Incidence, severity, and burden of injury in the Japanese elite men's Rugby Union league.

OBJECTIVES: Japan Rugby League One comprises three divisions based on competitive level. We aimed to determine the incidence, severity, burden, and mechanism of match injuries in Japan Rugby League One and to examine the differences across divisions and between higher- and lower-ranked teams, for rankings defined within each division. DESIGN: Prospective cohort study. METHODS: The study conducted over four seasons (2022-2025) recruited male Rugby Union players from all Japan Rugby League One teams; time-loss injuries sustained during official matches were recorded. The injury incidence (injuries/1000 player-hours), mean severity (mean days lost), and burden (days/1000 player-hours) were calculated. Based on their final ranking within each division, teams were classified as higher-ranked or lower-ranked. RESULTS: Overall incidence, mean severity, and burden were 64.0 injuries/1000 player-hours (95% confidence interval: 61.1-67.0), 35 days, and 2235 days/1000 player-hours, respectively. Division 3 had a higher injury incidence (73.2 injuries/1000 player-hours; 95% confidence interval: 66.4-80.7) than Division 1 (incidence rate ratio = 1.23; 95% confidence interval: 1.09-1.38; p < .001). Concussion was the most frequent injury (12.0 injuries/1000 player-hours, 95% confidence interval: 10.8-13.4), whereas knee injuries imposed the greatest burden (592 days/1000 player-hours). Of all injuries, 54% were tackle-related. Lower-ranked teams experienced a higher injury incidence when facing higher-ranked teams (incidence rate ratio = 1.37; 95% confidence interval: 1.25-1.51; p < .001). CONCLUSIONS: Division-level disparities and ranking-related risk factors highlight the need for tailored prevention strategies; enhanced medical support for lower divisions; and interventions targeting concussions, knee injuries, and tackling techniques.