Position-Specific Differences in Physical Fitness Characteristics Among Adult Male Rugby Players—Systematic Review

Background: Rugby union and rugby league are among the most physically demanding contact team sports, in which playing positions impose distinct physical requirements. The aim of the review was to collect and synthesize available data on positional differences in physical fitness between forwards and backs in adult male rugby players. Methods: The systematic review was conducted in accordance with PRISMA 2020 and SWiM guidelines and was prospectively registered in the OSF database (10.17605/OSF.IO/E4Y37). Four electronic databases were searched: PubMed, SPORTDiscus, Web of Science, and Scopus up to June 2026. The search identified 3058 records, which were reduced to 1343 after language and document-type limits and then screened. Eligibility criteria were applied within the PICOs framework. Methodological quality was assessed using JBI Critical Appraisal Checklists and the AXIS tool as a validation instrument. Due to considerable methodological heterogeneity, narrative synthesis with directional meta-synthesis was applied. Results: Thirty-seven studies were included (n > 2000 players; 15 countries; 1996–2025). Forwards achieved higher values of absolute muscular strength and power, body mass, and sprint momentum, whereas backs performed better in sprint tests (10–50 m), maximum sprint velocity, aerobic fitness (VO2max, Yo-Yo IRTL1), CMJ height, and relative power. Following normalization to body mass, positional differences in strength and power were attenuated or reversed. In the only study that isolated the change in direction deficit, no clear positional difference was observed. Conclusions: Body mass appears to be the principal explanatory factor underlying positional differences in absolute strength and power. Position-specific fitness profiles are observable as early as the U20 category and become more pronounced with increasing competitive level. Strength and conditioning coaches should compare positional groups using body mass normalized ratio or, where justified, allometrically scaled measures rather than absolute values.