Differences between playing positions and age categories in body composition and physical performance of Portuguese youth rugby players: An analysis of the Bronco test, CMJ, and 40-m sprint

Abstract

Physical performance in youth rugby reflects the interaction of maturation, playing position and body composition. We analysed 285 assessments from 222 male youth rugby players collected across two seasons (2024: n = 113; 2025: n = 172), spanning U15–U17 and classified as backs or forwards. Players completed anthropometry and body-composition assessment (InBody 270), countermovement jump (CMJ), squat jump (SJ), CMJ with free arms, T-test, 40-m sprint and the Bronco test (total time, s). Two-way ANOVA (Type III) was run separately for 2024 (2×2: age × position) and 2025 (3×2), and linear mixed-effects models were applied to the longitudinal subsample (63 players assessed in both seasons). Position was the most robust factor: forwards were consistently slower than backs in the Bronco in both seasons; the age-grade effect was significant in 2025 and only a non-significant trend in 2024, with no age × position interaction. In adjusted models, body fat mass (BFM) was the strongest independent predictor of Bronco time, whereas CMJ and fat-free mass (FFM) were non-significant after adjustment. Longitudinally, CMJ improved significantly while fat mass tended to increase. These findings reinforce the relevance of body-composition optimisation and position-specific conditioning across youth age grades.