Is your bra holding you back? It’s one of the most overlooked pieces of workout kit, yet new insights suggest your sports bra could be influencing how your body moves and performs.
For many women, the sports bra is a functional essential — something to pull on before a workout without a second thought. Yet despite its everyday role, it remains one of the most overlooked and misunderstood pieces of performance wear. In fact, research consistently suggests that as many as 80% of women are wearing the wrong size.
It’s an issue I’ve become all too aware of while training for my first marathon. As the mileage has increased, so too has an unexpected problem: chafing. What started as mild irritation has, over longer runs, become increasingly uncomfortable — at times painful — revealing just how much strain a poorly fitting sports bra can place on the body over distance.
The consequences are typically framed in terms of comfort. Chafing, shoulder strain and lack of support are widely recognised issues. But as sports science continues to evolve, attention is shifting towards how these seemingly minor fit issues may influence the way the body moves and performs.
Understanding what constitutes a well-fitting sports bra, and what happens when that balance is off, has become an increasingly important part of the wider discussion around women’s performance and sportswear design.
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Can wearing an ill-fitting sports bra hurt athletic performance?
Nicki Hall, product development manager at Gymshark, explains that the underband plays a far more significant role than many realise. “The underband provides around 80% of the bra’s support,” she says. “Because of this, it should be snug enough to stay level under stress, but never so tight that it restricts movement or breathing.”
Recent research suggests that this balance is more critical than previously understood. A study found that tighter underbands can alter breathing patterns, causing runners to adopt faster, shallower breaths. In contrast, slightly looser bands allowed for more natural breathing, indicating that excessive compression may be working against the body during exercise.
“There’s a common assumption that tighter means better,” Nicki adds. “But if the band is too tight, it can limit how your ribcage expands, which may impact your breathing —especially during high-intensity workouts.”
The implications extend beyond respiration alone. When breathing becomes restricted, the body often compensates in subtle ways, affecting posture and movement patterns. “A misfitted band, whether too tight or too loose, can impact posture and movement,” Nicki says. “And when your posture is compromised, your breathing and overall performance can be affected too.”
This connection is reflected in broader research. A study by Brooks Running Co in conjunction with the University of Portsmouth found that inadequate breast support can reduce stride length by up to four centimetres. Over longer distances, these small inefficiencies accumulate. Engineers at sportswear brand Maaree estimate that this could result in an additional 965 steps over a marathon — equivalent to approximately 0.55 miles, or around seven extra minutes added to a finishing time.
For Mari Thomas-Welland, founder of Maaree, these findings reinforce what she has observed throughout her career. “When your body is compensating for a lack of support — whether that’s through altered posture, restricted breathing or inefficient movement — it inevitably affects how you perform,” she explains. “Even small changes can have a cumulative impact, particularly over longer distances.”
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The innovation changing sports bra design
For Mari, these limitations in traditional sports bra design became clear early in her career. Having studied Sports Engineering at Loughborough University and worked on testing for global brands including Nike and Lululemon, she identified a gap in how support was being delivered.
“Through testing, it became apparent to me what was missing from the market,” she says. “Traditional sports bras focus heavily on compression or encapsulation, but they don’t always address upward motion in the most effective way.”
Her response was to develop the ‘overband’ — an additional structure designed to reduce upward breast movement. “When running in an unsupportive bra, you naturally place your hands over your chest to stop movement,” she explains. “The overband does the same thing: it provides that extra level of control without needing to overtighten the underband.”
Signs you’re wearing the wrong sports bra
Recognising the signs of a poorly fitting sports bra is essential. According to Mari, discomfort is often the first indicator.
“A bad back is a core sign,” she says. “Your bra is meant to support you from below and hold your breasts up, but a bad or ill-fitting bra will be held up from the straps instead. This affects your posture — you start to hunch — and that’s when back pain can develop.”
She also points to shoulder strain as a common issue. “If you’re seeing indents in your shoulders or feeling pressure there, it’s a sign the straps are taking too much of the load, which they’re not designed to do.”
Breast discomfort is another clear signal. “If your breasts hurt during or after exercise, it’s usually because they’re not being supported properly. There’s too much movement, which places strain on the tissue.”
Chafing, meanwhile, may indicate the opposite issue. “If the bra is too big, the fabric can rub against the skin, causing irritation. A good sports bra should sit securely and minimise friction.”
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How to find a sports bra that fits properly
Achieving the correct fit isn’t simply a matter of comfort, but of performance. Experts recommend opting for sports bras that are sized by both cup and band, rather than generalised small, medium or large categories, which often fail to account for individual proportions.
Nicki advises taking a considered approach to the fitting process. “When you’re trying on a sports bra, check how the band sits,” she says. “It should feel level across your ribcage and stay in place without riding up.”
Movement, she adds, is just as important as static fit. “Try a few jumps or a light jog on the spot. The band should remain secure without digging in, and you should still be able to breathe easily.”
At the core of a well-fitting sports bra is balance. While straps are often tightened in an attempt to increase support, they contribute only a small proportion of the overall function. The majority comes from the underband, making its fit critical.
“You should tailor your sports bra to the impact level of your workout,” Nicki explains. “For running or high-impact training, I’d recommend bras that pair a sturdy underband with structured cups, as they help you feel secure during high levels of movement.”
However, support should never come at the expense of restriction. “The goal is always that ‘just right’ fit,” she says. “The band should feel snug, sit level across the ribcage, and still have around one to two centimetres of give. That allows you to move freely while maintaining support — and breathe comfortably.”
For those unsure of their size, virtual fittings are becoming increasingly accessible. Brands such as Maaree offer guided online appointments, helping women measure accurately and find styles suited to their needs.
Feature image: Pexels
