New research published in the British Medical Journal has found that after a significant increase since professionalism, the average bodyweight of men rugby players is beginning to stabilise.

The study, led by Ross Tucker, assessed the mass of international rugby players in men’s and women’s Rugby World Cups between 1991 and 2019. The objective was to quantify changes in mass of players by position. 4,447 elite male and 958 elite female players from both tier 1 and tier 2 nations participated in the sample.

‘Increases in body mass … are of interest for both player welfare and performance reasons. Given the frequency of contact events in rugby, the contribution made by body mass to inertia, momentum and kinetic energy to injury risk means that collisions involving larger players, or where mismatches occur, may increase injury risk.’

The study found that men’s player mass increased significantly between 1991 and 2019 (9.7% in tier 1 nations) but that this increase ‘occurred almost entirely up to 2011’. It was observed that forwards and backs were not significantly heavier at the 2015 RWC than the 2007 or 2011 events.

‘At some point, however, increasing body mass may compromise acceleration, speed, agility and endurance, becoming detrimental to performance … player body mass may be approaching a plateau beyond which no further performance advantages occur.’

The paper hypothesised the causes of the plateau. It suggests that recent law changes introduced to increase ball-in-play time have reduced the amount of rest time available to players and has changed conditioning paradigms to favour lighter players. Changes in playing styles and coaching intent to embrace more ‘running’ rugby and ‘rush’ defence patterns have also had an impact.

The research also showed significant disparities in body mass between tier 1 and tier 2 nations and posited that this may be one factor in explaining the performance gap over time.

‘Size confers advantages on larger players since it enables greater absolute force production and may improve players’ ability to “win” collisions. Advantages gained in the tackles and rucks may improve ball-retention ability.’

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