Effects of Sprint and Eccentric Hamstring Training in Elite Youth Soccer Players

This study will compare two different training methods used to improve sprint performance and hamstring strength in elite youth soccer players. Participants aged 16-17 years will be assigned to one of three groups: a sprint training group, an eccentric hamstring strength training group, or a control group. The two training programs will be performed for 6 weeks alongside the players' regular soccer and strength-conditioning training. The main purpose of the study is to determine whether sprint training or eccentric hamstring strength training is more effective for improving sprint speed and sprint mechanical performance. Sprint performance will be assessed over 5, 10, 20, and 30 meters, together with mechanical variables derived from sprint force-velocity profiling. Eccentric hamstring strength will also be measured before and after the intervention. The study will address whether a 6-week sprint training program can improve sprint performance and hamstring strength to a similar or greater extent than a targeted eccentric hamstring strength program. It is expected that sprint training will produce greater improvements in sprint-related performance, while eccentric hamstring training will produce greater improvements in eccentric hamstring strength.

Inclusion Criteria: \- Age 16-17 years and post-peak height velocity (post-PHV). Competing at the highest level of youth soccer in their country. Regular participation in soccer training (approximately 4 sessions per week, 90 minutes each) and competitive matches. Successful completion of the mandatory medical examination. At least 1 year of regular physical training, including sprint or resistance training within the club. Attendance of at least 80% of the intervention training sessions. Exclusion Criteria: * History of any lower-limb or trunk injury within 6 months before the pre-test. Sustaining a serious lower-limb or trunk injury during the experimental period. Regular participation in eccentric hamstring strength training or resisted sprint training during the 2 months before the pre-test measurements. Goalkeepers.will be automatically excluded from the study. Attendance below 80% of the intervention training sessions.