Even the most seasoned runner has days when running feels like a slog. Some days you feel like you’re flying along without a care in the world; other days, putting one foot in front of the other can feel like wading through treacle.

Many factors impact how hard (or easy) a run feels, from the weather and fatigue levels to when you last ate. But research shows that exercise – and running in particular – really does feel harder when your boobs aren’t properly supported. And not wearing a decent bra when exercising can cause other issues too, including breast strain and reduced focus.

So, in the interests of becoming a stronger runner, here’s how your bra can affect your performance. 

What happens when you’re not wearing the correct sports bra?

It shortens your stride

According to research by the University of Portsmouth research group on breast health, wearing the wrong-sized sports bra when running can shorten your running stride by four centimetres – meaning that you’re essentially running further than runners wearing the correct bra size.

It’s thought this is due to excessive movement of the breast tissue, which can also cause discomfort and breast strain, as women feel hesitant about really going for it when their boobs aren’t supported – think about the last time you ran up or down the stairs without a bra on, and you’ll know the feeling.

Incredibly, over the course of a marathon, this can amount to running an extra 1.5 kilometres and as anyone who’s ever tried to run a marathon will tell you, every step counts.

It increases your perceived exertion 

“Perceived exertion is essentially the feeling that you are working harder than you actually are when exercising,” explains Charlotte Gill, founder of sports bra brand PeBe.

“For women, this often occurs due to a problem with their sports bra. A poor quality, ill-fitted or low-support sports bra worn during high-impact exercise can lead you to feel like you’re working out harder, especially if you’re using it for high-intensity exercises such as running or HIIT. Your posture will be impacted negatively because you don’t have the right support to cushion the excessive breast movement and this all adds to the sensation of exertion.”

There is also evidence that when breasts are not properly supported, women experience increased upper body muscle activity, meaning you might feel fatigued more quickly – and more tempted to stop running – which has nothing to do with fitness levels or ability. 

It affects oxygen intake

“Studies show high impact support improves oxygen use by 6.9%, meaning you can run faster in a better supporting sports bra,” says Gill. “Ultimately, the more supportive your sports bra is, the more efficiently you’ll be working and the less oxygen you will use when running. This becomes even more vital for D+ cup women, as oxygen usage during exercise is greater the bigger your breasts are.”

Gill also advises checking that your bra offers adequate impact support. “Additionally, if your sports bra does not provide a level of high impact support, you can lose up to 20cm per second against someone running with the same consistency of oxygen but running in a higher impact sports bra,” she explains. “This means if you’re running a marathon, you’re going to be pipped to the post by someone in better support. If you’re running an average marathon time of 4h20m they’ll be 30m ahead of you.”

It can affect motivation and focus

Any kind of discomfort when running can be off-putting, from chafing to blisters, and a poorly fitted sports bra can mean you’re distracted by your breasts. When you’re training hard or in the middle of a race this can make you lose motivation and focus, and can feel frustrating. 

On the plus side, once you’ve found the right bra for you, you can simply focus on your flow – and that well-earned post-run shower and coffee. 

How to choose a running bra

Gill share her top tips for finding the perfect running bra.

1. Get a sports bra that has adjustability on the under band and straps
2. Buy from a brand that has put a lot of research into their designs
3. Make sure it fits! Treat checking your bra size like an annual check-up at the dentist
4. Change your sports bra as often as you would your running shoes; sports bras work hard cushioning impact, so don’t wait until it’s tired and worn out before investing in your next one

Check it’s not too tight

The larger your bra size, the more likely it is that your bra will be highly compressive. While a degree of compression is essential for controlling movement and providing support, if your sports bra is too tight or highly compressive you might feel restricted or ‘pinned in’ with a rib-crushing feeling, adding to the sensation of perceived exertion.

Images: Getty