Open this photo in gallery After their midlife fitness pact, Tracy Isaacs, left, and Samantha Brennan say they’re happier, stronger and faster than they’ve ever been, despite little change in their body weights. Ruth Kivilahti/Ruthless Images

Just before their 48th birthdays, Samantha Brennan and Tracy Isaacs made a pact to reach their peak fitness by the time they turned 50. But as philosophy professors and lifelong feminists, the two friends decided to challenge the usual definition of “fit” as synonymous with “thin.”

They started a blog called Fit Is a Feminist Issue – gaining nearly 20,000 followers – and charted a course towards physical fitness that did not include dieting, body obsession or cutesy gym clothes. Within two years, Isaacs went from struggling to run for 20 minutes to completing triathlons and training for a half-marathon. Brennan, an avid cyclist, ramped up her workouts to include CrossFit, rowing, aikido and yoga.

Both say they’re happier, stronger and faster than they’ve ever been, despite little change in their body weights. The pair describe the connection between physical activity and valuing their own bodies in their new book, Fit at Mid-Life: A Feminist Fitness Journey, which was released April 14.

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Brennan, dean of the College of Arts at the University of Guelph, spoke to The Globe and Mail about why midlife is an ideal time to test the limits of one’s physical potential and redefine what it means to be fit.

What is feminist fitness?

It’s an invitation to enjoy your body, enjoy physical activity and try to set aside the ideals about what ‘fit’ looks like. If you do a Google Images search for fitness, you have to scroll through pages and pages before you get past images of women in their teens and 20s who are thin, physically able and white. We’re interested in fitness that includes people who are older, people who have physical disabilities, people who aren’t sure where they belong on the gender binary.

Open this photo in gallery Fit at Mid-Life: A Feminist Fitness Journey was released on April 14.

Many women have mixed feelings about feminism, yet your blog has really taken off.

I think people like the community, they like the conversation in the context of something you might not have thought of as feminist before. Physical activity for women is not a trivial issue. Beyond the health implications, there is something about being a physical person and learning to inhabit your body that leads to more self-confidence. And when you look at things like women’s professional success, or women’s political success, I think those things are probably connected.

What are common barriers to fitness that women talk about?

Lack of time is one. In the book, I talk about women on my soccer team who were kind of sneaking out of the house to play soccer, claiming they were off to do groceries, because they felt guilty about leaving the kids home with dad. Women often sacrifice exercise because we’re busy doing a lot of the childcare and a lot of the elder care while working full-time. Also, lots of women think they have to lose weight before they put on athletic clothing – it’s a huge deal for people. I was horrified to read about women in England who say they exercise in the backyard shed because they’re too embarrassed to be seen in public, or the number of women who say they run at night because they don’t look like a runner and don’t want people to make comments.

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You describe yourself as overweight, yet it sounds like you’ve always had a positive body image.

I have. Among my friends, it’s often women who are closer to the ideal who suffer the most, because they want ‘in.’ Those of us who have been outside of the mainstream most of our lives – it’s not been a thing on offer.

How can feminist fitness replace the dream that some day, with enough effort, we can become the slim, gorgeous people we see in ads?

First of all, that dream doesn’t work, and I think it can be a pretty miserable place to be. So what instead? Living our lives now, finding sports and other ways of movement that are joyful and pleasurable. I think that happens when you’ve got a community of people to do it with, and it’s connected to the rest of your life, rather than being this drudgery that you’ve got to squeeze in. I’m often riding bikes with friends or canoe-camping with my kids – it’s the fun part of my life.

Why is midlife a great time to redefine fitness?

Often as we approach 50, we have this one sport or physical activity that we love. Before the challenge, I was pretty much a cyclist. Then I tried CrossFit, I tried rowing. I’m not a big yoga fan but as I get older, I’m realizing that flexibility matters – I’m thinking about what’s going to help me stay active, not just at 50 or 60 or 70, but can I still be on my bike at 80? What do I have to do now to make that possible?

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If this book could achieve one thing, what would it be?

It would be loosening up the pressure on women to look a certain way and think of fitness in such narrow terms. I complained to a gym at one point because they had no posters up that weren’t about weight loss. I’m not saying you should have no weight loss messages there – it’s why lots of people come to the gym. But why can’t we have some that are about stretching and flexibility, some that are about your 5K time and some that are about enjoying the company of your friends in your aqua-fit class?