Joanna Scurr, from the University of Portsmouth on England's south coast, conducted biomechanical studies on 70 women of various bust sizes and found that breasts moved up to 21 centimetres (8.2 inches) during sport.
Previous studies had measured movement at 16 centimetres, she said.
But while sports bras are designed to prevent breasts bouncing, the lecturer in sports and exercise science also found there was side to side and in and out movement and that breasts moved as much during slow jogging as sprinting.
Scurr is currently working with bra manufacturers to create better support for women to lessen movement and reduce the pain felt by many women during exercise.
"Breast size and pain caused by exercise can be a real barrier to women doing exercise," she said, adding that a women with small breasts can just as easily be prevented from taking part in sport due to breast pain.
"If women wore the correct form of support, if we can get that right, the use of pain medication is reduced and women can be active and lead healthy lives."