The Rugby World Cup has never been bigger – and nor have its huge players

As the Rugby World Cup begins, it's clear the game's stars are super-sizing. But how does that affect their play – and who else is in the running?

The prize for the most unintentionally ironic name of anyone taking part in the 2015 Rugby World Cup goes to French prop forward Uini Atonio. This formidable hulk of man answers to "Weeny" but stands 197cm tall, and at 155kg is the second heaviest player ever to play international rugby. As England prepare to take on Fiji this evening in the opening game of the tournament, much of the talk centres around Fiji's Nemani Nadolo, the 130kg "demolition man" who has predicted a "jaw-dropping" performance from his hefty side. But in this tournament, gargantuan is par for the course. Uini Atonio is closely followed on the scales by Australian Will Skelton and Samoan Census Johnston at 140kg and 138kg respectively, while Ireland's Devin Toner and Wales's Luke Charteris tower more than 10cm over "Weeny". The 620 players in this year's tournament average over 6ft in height, and would have sides from the last World Cup in 2011 seeking urgent advice on how to bulk up. Even an armchair fan like me can see that rugby is changing; these men are larger, heavier, fitter and, crucially, faster. As one 2001 study into international rugby teams concluded: "There's a close association between body size and success" – and that's not just true for rugby. In many sports, bigger has become better.

"You have to admire the physique, the power, stamina and strength of the modern day player," says Ed Morrison, who refereed the 1995 Rugby World Cup Final in Johannesburg. "They work incredibly hard to achieve that – and as a result it's a completely different sport. The level of training at the top end has turned these men into complete athletes, and they're so much bigger than the former players." There are many stats and studies to back this up. A comparison undertaken by the BBC of British rugby players between 1962 and 2012 showed that their average weight increased from 85.7kg to 104kg, and the weight is still piling on; in 2012 England's forwards averaged 112.9kg, while today that figure tips 114kg. Forwards have always been hefty, of course, but there are few players in this tournament who you'd want to see running headlong at you with a ball under their arm. "If you look across the pitch," says Morrison, "you can see that everyone is huge."

Size has become critical in many sports. The height and weight of tennis Grand Slam champions, both male and female, has risen over the decades, with their "wingspan" widening and the power of their serve intensifying. Swimmers have seen a similar growth spurt, improving their leverage and acceleration through the water. The effect on rugby, as noted by Morrison, has been profound; it has become incredibly contact-heavy, with high-speed collisions and dug-in positions leading, some would say, to an attritional game that's far from beautiful. But audiences love it; however much rugby purists may wipe away at tear at the sight of nifty wingers running rings around huge forwards and leaving them face down the mud, there's an evident hunger for the spectacle of enormous human specimens locked in fierce combat.

In some sports, such as cycling or cricket, size is advantageous but can, at some point, start to become a drawback. Former Croatian tennis player (now coach) Ivan Ljubicic reckons that male tennis players have an optimum size of around 6ft 5in. "You can make the most of the height," he said in interview in 2013, "without giving up too much in the other areas." But while there are ways of asserting your power without having height and weight on your side, being faced with a larger opponent takes some getting over, according to Paul Russell, a chartered psychologist with a particular interest in sport. "If you're transfixed on their size," he says, "you become very problem focused. You focus on the fact that he's bigger than you – 'Oh God, he's still bigger than me!' – and that multiplies and snowballs. I work with athletes on detaching themselves from that and becoming more solution focused, playing to your strengths in order to nullify theirs."

In some sports, such as sumo wrestling, brute force is paramount and there's seemingly no upper limit to weight; American amateur Emmanuel Yarborough is the current Guinness World Record holder for heaviest living athlete, weighing in at 319kg at his peak – although he's since slimmed down to more dainty 270kg. In other sports, most notably football, height and weight seems to offer no particular advantage; according to one study, 95% of the world's population would fall into the body type distribution of great footballers – and according to another, height could even prove to be a disadvantage, as taller players are statistically more likely to be blamed for fouls.

The spectacle of physical collision between players has a darker side, particularly in super-sized modern rugby; while there have always been smacks on the head, injuries have increased and early retirements are rising. But this is not a sport that can somehow be de-powered or divided into weight classes; it has become survival of the largest. "For me," sighs Ed Morrison, "one of the principles of rugby was that it was a game for all shapes and sizes. But," he continues excitedly, "there's a player called Matthew Morgan in the Welsh squad who's probably 11 stone soaking wet – and what a wonderful player. When he gets the ball, I lift myself off my seat. He can do things that people can only dream about – and it's amazing, in a way, in terms of his physique and his size, that he's survived this far." The statistics may show that rugby is a game for man-mountains – but maybe size isn't everything. µ

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incredible hulks five men not to mess with

Alexander Karelin

Considered the greatest Greco-Roman wrestler of all time, his extraordinary strength led to various nicknames including 'Russian Bear', 'Russian King Kong', and 'The Experiment'. It's not surprising the 6ft 4in retiree weighed in at 290lbs considering he was a 12lb baby. Never mind his opponents – his poor mother.

Eric Esch

Bearing an uncanny resemblance to the fibrous legume, it's not hard to see why Esch was given his nickname, 'Butterbean'. At a pretty average 5ft 11in, the American heavyweight boxer makes up for impact with his weight: all 425lbs of it. No wonder he managed to knock out 58 of his 89 opponents during his career.

William Perry

It was Perry's diet that really made him a superstar (and gave him his nickname 'The Refrigerator'). He claimed to eat eight cheeseburgers, six portions of chips, and six shakes – just for lunch. The 335lb Chicago Bears lineman was the proud owner of the largest NFL Championship ring that's ever been produced.

John Daly

While American Daly would almost be considered trim by his country's standards, on the golf course his 276lb figure was quite unique. Known for his chaotic personal life, the 1995 Open champion gambled away £39m and had four failed marriages. He has since had a gastric band fitted and given up the booze.

Dwayne Leverock

At the 2007 Cricket World Cup, 280lb Leverock was the largest player in the tournament. When the Bermudian bowler claimed two of England's best batsmen – Paul Collingwood and Kevin Pietersen – in successive overs, he gained a huge following and it led to headlines such as "Big trouble from little Bermuda".

GILLIAN ORR