Briton has had chance to step back and reassess after defeat in June while Andy Ruiz Jr may have gone full Buster Douglas

When Anthony Joshua and Andy Ruiz Jr face off on Saturday night in the most controversial world heavyweight title fight for more than 40 years, their rules of engagement will be those of the Marquis of Queensberry and not Mr Olympia. But as the two men touched the scales in Saudi Arabia it was impossible to ignore their respective physiques. Joshua sported a six-pack. His opponent looked as if he had just drunk one.

Joshua has been relaxed all week, despite the mounting criticism from Amnesty International that taking around £60m from a kingdom that has an “abysmal” human rights record, including jailing and executing opponents, was a serious misstep. But the sight of Ruiz weighing in at 20st 3lb, the second highest in heavyweight championship history behind the Russian giant Nikolai Valuev, has surely sent his confidence surging.

Joshua knows there can be only three reasons why Ruiz is now 15lbs heavier than in June, when he discombobulated his senses, and all of us watching, to rip the WBA, IBF and WBO world titles from his waist.

Anthony Joshua insists Andy Ruiz’s burgeoning weight not important Read more

The first is that the Mexican-American believes the dice are loaded against him on a show run by Joshua’s promoter Eddie Hearn and has packed on muscle to ensure the fight does not go the distance. The second is that he was hiding an anvil under the large sombrero he wore on the scales. The least generous interpretation is that Ruiz Jr has gone full Buster Douglas.

It was Douglas who became a byword for going from glory to gluttony, following up his staggering knockout of Mike Tyson by coming in 15lbs heavier for his only world title defence against Evander Holyfield.

The contrast in appearance with Joshua, who weighed in at 16st 13lb – his lightest since 2014 – could hardly have been more stark. Defeat has given the 30-year-old Briton time to reset, to think, to level up. Not only has he trained for 16 weeks for the rematch, sparring for 12 of them – double his usual quota – he has also been zealously studying videos of old fights.

“Ever since I walked into boxing I have been dominating,” he says. “Championships, bosh! Turn pro, bosh! World champion, bosh! And then you never really understand what it is until it’s taken.”

“So I’ve really started studying boxing again. I’ve watched loads of videos, old fights. You learn about tactics, about when to move to the left against an orthodox fighter. Is it dangerous? Is it smart? What is the first art of defensive boxing? I didn’t give a fuck about the science, I just came to fight. Now I’m learning about the sweet science again.”

The vibes are good. Since arriving in Riyadh a fortnight ago, Joshua has held his sparring at a pop-up boxing ring at the British embassy in the Saudi capital. For his last session, he invited 80-100 staff to watch. One onlooker said the fighter looked sensational.

“Behind closed doors I swear I work so hard mentally and physically,” Joshua says. “I spend hours perfecting my craft. As soon as I wake up in the morning I’m listening to stuff that has relevance to mental strength. The minute before I go to sleep I’m just thinking boxing.”

Facebook Twitter Pinterest The Diriyah Arena will host the first heavyweight title bout in the Middle East. Photograph: Richard Heathcote/Getty Images

“There are clues to success and you have to go back to what it takes to be a great heavyweight champion. We had to bring in hard, rough sparring partners. I brought in the toughest and roughest.”

Only three times in the 127-year history of the world heavyweight title has a champion regained the belt in a direct rematch, from the 10 fighters who have attempted it. The most recent was Lennox Lewis, who swatted away Hasim Rahman in Las Vegas in 2001. The other two were Floyd Patterson and Muhammad Ali, which gives you an idea of the elite company that Joshua hopes he will soon be in.

“I’m doing the same thing as Lennox,” he says. “It shows character because a lot of people would be like: ‘Nah, take your time, don’t rush it,’ but I don’t think I need any warm-up fights. I’m more than ready.”

Ruiz Jr disputes that, believing his opponent still carries the mental scars of being put down four times in their first meeting. He is an immensely likeable man who talks passionately about wanting to help build youth programmes to keep underprivileged children out of trouble. But when he steps into the ring his politeness and paunch are camouflage. If he can sustain the fire and intensity for 12 rounds he could spring another surprise but his shape raises serious questions.

Joshua is hoping to make history by winning the first world heavyweight title bout in the Middle East. The fight has drawn comparisons with Muhammad Ali and George Foreman's Rumble in the Jungle in Zaire in 1974.

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And in his tacit praise for the Saudi government he is at least walking a timeworn path. In the days before Ali’s victory he warmly embraced the Zaire’s dictator Mobutu Sese Seko and said he felt free in the country – the same Mobutu who was infamous for having the rebel Pierre Mulele’s eyes gouged out, his genitals ripped off, and his limbs amputated one by one, all while he was still alive.

There was no talk of sportswashing then. Rather Mobutu was seen as a curiosity, someone who, as the New York Times writer JJ Grimond noted, liked being “greeted as a saviour by squads of gyrating dancers swinging and stamping, waving and winnowing, and all the time singing the president’s praises”.

Perhaps Joshua will take comfort from the fact Ali’s reputation was only enhanced by what he did when he felled the mighty Foreman with a chopping right hand.

He also knows better than most that defeat will be disastrous for his reputation and ranking. “It will definitely be catastrophic if I lose but I’m not even thinking about that,” he says. “It will be big business when I win.”

But with £60m heading to his bank account on Saturday night, business – however grubby it may seem to some – is looking peachy enough already.