Researchers from the University of Portsmouth in England recently attached reflective markers to the breasts of a group of female runners to test whether breast movement altered running form, NYT reports.
Researchers had the women jog along the track while wearing several different bras, or none at all. They then charted the trajectory of the women's breasts utilizing infrared cameras.
They found that breast sway did in fact have a significant on womens' running. When the runners were braless, their strides changed and they landed more heavily. As the breasts swung from side to side, so did the women's overall weight. Over time, the researchers hypothesized, the extra forces could lead to the development of a host of stress-related injuries.
Typical sports bras fall into two categories. They either cradle each breast in cups, known as encapsulation, or they smoosh the bosom against the chest, known as compression. Finding the best type is more common sense than technical, says Jenny White, a doctoral student at the University of Portsmouth and the study's lead author.
"Find a bra that feels supportive," White said. "Jump up and down in the changing room and assess how much movement occurs. The band should be firmer than an every day bra but should not dig into your skin." All in all, "if the bra is uncomfortable, then this is probably not the bra for you."