Effects of Light Versus Very Heavy Resisted Sprint Training on Multidirectional Speed in Semi-professional Soccer Players.

Baena-Raya, A, Robles-Ruiz, J, Pérez-Castilla, A, Pareja-Blanco, F, and Rodríguez-Pérez, MA. Effects of light versus very heavy resisted sprint training on multidirectional speed in semi-professional soccer players. J Strength Cond Res 39(2): e155-e161, 2025-The purpose of this study was to evaluate the effects of an 8-week resisted linear sprint training (RST) program with 2 loading conditions (light vs. very heavy) on linear sprint (LS), curve sprint (CS), and change of direction (COD) performance in young soccer players. Thirty-eight male under-19 soccer players were assessed for 30-m LS, CS, and modified 505 COD tests. Players were randomly allocated into 3 groups: control ( n = 18), light ( n = 10), and very heavy RST ( n = 10). Light and very heavy RST groups performed RST with external loads resulting in a 25 and 75% velocity loss from the player's maximal LS velocity, respectively. The control group did not perform any sprint training. Significant group × time interactions were observed for LS, CS, and COD performances ( p < 0.05). The control group showed no performance improvement. Both RST groups showed significant improvements in LS at 10-, 20-, and 30-m ( p ≤ 0.03; effect size [ES] ≥ 0.62), whereas no significant changes were observed for the split times ( p > 0.05). CS performance was significantly increased by the 2 RST groups ( p ≤ 0.03; ES ≥ 0.60), except for light RST on CS right side at 17-m ( p = 0.09; ES = 0.46). Change of direction performance was only significantly enhanced by the very heavy RST group ( p ≤ 0.001; ES ≥ 0.80). No significant changes between RST groups were observed. In conclusion, using both light and very heavy RST can enhance LS and CS performance, whereas very heavy RST is recommended to optimize COD performance in young soccer players.