New science says the size of your breasts may dictate how you exercise. We look at the biomechanics and beyond.

By Mary Anderson
July 09, 2019
Christopher Malcolm/Getty Images

How big of a factor are breasts in one’s fitness routine?

About half the women with larger breasts in a study from the University of Wollongong in Australia said their breast size has affected the amount and level of activity they did, compared with seven percent of women with small breasts.

Given those stats, researchers found that, yep, “breast size is a potential barrier to women participating in physical activity.”

Psychology comes into play too, says LaJean Lawson, Ph.D., the director of the Champion Bra Lab, who treadmill tests women of all sizes.

“One DD tester told me she never exercises in public because she doesn’t want people looking at her breasts moving,” she says. (Related: Why Every Woman Should Know Her Breast Density)

The Butterfly Effect

What we think of as bounce is not just an up-and-down proposition. As you run, each breast moves in a butterfly pattern—tracing a sort of 3-D infinity symbol with up-and-down, side-to-side, and backward-and-forward motions. (The latter is caused by a brief deceleration of the body upon foot strike, followed by an acceleration when you push off the ground.)

An unsupported A cup might move an average of four centimeters vertically and two millimeters side to side; a DD, by comparison, can travel 10 and five centimeters, respectively. And there are a lot of nerve endings in breast tissue that can register pain and cause you to pull back on your intensity. (Related: How Working Out Changed After My Double Mastectomy)

What You Can Do About It

Lawson’s research shows that the right sports bra can reduce movement by up to 74 percent. Look for separate, nonstretch cups and adjustable, wide shoulder straps. You can even double up and wear two bras at once for extra support, Lawson says. (Here's more on how to pick the perfect sports bra, according to women who design them.)

As for the mental side? “You have to approach bounce as natural and happening to everyone,” says plus-size model Candice Huffine, the creator of Day/Won size-inclusive activewear.

“I used to think my body wasn’t made for running," she says. "Then I tried it. Sure, my breasts require extra work and artillery to secure them comfortably, but in no way would I let them hold me back from crushing my goals." (Keep reading: Beginner Running Tips from Body-Positive Model and Marathoner Candice Huffine)

Shape Magazine, July/August 2019 issue
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