Comparison of Two Posterior Chain Strength Training Protocols on Performance and Injury Incidence in Elite Youth Football Players

<i>Background and Objectives</i>: This study compared the effects of two posterior-chain strength training strategies on eccentric hamstring strength, jump and sprint performance, and hamstring injury incidence in elite youth soccer players. <i>Materials and Methods</i>: Twenty-three players were randomly allocated to either a Nordic Hamstring Exercise Group (NHEG; <i>n</i> = 11) or a Deadlift + Leg Curl Slides Group (D + LCSG; <i>n</i> = 12). Both groups completed a 9-week in-season resistance training program consisting of one strength-oriented session (MD-4) and one power-oriented session (MD-2) per week, in addition to regular soccer training. Pre- and post-intervention assessments included eccentric hamstring strength (NordBord), countermovement jump (CMJ), and 10 m and 30 m linear sprint performance. <i>Results</i>: Eccentric hamstring strength increased significantly only in the NHEG (<i>p</i> ≤ 0.05), though this improvement did not transfer to enhancements in jump or sprint performance (<i>p</i> > 0.05). No significant changes were observed in the D + LCSG for any variable (<i>p</i> > 0.05), and no between-group differences were found across all performance outcomes. During the 12-week monitoring period, one hamstring injury was recorded, occurring in the NHEG. <i>Conclusions</i>: These findings suggest that, while the NHE elicited greater exercise-specific eccentric strength gains, neither posterior-chain strategy produced improvements in sprint or jump performance. However, given the small sample size and low number of injury events, these trends cannot be attributed with certainty to the implemented protocols, and both programs reported a low incidence of hamstring injuries per 1000 h of exposure with no statistically protective effect associated with the use of the NHE.