Margot Robbie's trainer reveals she once did a full workout in her 'Barbie' costume and makeup

• Margot Robbie did a full workout in her "Barbie" hair, makeup, and costume during filming.
• David Higgins, her trainer, told Insider she kicked off her heels and got on the Pilates Reformer.

Margot Robbie fully embraced her role as "Barbie" — even in the gym.

David Higgins, Robbie's longtime trainer, recently spoke with Insider about what it was like to train the "Barbie" cast. And he was happy to share some of his favorite behind-the-scenes memories.

That included the day he saw Robbie kick off her heels and do a full Pilates workout in her "Barbie" hair, makeup, and costume.

"She was dressed up in one of the 'Barbie' outfits, full wig and everything," Higgins recalled. "She jumps on the Reformer and we do a quick 30-minute express workout. She said, 'Don't make me sweaty!'"

"She just needed to move, and that's the beauty of Margot," he added. "She knows her body so well. She knows what she needs to do and will sneak it in when she can. I was talking to her as she's doing whatever she's doing on the Reformer and I was like, 'This is crazy.'"

Higgins, who is also the author of "The Hollywood Body Plan," said he still regrets that he didn't take a photo of the moment, although he did snap a picture after Robbie beat the "Barbie" cast at a plank challenge.

While Higgins took the top spot with a plank that lasted five minutes and 32 seconds, Robbie wasn't far behind after holding her plank for four minutes and 10 seconds.

She beat out costars Ryan Gosling (three minutes and two seconds), Hari Nef (two minutes and 15 seconds), and her husband Tom Ackerley, who clocked in at one minute and 36 seconds.

The "Barbie" cast worked out together during filming, and Higgins said the atmosphere in the gym was always full of laughs — which was different from the superhero movies he's worked on, including "The Batman."

"What was fun about the 'Barbie' movie was, because of the subject matter, it sort of promoted a sense of fun and a sense of levity that other films might not have," he said. "Like 'Batman,' for example, Batman's quite a dark character and that kind of translates into other areas of the film as well, and that was quite an interesting experience. Having Barbie be so pink, it really infiltrated every aspect and every area of the film."

Robbie stayed committed to her role as Barbie throughout filming, implementing mandatory pink days on set, drinking cups of special tea to keep her skin glowing, and doing four days of Pilates per week with Higgins.

"She's always up for everything," Higgins said.