FIFA 11+ Warm-Up and Injury Risk Classification in Youth Amateur Soccer Players

Background. Lower extremity injuries are a major burden in youth soccer. Isolated screening tools such as the Functional Movement Screen (FMS) and the Lower Quarter Y-Balance Test (YBT-LQ) have shown limited standalone predictive accuracy, whereas multifactorial classification frameworks may better identify at-risk athletes. The FIFA 11+ program is an established neuromuscular warm-up shown to reduce injury incidence, but its combined application with multifactorial risk classification has been studied mainly in collegiate and elite cohorts, leaving youth amateur players underrepresented.

Design. Parallel-group, single-blinded randomized controlled trial. Outcome assessments were performed at baseline and after eight weeks. All testing took place on the natural grass field where the athletes regularly trained, under standard training conditions. The study was conducted in accordance with the principles of the Declaration of Helsinki.

Randomization and blinding. After baseline assessment, participants were allocated 1:1 using computer-generated block randomization with a block size of four. The allocation sequence was prepared by an independent researcher not involved in data collection or analysis, and assignments were concealed from the recruiting investigator until after baseline testing. Investigators administering the FMS, YBT-LQ, jump tests, and strength assessments at both time points were blinded to group allocation. Participants and the supervising physiotherapist could not be blinded due to the nature of the intervention. Data were de-identified prior to statistical analysis.

Intervention. The experimental group performed the complete FIFA 11+ program three times per week for eight weeks before regular training, each session lasting approximately 20 minutes, supervised throughout by a certified physiotherapist who monitored technical execution, progressed exercise difficulty when criteria were met, and provided real-time correction to ensure intervention fidelity. The control group continued its routine pre-training warm-up over the same period.

Sample size. An a priori power analysis (G*Power 3.1; F-test, repeated measures within-between interaction) indicated a minimum total sample of 34 participants to detect a moderate effect (f = 0.25) for the Group x Time interaction with alpha = 0.05 and power = 0.80. Forty-four participants were enrolled.

Statistical analysis. A mixed-design (2x2) ANOVA assessed Group x Time interactions. Within-group changes were examined with paired t-tests following confirmation of normality using the Shapiro-Wilk test. Effect sizes were reported as Cohen's d and partial eta-squared. Bonferroni correction was applied to post hoc comparisons. Between-group injury incidence was compared using Fisher's exact test, with relative risk and 95% confidence intervals reported. Significance was set at p < 0.05.

Registration note. This trial was registered retrospectively.