Purpose: This study aimed to (1) evaluate the acute metabolic, mechanical, and perceptual responses to curve versus linear repeated-sprint-training (RST) protocols in highly trained youth soccer players and (2) analyze whether the sprint trajectory influences the time course of recovery following RST protocols. Methods: Twenty-seven highly trained youth soccer players randomly performed 2 RST protocols (12 × 17 m with 15-s intervals) with different trajectories: linear or curve (radius of 9.15 m). Blood lactate concentration, countermovement-jump height, modified reactive strength index, and myotonometric measurements of the biceps femoris long head (stiffness, frequency, and decrement) were assessed before and 0 minutes, 5 minutes, and 24 hours after the protocols. Likewise, best and average sprint velocities were recorded in both protocols, and perceptual responses were evaluated using Borg and Hooper scales. Results: Linear RST showed higher velocity outputs than curve RST (P < .001). No significant time × condition interactions were observed for blood lactate concentration, countermovement-jump height, modified reactive strength index, time to takeoff, or myotonometric measurements (all P < .05), except for right-leg stiffness (P = .047), which significantly increased from 0 minutes to 24 hours only after curve RST (P < .05). Additionally, players also reported poorer sleep quality (P = .045) following the curve RST. Conclusions: Overall, these findings suggest that the acute metabolic, mechanical, and perceptual demands of RST are not trajectory dependent. Therefore, strength and conditioning coaches can use both trajectories to address soccer-specific sprint demands in elite youth soccer players.
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