the vibrant colors and patterns. Whether worn under a singlet during a walk or on their own at a yoga class, these bras add a touch of style to your fitness wardrobe.”