By Michaela Ryan Did you know there's no muscle in your breasts? Skin actually provides the main support. And there's also some support from fine, hair-like ligaments called Cooper's ligaments. "The breasts are not very well supported for the amount of activity we want to do," says Deirdre McGhee, sports physiotherapist and lecturer in functional anatomy at the University of Wollongong. Many women experience breast discomfort if they exercise in an unsupportive bra. It's more common for larger breasted women to experience this, however, it does happen to smaller breasted women as well. A well-fitted sports bra significantly reduces this discomfort. That's because a sports bra limits the amount of breast movement by 50 percent compared to bare-breasted exercise and 30 percent when compared to a lace fashion bra, according to Deirdre's research.