An 'intelligent fabric' with in-built sensors could help bra makers improve the fit of their designs and encourage more women to take up sport according to Australian scientists.

Researchers at the University of Wollongong say the straps of a properly fitted bra can cause pain and even nerve damage, and that exercise is simply too painful for some large-breasted women.

Writing in the Journal of Biomechanics this week, the scientists describe how a special fabric with sensors was used to detect breast movement as women walked and jogged on a treadmill.

The experiment found that the vertical movement of the chest can reach 70mm during vigorous exercise.

It also identified that bra straps bear much of the load generated by breast momentum during physical activity and can affect nerves around the shoulders.

"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," the researchers said.

They wrote: "Our results show that the fabric sensors are suitable to monitor breast motion and brassiere function.

"Brassiere designers will have the ability directly to assess the effects of changes to each brassiere component on vertical breast and brassiere motion using fabric sensors."

Suggested improvements in bra design include limiting excessive breast movement without causing discomfort.