The purpose of this study was to investigate the associations of body composition, force and velocity on squat jump height and countermovement jump height in male sub-elite university rugby union players. Seventeen male sub-elite university rugby union players performed a countermovement jump (1kg) and squat jumps using ascending loads of 1kg, 20kg, 40kg and 60kg on one single testing session at the beginning of the season. Linear force-velocity associations and body composition using dual x-ray absorptiometry (DXA) were derived, and the following variables were acquired: total body less head (TBLH) lean mass (kg), legs lean mass (kg), TBLH body fat %, TBLH fat mass (kg), theoretical maximal force (N/kg) and theoretical maximal velocity (m•s-1). The players TBLH body fat % had a statistically significant correlation with the countermovement jump height 1kg (r= -0.723, p= 0.001), squat jump height 1kg (r= -0.608, p= 0.010), squat jump height 20kg (adjusted r2= 0.238, p= 0.027) and squat jump height 40kg (adjusted r2= 0.207, p= 0.038). TBLH fat mass also influenced the countermovement jump height 1kg (r= -0.736, p= <0.001), squat jump height 1kg (r= -0.683, p= -0.003), squat jump height 20kg (adjusted r2= 0.292, p= 0.015), squat jump height 40kg (adjusted r2= 0.212, p= 0.036) and theoretical maximal velocity (r= -0.503, p= 0.039). However, TBLH lean mass, leg lean mass, theoretical maximal force and theoretical maximal velocity had no statistically significant association on the countermovement jump or any of the squat jump loading conditions. This suggests that reducing the amount of TBLH fat mass and TBLH body fat % will improve jump performance, although having more overall mass and lean mass is not necessarily advantageous for improving jump performance. Therefore, the present study provides foundational data for future research to further investigate the associations between body composition, force, velocity and jump height in male rugby union players
