"Me as her trainer, I sometimes have to protect her from herself," says Bryant Johnson

Ruth Bader Ginsburg Eager to Hit the Gym After Cancer Surgery: 'When Can We Go Back to Training?'

Over the last 20 years, Ruth Bader Ginsburg has survived colon and pancreatic cancer, plus the removal of cancer from her left lung Friday. She’s also had successful heart surgery and recovered from multiple incidences of broken ribs.

How does the 85-year-old Supreme Court justice bounce back again and again — and with such vitality? She credits her trainer Bryant Johnson, who she told the New York Times “has been my physical fitness guardian since 1999.”

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But Johnson tells PEOPLE the secret is the justice’s dogged determination, evidenced by her training twice a week for at least an hour and never saying “I can’t.”

“Even this, she is going through this, she asked me, ‘When can we go back to training?'” he says.

“Me as her trainer,” he continues, “I sometimes have to protect her from herself.”

Their routine, outlined in Johnson’s book The RBG Workout, includes planks, 20 full push-ups, arm and leg work using dumbbells and machines and bodyweight exercises. (You can see her working out with Stephen Colbert in her signature “Super Diva” sweatshirt in the video below.)

“Her attitude is, ‘When is the next time I can work out?’ No matter what, it is, ‘When can we work out?'” Johnson says.

Following Ginsburg’s fall on Nov. 7 that resulted in three broken ribs, Johnson made her rest for a few weeks. They slowly resumed lower-body exercises before working back into a full workout last week.

“The justice is strong,” he says, “and blessed.”

Filmmaker Betsy West, director of this year’s acclaimed Ginsburg documentary RBG, saw the focused Ginsburg working out in her “Super Diva” sweatshirt.

“It was Bryant who pointed out to us her toughness,” she says. “He calls her a ‘cyborg.'”

“He is a fitness trainer for the U.S. Army Reserve and he compares her to young soldiers. He says they ask too many questions — why do we have to do this, why do we have to do that — and Justice Ginsburg, she is dedicated, she does what he tells her to do. He says she is like a machine.”

Ginsburg’s work this week included a training session with Johnson and a vote before the surgery to refuse to let the government enforce President Donald Trump‘s proposed restriction on asylum-seeking immigrants, a 5-4 decision that upheld a lower court ruling.