A game for all shapes and sizes? Changes in anthropometric and performance measures of elite professional rugby union players 1999-2018.

Background: Rugby union player size has increased since the game turned professional in 1995. Changes in physical and performance capability over this period have yet to be fully described. Hypothesis: Increases in player momentum would result from changes in body mass. Methods: Within-player rates of change in anthropometric and kinetic variables with season played were sampled in three successively studied professional rugby union club cohorts playing at the highest level of European competition between 1999 and 2019. Data comprised 910 seasons of observation for 291 elite male players. Most players had 2, 3 or 4 seasons of observation. Mixed-effects modelling distinguished changes independent of position played, club and international status. Results: With each season played, player body mass, fat-free mass and maximum speed increased significantly, while per cent fat decreased. The mean maximal velocity of a rugby player in 1999 was 8.2 (±0.18) m/s, which in 2019 had risen to 9.1 (±0.10) m/s. Player's momentum in 2019 was 14% more than those playing in 1999. In the Front Five, momentum increased in this period by >25%, mainly driven by greater running speed, disproving our hypothesis. Conclusions: The momentum of players, particularly forwards, increased markedly over 20 seasons of professional rugby. The resulting forces generated in collisions are thus significantly greater, although these may be mitigated by better player conditioning. Proactive regulation to address player safety may be required to address the changing nature of anthropometric measures and physical performance, minimising injury rates and potential long-term sequelae.