Australian women have less free time for exercise as men work out on the borrowed time of their partners.

Researchers at the Australian National University analysed data from about 7000 households with heterosexual couples aged 25 to 64.

It found men were working out on the borrowed time of their partners as women "squeezed" time to take care of their health between work and the family.

"This is a major problem for women's health and fitness," researcher Lyndall Strazdins said.

"Every hour a woman works takes away from her free time but that doesn't happen to male counterparts.

"Men work long hours and seem to borrow time from their female partners to fit in exercise."

Professor Strazdin warned that as people faced tighter work-life balances globally, there was rising disease burdens from cardiovascular to cognitive problems.

About one in three coupled men had time for exercise, which was considered to be more than three moderate or intensive 30 minute exercises per week.

Only 28.6 per cent of women found the same amount of time for working out.

The more women worked, increased family commitments or faced rigid work hours, the less time they had to exercise.

Prof Strazdins' research found when coupled women added 10 hours to their working week, only 22.6 per cent had time for exercise.

But if coupled men added 10 hours to their working week, their time for exercise only feel from 34 per cent to 32 per cent.

The more flexible their female partner's working hours were, the more males were to work out.

"When men work long hours it appears to have no impediment on their physical activity, nor do the hours worked by their female partners," Professor Strazdin said.

She said work hours needed to be capped, including at home, with men and women both given enough time for exercise.