I couldn't resist.

"I think Sienna might be a bit faster than you," I playfully (stupidly and incorrectly) suggested to Chadwick Boseman at the top of our recent interview in Los Angeles.

"I thought you were struggling to keep up with her."

The super fit Boseman, arguably the hottest actor in Hollywood after Marvel's Black Panther earned more than $US1.34 billion ($A1.97 billion) at the global box office last year, quickly defended himself.

"I don't think so," he replied with a smile.

Boseman and Sienna Miller star in the new action-crime-thriller, 21 Bridges.

The action does not stop.

Boseman plays NYPD detective Andre Davis in the film.

He is paired with tough, Brooklyn-bred narcotics detective Frankie Burns, played by Miller.

The detectives attempt to hunt down two thugs (played by Taylor Kitsch and Stephan James) who massacre eight NYPD officers in a botched robbery.

The thugs flee to Manhattan and in a desperate plan to trap them Davis orders all 21 bridges and other tunnels and routes into and out of the island metropolis closed.

The sealing off of Manhattan can only last a few hours, so Davis, Burns and a huge contingent of law enforcement officers who flood Manhattan are in a race against the clock.

Burns and Miller are always on the move and at times are on foot.

Miller, the US-born, English-raised actress, is almost unrecognisable as the roughed up Burns and in the action scenes you might think she would struggle to keep up with the actor known worldwide as the superhero Black Panther.

Miller is no slouch.

"She is fast," Boseman adds.

Miller was sitting beside Boseman in the interview and keen to make sure the truth was known.

"The first time we did a running scene he paced it out for me," she explained.

"He's definitely faster but I kept up.

"He was like, 'OK. We can go'.

"I have a little pace on me but I'm a sprinter. I can't sustain it."

An action film like 21 Bridges is the obvious next step for Boseman, who has proven to be box office gold and had a pile of scripts to choose from for his next role.

He slipped back into his Vibranium armoured Black Panther suit to help propel Avengers: Endgame to be the highest-grossing film of 2019 with almost $US3 billion in takings.

Boseman also proved his acting chops in recent years playing baseball icon Jackie Robinson in 42, music great James Brown in Get on Up and US Supreme Court justice Thurgood Marshall in Marshall.

"I saw an opportunity to do something I have seen other actors that I love do," Boseman, who also produced 21 Bridges, said while explaining why he chose the action film.

"It's an old school film with action and characters.

"Why wouldn't you do it?"

21 Bridges is playing in Australia.

Australian Associated Press