Yes, Your Sports Bra Really Can Restrict Your Breathing

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Running bras have come a long way since 1977, when Lisa Lindahl and Polly Smith stitched together a pair of jockstraps to create the original Jogbra. Current models aren’t just comfortable and supportive; they’re performance-enhancing. Studies have found that more supportive bras reduce oxygen consumption—a proxy for how much energy you’re burning at a given running pace—by 7 percent, perhaps by enabling subtle changes in your running stride.

But they’re not perfect. Surveys find that less than half of women choose to wear a sports bra during physical activity. The most common complaints are that the shoulder straps slip or chafe, and that the bands are so tight around the ribcage that they’re uncomfortable and restrict breathing. It’s this last concern that resonated with Shalaya Kipp, a former Olympic steeplechase runner and—conveniently—an exercise scientist at the University of British Columbia specializing in respiratory physiology. (She recently moved to a new position at the Mayo Clinic in Minnesota.)

In Medicine & Science in Sports & Exercise, Kipp and her UBC colleagues share the results of a study testing whether tight sports bras hinder breathing in runners. A small sample of nine nationally or internationally competitive runners completed a series of treadmill tests while wearing a specially modified version of Lululemon’s Energy sports bra whose underband tightness around the ribcage could be increased or decreased with extra eye-and-hook attachments at the back. The bra was also modified so that a small balloon catheter could be inserted into the underband to measure exactly how much pressure was being exerted as the subjects inhaled and exhaled.

That’s not all. The subjects had another balloon catheter inserted through their nose and down into their esophagus to measure the internal pressures exerted with each breath by their lungs as they ran. This is no joke: Kipp posted an amazing video on Instagram showing her having this catheter inserted, and it’s definitely worth a watch if you want to appreciate what the subjects were willing to undergo in the name of science. The catheter enabled the researchers to calculate the “work of breathing”—that’s the energy used by the respiratory muscles to inflate and deflate the lungs, which can consume more than ten percent of your total energy output during hard exercise.

The running tests were performed in three conditions: once with the subjects’ self-selected preferred bra size; once with the bra tightened; and once with it loosened. The pressure of the band in the tight condition was, on average, 16 percent greater than in the loose condition. Here’s what the oxygen consumption (VO2) during submaximal running looked like in those three conditions:

Going from self-selected to tight didn’t change anything. But going from self-selected to loose reduced oxygen (and energy) consumption. The overall difference between the tight and loose conditions was between one and two percent in most subjects, with an average of 1.3 percent and eight of the nine subjects seeing improvements in the loose condition. That’s not as big as the four percent change from supershoes, but it’s significant. Kipp estimates that a two-percent change in oxygen consumption translates to a three-minute change in marathon time for a three-hour runner.

The reason for the efficiency difference is presumably that the tight bra made the women breathe differently. While running at VO2 max in the tight bra, the women sucked in more oxygen overall by breathing more quickly (57 rather than 52 breaths per minute) but also more shallowly. That work of breathing took 16 percent more energy, which explains why overall whole-body oxygen consumption was higher. There may also be secondary effects: if the breathing muscles are working harder and consuming more oxygen, that could divert oxygen-rich blood away from the working muscles in the legs and elsewhere.

Is this a serious problem? That depends on how tight you wear your bra, and how much you care about a percent or two improvement in performance. If you’re happy with your bra, you can safely ignore these findings. But Kipp cites previous data suggesting that 70 percent of women choose sports bras that are too small for them compared to a professional fit. That figure probably varies widely depending on who you survey, but it’s consistent with the data in the current study, which sees an improvement going from the self-selected size to loose, and no change from self-selected to tight.

The subjects presumably choose tighter-than-optimal bras because they want adequate support—but none of the women in the study reported that the loose condition was uncomfortable or provided inadequate support. One possible explanation, Kipp and her colleagues point out: most women pick their sports bras based on how they feel at rest. None of the breathing parameters that they measured in the new study were affected at rest. It’s only during hard exercise, when the women were breathing hard and inflating their lungs, that the problems emerged. So it probably makes sense to evaluate your sports bra based on how it feels at the end of a workout, rather than how it feels in the store.

Of course, there’s much more to sports bra design than how tight the underband is. The right design will depend on the shape of your body—all the elite runners in this particular study, the researchers note, had small to medium breasts—and what activity you’re doing. There are endless patents (and more than a few patent battles) and numerous competing models that aim to help women thread the needle between insufficient support and excessive tightness. There’s unlikely to be a single perfect solution that fits everyone. But if your sports bra feels so tight that you wonder whether it might be interfering with your breathing, it probably is.

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