Rather than your intense cardio, pilates is an exercise that focuses on stretching and muscle strengthening and it's become a big hit with our famous faces - including the likes of Reese Witherspoon, Amanda Seyfried, Hilary Duff and Cameron Diaz.
Now Frankie is jumping on the bandwagon, telling the Mail Online: "It's the one that works for me and the baby."
Ahead of her pregnancy, Frankie had danced up a storm on Strictly Come Dancing with partner Kevin Clifton, finding herself in the final three. The series was later won by Caroline Flack.
Following the show, the Saturdays star admits she was hoping to maintain the high level of fitness that she had developed on Strictly, but falling pregnant soon meant she couldn't.
Instead, Frankie had to find new ways to stay in shape. She added: "It's hard being pregnant... I took a break and very slowly got into pilates. People think it's easy, but I made Wayne [Bridge] try it and it was hilarious because he kept complaining about how difficult it is!"
Who knew, eh?!
26-year-old Frankie is currently expecting her second child with husband and footballer Wayne, announcing their happy news earlier this year.
But due to a severe bout of morning sickness, the starlet's baby announcement was bittersweet as it meant she had to pull out of the 'Strictly Come Dancing Live Tour'. Understandably, she was gutted to be missing out.
Instead, Kevin was joined by Rachel Stevens on the road and Frankie claims she was pleased the S Club 7 star was drafted in as her replacement - even if she was a little bit jealous at first.
"I won't lie – I was territorial. Before I knew it was Rachel who would be my replacement I remember saying to Kevin that I didn't want him doing our dances with anybody else and he promised he wouldn't.
"Looking back, it was ridiculous, but as soon as I knew it was Rachel I was happy. There was nobody better-suited for the job."
Famous celebrity mum and daughters!
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!