Over the past few decades Australian Rugby Union and Rugby League players have been getting progressively heavier. Contributing factors have included an increased emphasis on heavy weight training, the use of dietary supplements and the high proportion of Pacific Islanders in teams of both codes. Nevertheless there remains a clear tendency for professional Union players to be heavier than League players as the following table illustrates:
Comparative Bodyweight of Australian Professional Rugby Union and Rugby League Forwards and Backs
Av Weight (kg) - Forwards
Av Weight (kg) - Backs
Australian Wallabies - Squad
NSW Waratahs - Squad
ACT Brumbies - Squad
Manly Sea Eagles – Grand Final Team
Melbourne Storm – Grand Final Team
Like Soccer and Australian Football, Rugby League is a continuous-flow type game, whereas Rugby Union is characterised by frequent stoppages with a significant time lapse before play restarts. Thus Union players require a lower level of aerobic fitness. Not surprisingly then, Union players whether backs or forwards tend to be heavier than their League counterparts.
The table indicates that the difference between the body weights of professional Union and League backs is not particularly great, whereas it is much more substantial in the case of forwards. One reason for this is the need for tall, heavy lineout forwards in Union, who are often around 200cm in height with corresponding body mass. With their high centre of gravity, such players are generally unsuited for Rugby League.
But the main reason for the weight disparity relates to the fundamentally different dynamics of the modern forms of each code. As I pointed out in a 2006 article, "Rugby - the most strength-oriented code of football":
"Rugby players spend considerably more playing time in physical contact and contest with opponents than players in other forms of football.
"Much of this contact involves extended grappling and wrestling, but what is also characteristic of rugby is the amount of time spent attempting to drive forward under loads considerably heavier than bodyweight. Obviously this is so in the scrum and maul, but also at the tackle. Both ball-carrier and tackler may strive to drive one another backward for an extended time after engagement. American football and rugby league are also primarily collision sports, but their tackles tend to terminate much more quickly."
There is an obvious advantage in having greater body mass where the sport requires extended physical engagement, although this may have a cost in terms of reduced mobility. Thus it can be confidently anticipated that Union forwards will always tend to be heavier than League forwards.
Those who advocate or foresee a merging of the two codes of Rugby fail to comprehend the fundamentally different physical demands placed on forwards in Union and League.