You may be surprised to know that researchers actually study breast motion. Breasts do more than bounce up and down. They also bounce from front to back and from side to sideand even in a figure-eight pattern. And the bigger the breasts, the more momentum they generate. One study found that DD-cup breasts move more than eight inches vertically during running.
The key to banishing the bounce lies in the design, fabric, and fit of the bra. Bras with separated cups (encapsulation design) reduce breast motion better than bras that flatten the breasts against the body (compression design). Thats because its easier to control two smaller masses than one large mass. Some bras combine aspects of both designs. A wider band and higher neckline also help limit breast motion. High-tech sports bras often contain a mix of fabrics that wick away sweat and allow for support and stretch in the right placessome horizontal stretch, for example, but limited vertical stretch and limited stretch in the straps. Beware of things that may chafe: zippers, uncovered fasteners, and seams in problematic places.
Fitting large breasts into sports bras is a growing business. Most women dont choose regular bras that fit properly, let alone sports bras. Sporting-goods and department stores often have trained staff to help. There are also many web resources. Title Nine, for example, gives graphic directions on how to size a bra, has its own "barbell" system that rates a bras degree of support, and even has "bra coaches" you can call; HerRoom provides a downloadable tape measure and has "bounce-test" videos of bras in action.
Many websites give reasonable, if not somewhat obvious, tips (that apply to all bras, not just sports bras): Your breasts should fill the cups but not overflow them; an underwire should encircle your breast but not poke or pinch it; the lower edge of the band should fall below the shoulder blades; the band should be snug but with enough room so that you can run your finger under it; the center panel of an encapsulation bra should lie flat against your breastbone; straps should not fall off your shoulders or dig in too tightly (its the band at the bottom, not the straps, that provides most of the support).
When trying on a sports bra, do a warm-up test. Jump, bend, and jog (in place in the dressing room, if thats the only option). If buying over the Internet, ask about the return policy. High-impact activities, such as running, aerobic dance, off-road cycling, and horseback riding, require the most supportive bra, of course. But if you are large-breasted, you may need a high-support bra even for walking and other lower-impact activities.