Effects of Combined Nordic Hamstring and Speed Deceleration Training on Measures of Physical Fitness in Male Youth Soccer Players

<b>Background:</b> A high level of physical fitness is a critical factor for optimal soccer performance. Therefore, developing key physical components such as sprinting, jumping, and change of direction (CoD) abilities from an early age is essential for both short- and long-term athletic success. While previous research in adolescent male athletes has demonstrated improvements in physical fitness following eccentric training, the effects of such training during the pubertal stage remain unclear. This study examined how an eccentric training program, combining the Nordic hamstring exercise with horizontal speed deceleration training, influenced physical fitness parameters in prepubertal soccer players. <b>Methods:</b> Thirty-six players were randomly divided into an ET group (n = 19) or an active control group (CG; n = 17). Both groups maintained their regular soccer training routines, with the ET group replacing 15 to 25 min of low-intensity drills with eccentric exercises twice per week for eight weeks. Pre- and post-intervention assessments included 20 m linear sprint speed, change of direction, agility, vertical jump, and standing long jump. <b>Results:</b> Significant group-by-time interactions were observed for all performance measures (<i>p</i> < 0.05), with moderate-to-large improvements in the ET group (<i>d</i> = 0.56 to 1.51; ∆3.83% to 14.95%) and no significant changes in the CG (<i>d</i> = 0.05 to 0.24; ∆0.38% to 1.31%). Individual response analysis indicated that 57 to 100% of players from the ET group and 23-58% from the CG group reached improvements beyond the smallest worthwhile change (SWC_0.2). <b>Conclusions:</b> Collectively, these findings support the inclusion of eccentric training interventions, such as the Nordic hamstring exercise and horizontal speed deceleration training, to enhance sprinting, jumping, directional changes, and agility in young soccer players.