Rugby fans who say the modern game is being dominated more and more by heftier players and pumped iron can now point to scientific evidence to back their case.
Teams with the tallest backs and heaviest forwards are the likeliest to win the World Cup, according to a study by French researchers published on Tuesday.
Adrien Sedeaud of the Institute of Sports Biomedicine and Epidemiology in Paris collected data for the age, weight and height for 2,692 players who took part in World Cup matches between 1987 and 2007, and compared this with their team's performance.
The players were divided into 1,457 forwards and 1,235 backs.
Throughout the 20-year period under study, the weight of all players progressively increased by more than 6.6 kilos. In height, forwards were 0.6 centimetres taller over 20 years, and backs 1.09 cms.
But the difference was startling among the teams that reached the quarters, semis and finals.
On average, forwards and backs among these high-performing sides were some two kilos heavier than the other teams.
Their backs were taller by around two centimetres, although there was little height difference among forwards.
Bigger did not mean fatter, though. A more intense training regime and rigorous nutritional regime led to more muscle, for speed and strength, over the two decades.
The change to bigness began with the advent of professionalism in 1995, which created a more high-intensity sport with more rucks, mauls and tackles per game among its forwards, says the paper.
Yet the more mobile game has also required greater endurance and speed among its backs, it says.
"The maximisation of builds and the quest for 'supersizes' are inherent to international-level rugby as in other sports," it says.
The 2011 World Cup, which is not covered in the study, had a final with two teams that were almost identical in terms of pack weight.
France's forwards weighed 903 kilos, and New Zealand's 902 kilos. New Zealand edged France by a single point, 8-7.
Even so, size is not everything.
Winning teams also had more collective experience among their forwards, determined as the percentage of players who had played in previous World Cups. In teams who hoisted the trophy, this was nearly 40 percent, compared with under 32 percent for other teams.
"Collective experience of forwards gives a clear advantage during phases of collective combat," says the paper, published in the British Journal of Sports Medicine. "The art of working together, sharing the action either on offence or defence, is the essence of rugby."
Only four teams - New Zealand, Australia, South Africa and England - have ever won the global trophy, an elite group that indicates that there are intangible factors in success, says Sedeaud.
"Winning teams in a Rugby World Cup may also owe their victory to their nation's economic, historical, political and technological investment in this sport."
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