Australian scientists have created an 'intelligent' bra that monitors the user's activity to determine the most comfortable fit for future underwear.

The bras are being used to look at the nerve damage caused by bad bra fitment and to allow women to exercise in more comfort. They come with sensors woven into the fabric and measure the position of the bra relative to the body, as well as other load factors.

"A consequence of current brassiere design is that the brassiere straps bear much of the load generated by breast momentum during physical activity," say the researchers from the University of Wollongong in the Journal of Biomechanics this week.

"As breast mass increases, breast bounce momentum also increases, placing large loads on the straps and, in turn, excessive pressure on the wearer's shoulders. Apart from strap-related pain, many females, particularly large-breasted women, are restricted from participating in physical activity due to exercise-induced breast pain associated with excessive vertical breast displacement."

The team got two women with a 36D and a 38DD cup size to walk and run on a treadmill. During running vertical movement was measured and ranged from 11 to 68mm.

On analysing the evidence the team found that the shoulder straps bear most of the brunt of this movement and narrow straps cut into important nerves on the shoulders, causing tingling fingers and potentially long term nerve damage.

The researchers say that this kind of study would not have been possible using earlier sensor technology, since it would distort the findings.