Zhang Zhilei is no ordinary human being. Standing at 198 centimeters tall and weighing 130 kilograms, he isn't just bigger than most males on the planet, he's also taller and heavier than most other heavyweight boxers.

Genetics, of course, are largely responsible for his man-mountain frame, but to build a physique that can deliver punishing blows to his opponents - and absorb them - for 12 three-minute rounds requires a strict diet and training regime.

Zhang, who turned 40 in May, is preparing for a rematch with Britain's Joe Joyce at London's Wembley Arena on Saturday, as he looks to repeat his dominant technical knockout victory back in April.

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While in camp, Zhang must live a boxer's life. That means early nights, earlier mornings, multiple training sessions per day and a diet designed to help him to fuel and recover from bruising sessions. 

"Generally speaking, if I train in the morning, I get up at five o'clock in the morning," he said to CGTN. "If I get up at five o'clock in the morning, I might go to bed at eight or nine o'clock in the evening."

There are no cheat days to enjoy fast food or stay up late watching movies. "During camp I have one day off on a Sunday," he says. "If there is no fight coming up then I'll train Monday to Friday and have two days off at the weekend."

Nutrition is also key. While Zhang must consume enough calories to fuel his giant frame, his diet must be comprised of the right blend of protein, carbohydrates, healthy fats and vitamins and minerals to maximize his recovery and performance on fight night. The result is a body that maximizes the athletic potential of his frame which is at a career-heaviest 130 kg. 

"My breakfast is usually six boiled eggs, with a little oatmeal and eat some vegetables," he says. "For lunch, I eat some steak or salmon, then eat rice, add some boiled vegetables, and then eat some protein and carbohydrates at night. The only seasonings I eat are a little salt and pepper."

Father time has a habit of catching up with even the sport's most talented fighters. But advances in sports science and nutrition have helped some of boxing's biggest names to compete at the highest level until their late-30s and even into their 40s.

In recent times, Floyd Mayweather hung up his gloves at the age of 40. In the heavyweight division, a number of fighters have also continued to fight long after their supposed physical peak. George Foreman was 45 when he came out of retirement to win the world heavyweight title - he remains the oldest ever world champion in the sport.

But not all fighters are capable of keeping up with young and hungry fighters with fewer miles on the clock. Zhang turned 40 shortly after his win over Joyce and is confident he's at the peak of his powers after a career best win.

"I don't feel any different (than when I was 20)," he said. "To be an elite athlete your life must be regular and self disciplined. You have to think every day, 'what should I eat and drink and what time should I go to bed?' When you do this your body will remain in good condition."

On Saturday night, Zhang will hope his body powers him to another famous victory and a step closer to a shot at the world heavyweight title.

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