3 things to keep in mind when choosing a runner's sports bra

Support

Your breasts move side to side, up and down, and in a three-dimensional figure-eight pattern while you run. "When we think about how we're trying to control those motions, we're trying to control it from the bottom-up, the top-down, the side-swing, and then we're also trying to hold it back," claims Ruckman. Any bra should aim to produce one of three distinct movement vortexes, according to experts. Basically, you want a bra to restrict breast movement from all directions to avoid chafing under the arms, neck, shoulder, back, and chest pain.

And sure, AA and A cup women should also think about donning a sports bra. According to Ruckman, "science has shown us that no matter how much breast tissue you have, it will eventually start to sag because it is not rooted to any muscle or bone." The unsupported ligament, as well as the breast's fat and fiber, will change more slowly the more you can support them.

Fitting

Visit your neighborhood running store or lingerie store to have a professional fitter take your measurements for the most individualized service. Here's how you measure oneself at home if you have a tape measure, a long length of thread, or both available.

Band size: Measure as tightly as you can beneath your breasts while wearing your everyday bra (or the one that feels most comfortable). If the number is even, add four inches; if it is odd, add five. For instance, if your measurement is 26, your band size is 30. Your band size is 32 if it is 27.

Cup size / Loosely measure the fullest part of your breast, over your nipples. “You want the tape to be loose because you want to make sure that what you put over your breast is encapsulating your tissue and not compressing it down,” says Ruckman. Subtract the initial measurement from the previous step—not your calculated band size—from this number. For instance, if your over-the-breast measurement is 33 and the tight under-band measurement is 27, then 33 minus 27 gives you 6.

Finding your bra size is only the first step. / We recommend buying a few different sizes of the same bra to check for the best fit. You may think you want to size down for more compression, but that puts you at risk for chafing.

The straps and bottom band should fit between two fingers. According to Ruckman, if it's too tight, you'll experience stress and discomfort. You want the bra to be snug enough to provide the necessary support, but not too snug that it starts to distract from your appearance.

If your bra has a hook-and-eye closure, you want it to be loose enough to fit comfortably. This guarantees that you have the remaining hook-and-eye settings to tighten the band when it starts to stretch after a few wears.

Compression vs. Encapsulation

Besides cup and band size, what also factors into the type of bra you should wear is how fibrous your breast tissue is. Runners with denser tissue will likely prefer encapsulation (think underwire or molded cups) over compression. “If you have fattier and less dense breasts, tissue compression will typically feel better because softer breasts compress more easily against the chest wall,” says Ruckman. You don’t need to determine exactly how dense your boobs are; Ruckman’s team has found that runners naturally gravitate toward the kind of support they find most comfortable.