Photo: Jens Mortensen

The first sports bra was two jockstraps sewn together. Thirty-one years and several design advances later, many women still aren't getting enough support, because until recently, scientists had never actually analyzed the manner in which breasts bounce. In a three-year study, British exercise scientists discovered that breasts don't just swing up and down but also move in and out and left to right, forming a figure eight pattern. Most bras stop only up and down movement, which could be part of the reason more than half of women suffer breast pain during exercise, says study researcher Joanna Scurr, PhD, of the University of Portsmouth.

One solution, she says, is encapsulation, a style of sports bra that contains each breast in a separate cup (most sports bras just compress breasts). The right bra can reduce breast pain for about 80 percent of women, Scurr says.

See 3 sports bras that will give you the critical support you need