Anthony Joshua claims he has adopted a “prison mindset” and become even more dedicated in his search for redemption against Andy Ruiz Jr in Diriyah, Saudi Arabia, on Saturday night.

Joshua said he spent his 30th birthday in digs in Sheffield, has cut out salt and invested significantly on top‑quality sparring partners in a bid to win back his title.

The former WBA, IBF and WBO heavyweight champion said he has the same “lockdown” attitude he had as a youngster after nearly going to jail – when he prayed for a second chance at life – into his preparations.

“When I went into boxing, I was getting into a lot of trouble,” Joshua said. “I had a major court case and I prayed: ‘God, if you give me a second chance at life I will make all the changes in the world.’ When I beat that court case, I got into boxing and I focused.

“Same thing with Ruiz, give me a second chance at life and see what I can do. I just dedicated myself. I said I would put myself on a 15-year prison sentence to boxing and have that focus.”

That was in 2008 but when it was put to Joshua that he might retire in 2023 he replied: “I could go on longer. It’s just a mindset, a prison mindset, like a military mindset, lockdown. Training, focus, sleep. You have to have that mindset. You have to be in that regimen.”

That includes celebrating his birthday at his digs in Sheffield where he talked to his nutritionist Mark Ellison about training. “I live boxing, I live it, that’s all I do,” Joshua said. “I have a lot more energy now I am no longer focused on any other opponent than Ruiz.”

Joshua has also corrected the failings of his first camp against Ruiz, when he lacked sparring partners who could replicate the Mexican-American’s style and paid the price when he was stopped in the seventh round.

“Sparring is important because it is the closest thing you can get to the fight,” Joshua said. “We don’t always want to do it because it is a big cost but it’s the best way to prepare. They throw everything at me, if I do 12 rounds then it’s with five different people back-to-back and I am dealing with every shot coming at me.

“Ruiz doesn’t get enough credit for his jab. We need to be prepared for that, which is why we got so many sparring partners in.”

Joshua has also been speaking regularly to Wladimir Klitschko, who has given him “tonnes of advice” on cutting out salt, improving his hydration and how to prepare his body better. “It’s almost good that I lost because all of the sparring partners are coming out of the woodwork now, no one wanted to spar me before,” Joshua said.

“Klitschko told me it would happen, he said he could only get good sparring after he had lost. It’s ended up like a blessing because everyone wants to come to the gym now. When we lace the gloves up now there is no holding back.”

Joshua also denied claims from his rivals, including Tyson Fury, that he had fallen out of love with boxing. “I still enjoy it 100%, because I am getting better all the time,” Joshua said.

“You have someone like Vasyl Lomachenko, who is great but then you have some who get better with every fight, like Canelo Álvarez, and that is what I am. You are going to see me get better every step of the way. One loss can’t strip your skin off overnight, when you put your solid foundations in, one chip in the brick can’t destroy the whole building.”

Joshua said he has watched the first fight repeatedly in slow-motion, looking for how he could correct his mistakes. “Until he caught me, I was beating him to the punch,” he said. “They are all quick, but first two or three rounds I was beating him to the punch. He got hurt, I just have to keep down this time.”