Trends in body mass between finalist teams in the Japanese collegiate rugby union championship: a 15-year analysis

This study examined the relationship between body mass and match outcomes among university rugby players in a Japanese collegiate rugby union championship over a 15-year period (2008-2022). Using data from 680 players across 30 finalist teams, we analyzed trends in body mass by playing position and their impact on match outcomes. No interaction was observed for body mass in matches over 15 years for all registered players (interaction [year × match], <i>p</i> = 0.85). Although no significant annual increase in body mass was observed across the period, the winning teams consistently had heavier players, with an average difference of 2.2 kg. The forwards of the winning teams were, on average, 3.6 kg heavier, and their reserve players for forward positions were 4.2 kg heavier than those of the losing teams. These findings emphasize that body mass is a crucial factor in determining success at university level, particularly in forward positions. This study highlights the need for further investigation of the role of body composition, physical assessments, and game-related factors to better understand the determinants of rugby performance.