Men focused on fitness are borrowing time from female partners while women's health suffers when work hours increase, new research has shown.
Data from more than 7000 households, made up of heterosexual couples aged 25 to 64, found a women's day had "no give" for exercise while men's time was "elastic", according to an Australian National University study.
Of those studied, 34 per cent of men participated in more than three physical activities for at least 30 minutes per week, compared with 28.6 per cent of women.
The study found if women increased work time by 10 hours per week, or two hours per day, that number reduced to 22.6 per cent.
In contrast, when men increased paid work by 10 hours per week, the number who were physically active only dropped by two per cent - to 32 per cent.
Jo Legge-Wilkinson, president of Canberra Runners, trains with a majority female group, mostly in their forties.
She said their strategy for juggling work, children and home duties meant exercising first thing in the morning.
Ms Legge-Wilkinson said while most women join initially for physical fitness, prioritising exercise quickly becomes about more than being fit.
"Obviously exercise is really good for your mental health, but also you become part of the community," she said.
"I still go for the physical fitness, but they're my group, they're my team, so being part of that community now is really, really important, particularly for women."
Study author and ANU Professor Lyndall Strazdins said the findings represented a major problem for women's health and fitness.
"Every hour a woman works takes away from her free time, but that doesn't happen to male counterparts," Professor Strazdins said.
"Men work long hours and seem to borrow time from their female partners to fit in exercise."
The study also found men were likely to increase their physical activity when the working hours of their female partners had more flexibility.
Professor Strazdins said this was one of the first studies to show how, hour for hour, women's time for their health was being squeezed to manage jobs and family, whereas men's time for jobs and health was more protected.
"Men having more time for exercise and more flexibility in their work time is playing out in women's bodies," Professor Strazdins said.
"Women are giving their health and wellbeing to their male partners."
Professor Strazdins said public health measures designed to increase exercise needed to take gender inequality into account, including the very different circumstances women face with work-life balance.
"There is currently a global exercise drought, and this is pushing huge disease burdens from the cardiovascular to the cognitive.
"We need to cap work hours on the job, and even the sharing of care hours in the home - for men and women to both have enough time for staying healthy."
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