Unresisted Sprints Versus Heavy Resisted Sled Training: Relationships With Performance Indicators and Implications for Training Prescription in Elite Youth Rugby Players

Abstract

Zabaloy, S, Freitas, TT, G ´alvez-Gonz ´alez, J, Tondelli, E, Pereira, LA, and Loturco, I. Unresisted sprints versus heavy resisted sled training: relationships with performance indicators and implications for training prescription in elite youth rugby players. J Strength Cond Res 39(9): 989–995, 2025—The aim of this study was to analyze the associations between sprint velocities achieved under unresisted and resisted (50% body mass [BM]) sprint conditions, squat 1-repetition maximum (squat 1RM) and its associated strength deficit (SDef; from 40 to 90% squat 1RM), and horizontal and vertical jump performance in elite youth rugby players. Twenty-five under-19 youth male rugby players (n 5 25; age: 17.3 6 0.9 years) participated in this study and completed the following tests during the preparation period leading up to the 2024 in-season period: unresisted and resisted 30-m sprints, squat 1RM, countermovement jumps, and standing long jumps. Results showed that unresisted and resisted sprint velocities were significantly associated with both jump tasks (r: 0.46–0.76; p , 0.019), while relative squat 1RM measures (i.e., 1RM relative to BM) demonstrated stronger correlations, compared with absolute 1RM values, with sprint velocities under both conditions, as well as with vertical and horizontal jump metrics (r: 0.40–0.74; p , 0.045). SDefs across the entire range of loads (i.e., 40–90% squat 1RM) were also significantly associated (r: 0.84–0.99; p , 0.001). In summary, the present findings highlight the importance of considering relative strength as an additional measure of strength performance, particularly when the primary objective is to enhance a wide range of sport-specific capabilities. Finally, the associations observed among all values of SDef indicate that reducing this strength-derived variable, especially under lighter loading conditions, is highly constrained or even impossible.