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In the days before the London Marathon last year, scientists from the Research Group in Breast Health at the University of Portsmouth in England approached female racers at the event’s registration center and asked them to complete an anonymous questionnaire about their exercise habits and breast health.

Phys Ed Gretchen Reynolds on the science of fitness.

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Sore breasts are a common experience among women of all ages and sizes, athletes and nonathletes alike.

But scientists had not examined whether and to what extent exercise contributes to breast pain and, conversely, whether and to what extent breast pain alters how women exercise.

So they surveyed almost 1,300 of the women registered for the race and learned, as their new study, published in March in The British Journal of Sports Medicine, makes clear, that exercise does significantly impact breast pain and vice versa.

It should surprise no one, of course, that exercise influences breasts, just as it does virtually every tissue in the male and female body.

Female breast tissue is unusual, however, being weighty, even in small-breasted women, but with little natural anatomical support. As a result, unconstrained breasts move independently when a woman does, and that movement is exacerbated during exercise.

Earlier motion-capture research by the Portsmouth scientists established that unsupported female breasts — that is, those not contained within a bra — oscillate as much as eight inches in space when a woman runs, and not just up and down, but also side to side, forward and backward.

Even when the volunteers wore a standard sports bra, the scientists found their breasts often continued to sway considerably during running.

But whether this breast motion was linked to later soreness was unclear.

Which is why the researchers now set out to examine the real-world consequences of being an active woman and having sore breasts.

“It is an important quality of life issue for women,” said Nicola Brown, a member of the Research Group in Breast Health at Portsmouth, a lecturer in exercise science at Saint Mary’s University College in London and the lead author of the study.

It is also an issue with too many dimensions to effectively study in a single laboratory experiment, so the scientists decided instead to survey a cross section of active women. And contrary to popular belief, a cross section of active women is what the registration roll of a major marathon conveniently provides.

“Some people have the perception that female marathon runners” are all slender and boyish, as elite racers often are, “and don’t have breasts,” Dr. Brown said, but she and her collaborators focused their study on the London Marathon’s “mass-participation runners, who are a variety of shapes and sizes,” she said.

When the scientists analyzed the surveys from these runners, they found that they had data about women with 56 different bra sizes, from an AA cup to an HH and chest-band sizes from 28 to 40 inches. The women ranged widely in body weight, too, with the average being about 148 pounds.

More than 90 percent reported that they always wore a bra, including during exercise.

But these active women were not immune from breast pain. More than a third reported that their breasts were frequently were sore, although not necessarily because of exercise. Sore breasts most commonly were because of hormonal changes associated with the menstrual cycle, the runners reported.

The incidence of breast pain was highest among the women with the largest breasts. More than half of those wearing an F cup or larger reported frequent breast pain. But smaller-breasted women also were affected; about 25 percent of those who wore an A cup or smaller said that their breasts often were sore.

Motherhood reduced the likelihood that a woman would report breast pain, perhaps, the authors speculate, because pregnancy and breast-feeding alter the composition of the breasts.

What the researchers found particularly striking was that, for many of the women, exercise induced or aggravated breast soreness and, in consequence, breast pain often altered how the women trained. About a quarter of those with sore breasts said that they reduced the intensity of their workouts when their breasts hurt — walking in lieu of running, for example — while others skipped exercise altogether.

In aggregate, Dr. Brown said the results suggest that exercise-related breast pain can compromise the quality and quantity of physical activity for many women.

Of course, many of us might consider that a self-evident finding — anecdotal evidence suggests that my friends and I complain all the time about how our breasts feel when we’re running. But this is the first study to formally examine and validate the issue.

It also, Dr. Brown said, “highlights the importance and significance of research into the treatment of breast pain.” A well-fitting, supportive bra, she said, has been shown to lessen breast pain in about 85 percent of women with the condition. But a large number of women, including by inference many of the London runners, are not wearing the right bra.

The Research Group in Breast Health has published a handy online guide to bra fitting. But far more research is needed into sports bra design, Dr. Brown said, an undertaking that she hopes will progress rapidly, having herself just completed her first marathon and been hampered occasionally during training by sore breasts.