World Rugby has welcomed a new study examining changes in body mass of men’s and women’s international rugby players and the potential impact of law and shape of the game changes on player size. 

Published by the British Medical Journal and authored by Professor Ross Tucker with expert input from international coaches Stuart Lancaster, Gary Street and Phil Davies, the study tracks trends across Rugby World Cups and will help inform World Rugby’s evidence-based injury-prevention strategies. 

Overall, the study determined a stabilisation of mass for men’s international players since 2011 after a period of increase in the early professional era, while slightly smaller increases have been observed for women’s international players. 

Key findings include:

  • Since RWC 2011, there have been no significant increases in player mass
  • RWC 2019 was the first tournament since 1991 where neither forwards nor backs were heavier than in the previous tournament. Indeed, backs were slightly lighter in 2019 than in 2015
  • The proportion of very heavy players (identified relative to a comparison weight in 1991) has also decreased in 2019, while the proportion of lighter players (again defined as being lighter than a comparison value from 1991) increased in 2019
  • In women’s rugby, similar trends have been observed, though the more recent rapid growth of the women’s game means that women’s rugby is in its early phases of professional development. Consequently:
    • Mass of typical forwards has increased by 4.8 per cent between 2010 and 2017, while backs have shown no increase in size between the same period
    • Large differences were found between rugby's established and emerging nations with respect to changes, as emerging nations have shown little to no increase in mass, while established nation players have become significantly heavier since 2010
    • Future research tracking the evolution of female player size as the sport becomes more professional may reveal whether game demands have already set limits for women’s player mass
  • Initial increases were driven by factors including professionalisation of the sport, the growth of academies that develop players from a younger age, advances in conditioning methods, and changes in the demands of the game that are created by law changes and tactical evolution and approaches by coaches
  • The decrease in the rate of growth, and the potential plateau that has now been reached are also surmised to be the result of the game demands that have counteracted these changes. These include:
    • Law change that has increased ball in play time, which requires more mobile, endurance-oriented players
    • Law change that has increased the length of typical activity cycles, further necessitating that players be able to withstand fatigue, rather than those who can be conditioned to produce power for very short periods
    • Coaching intent, which has evolved to prioritise speed, mobility and playing tempo, both in attack and defence
The body mass of men’s players has stabilised after initial increases following professionalisation Ross Tucker , Stuart Lancaster, Phil Davies, Gary Street, Lindsay Starling, Cian de Coning, James Brown

Read the full study here

With law amendment and law application guidelines having possible impact on the shape of the game, including an increase in ball in play time and a reduction in scrum forces, there has been a shift towards a functional fitness requirement. World Rugby has delivered a number of resources to support those requirements, including the World Rugby Strength & Conditioning programme

Lead author Professor Ross Tucker said: “This study is unique because it marries together data analysed by researchers, but also the expert input of elite level coaches to interpret the findings. Stuart Lancaster, the Leinster and former England coach, was one of three coaches who contributed insights to the paper. Others were Phil Davies, who coached Namibia at the Rugby World Cup 2015 and 2019, and Gary Street, the victorious England women’s coach at Rugby World Cup 2014.
“The importance of player size has been recognised in various contexts – performance and player welfare. With World Rugby and its unions continually evaluating player welfare led law changes that have possible implications for player size, the research, combined with the coaches’ insights, will play a key role in informing future discussions."
World Rugby Chief Medical Officer Dr Éanna Falvey added: “Rugby does not stand still when it comes to player welfare and at the heart of our decision-making is research and evidence. This study and its unique insights will play an important role in informing decisions that further injury-prevention strategies in the game.
“While player size is sometimes perceived as a casual factor in injury rates at the elite level of the game, the study suggests that the upper limit of body mass is near or has been reached. It is, of course, important to acknowledge that the body composition of players may be changing, along with increased speed and power, but an assessment of size and mass alone suggests recent law changes may be contributing factors in counteracting size increases.”