It takes a strong man to face his weaknesses, says British actor Idris Elba.

That is why the 44-year-old, who is often described as the ultimate man's man and one of People Magazine's Sexiest Men Alive, willingly put himself in a vulnerable position in the new documentary series Idris Elba: Fighter.

For the show, which airs on Discovery Channel (StarHub TV Channel 422 and Singtel TV Channel 202) on Sundays, he underwent gruelling training sessions over a year in places such as Japan and Thailand to become a professional kick-boxer.

In the finale of the three-part programme, he steps into the ring in London's famous kick-boxing venue, York Hall, for a fight against a younger and more skilled opponent.

An executive on one of the two movies he was filming in between shoots for this series was worried about what the fights would do to Elba's image if he were to lose.

The actor, who was filming The Dark Tower and Thor: Ragnarok at the time, says: "I thought about that for a second and then I was like, 'F*** that, I don't care about that to be honest.'

"This isn't about that. This is a personal journey and, yes, there is the risk of looking weak because I certainly did. If people stop liking me as an actor because of that, then okay. But I think I came out of this a stronger person and, therefore, perhaps an even more desirable actor for hire.

"You do have to tap into and embrace weakness to be strong."

He was giving an interview over the telephone to The Straits Times and other media around the world.

The award-winning star of hit television shows such as The Wire (2002-2008) and Luther (2010- 2016) found himself on the ground many times while training on the show, suffering knee and back injuries, as well as a concussion.

Yet he never backed away from the plan - and the film-makers of his two films had no say in the matter.

"I didn't give them a choice to say whether I can do this or not. I was already doing it by the time I got onto both films. But I was respectful of my day job. As long as I didn't damage my face while filming the movies, then I was fine."

In The Dark Tower, a sciencefiction western based on the series of novels of the same name by Stephen King, Elba plays a knight who is an expert with revolvers. In Thor: Ragnarok, the latest instalment in Marvel's Thor series, he plays Heimdall, the superhuman sentry of the Bifrost bridge.

As soon as filming for the two movies were over, full-on sparring took place.

"I remember a couple of times when my nose changed shape after a spar, and I was like, 'S***.' But ultimately, I started to get proud of my scars - one especially, on my torso, which came from a pretty brutal kick.

"When I see it now, I go, 'Yeah, I survived it.' It makes me feel like I went through something. I know it's a bit weird."

Ask him what his worst fight has been and he sounds surprisingly philosophical. "I think that's a bit too personal to answer because it doesn't include a physical fight."

He says his motivations for doing this series was to prove to himself that he could achieve something, as hard as it would seem. Plus, there was a mid-life crisis to overcome.

Elba, whose production company Green Door Pictures is behind the series, says: "I think my ego was being tested at middle age - like how some people go out and buy Ferraris or motorbikes. I was interested in testing whether my body could withstand extreme training.

"At optimum training, I was more fit at 44 than I was at 18, so that was an achievement."

Every morning for a year, he would wake up at 5am to do a 4.8km run, then it was off to the gym for strength training. Core work was thrown in later, before the actual fight training.

Diet-wise, he cut out carbohydrates and alcohol, consuming mostly fish, chicken and vegetables instead.

He confesses that most of those close to him were puzzled as to why he would want to do anything like this.

"My mum wasn't impressed at all. My mum was really worried. She came to one of the fights and it was pretty harrowing. And it was pretty harrowing for everyone who knew me.

"I had a lot of friends and family at my first amateur fight and they couldn't believe what I was doing. I drew that fight, but I got knocked down in the third round and it was a pretty brutal uppercut that took me down."

His children - daughter Isan, 14, and son Winston, three - were considerably more supportive.

"My daughter was very into it and my son came to training with me. He's in the show - he came to Thailand when we trained there.

"So my kids were into it. They're sort of used to daddy being a bit stupid in that sense, I guess."

Idris Elba: Fighter comes after his Discovery Channel documentary series Idris Elba: No Limits (2015), in which he broke an 88-year-old land speed record in a Bentley.

Inspiring others with can-do spirit

For now, there are no plans to do any more real-life challenge shows, although he says half in jest that he would love to go to space "if Discovery will pay for it".

He is busy enough with all his other gigs - on top of the acting projects, he is set to direct his first feature film this year with Yardie, an adaptation of Victor Headley's 1992 drug-trafficking novel of the same name, which is set in London.

He also plans to make more music - as a DJ, he has several EPs to his name, such as Mi Mandela (2014) and Kings Among Kings (2009) - and hopes to go on a world tour by next year.

Elba, who is twice-divorced and now single, does not remember the last time he took a proper holiday.

"I've sort of always tried to challenge myself and put myself through stressful things, and I think I come out of them a better person," he says.

He hopes that some of that can-do spirit will rub off on other people.

On doing Fighter, he says: "The best part is hearing other people my age say to me, 'Look, I've always wanted to ride bicycles and I've never done that and you know what, Idris, I think I might want to do that now.'"

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•Idris Elba: Fighter airs on Discovery Channel (StarHub TV Channel 422, Singtel TV Channel 202) on Sundays at 9pm.