Breasts move far more than bras are designed to cope with, according to a study by Portsmouth University scientist Joanna Scurr. And they also bounce more during exercise - up to 21cm rather than the 16cm measured in past studies. Bras are designed to stop breasts bouncing, but Dr Scurr's study shows that breasts also move side to side and in and out, and that breasts move as much during slow jogging as they do at maximum sprint speed. Dr Scurr is working with manufacturers vying to design a bra that will lessen movement in all three dimensions and reduce the discomfort suffered when exercising.