Conference Paper

Liosis, L.-D., Martinez-Santos, R., & Santos-Concejero, J. (2026, April 15–16). Inter-individual variability in responses to the FIFA 11+ program for ACL injury prevention: A call for research [Paper presentation]. International Congress of Injury Prevention and Reconditioning of Football Injuries 2026, Vitoria-Gasteiz, Spain.

Authors

Loudovikos-Dimitrios Liossis, Raul Martinez-Santos & Jordan Santos-Concejero

Abstract

The FIFA 11+ program has been widely used as an injury prevention tool in youth and adult soccer players (Khan et al., 2025). It has been shown to reduce lower-limb injury risk associated with modifiable factors in soccer players of both sexes aged >13 years by approximately 30% (Sadigursky et al., 2017). More recently, the program has been reported to protect against anterior cruciate ligament (ACL) injury by improving movement biomechanics, including reductions in dynamic valgus angle and peak coronal knee abduction angle, as well as increases in knee flexion angle (Cierson et al., 2025; Mercurio et al., 2025). Despite its effectiveness, the FIFA 11+ program is primarily delivered in a standardized format and does not account for inter-individual variability in athlete responses. Although evidence supports its role in ACL injury prevention (Magaña-Ramírez et al., 2024), the optimal in-tensity and volume for individual athletes remain unclear, presenting a challenge for the development of personalized FIFA 11+-based strategies.

Given that physiological responses and adaptations to physical activity interventions vary between individuals, tailoring injury prevention programs is essential to maximize both efficiency and effectiveness (Gronwald et al., 2020). Accordingly, we encourage researchers to investigate the moderating effects of inter-individual variability on FIFA 11+ outcomes. Identifying non-responders may facilitate the development of more individualized ACL injury prevention strategies. Key metrics for assessing inter-individual variability should include knee coronal and sagittal plane angles measured during a standardized 30-cm drop jump test, together with the Landing Error Scoring System (LESS), as biomechanical proxies for ACL injury risk (Padhua et al., 2009; Cierson et al., 2025). Measurement reliability should be evaluated using intraclass correlation coefficients where appropriate. Statistical analyses should include paired-samples t-tests and effect size calculations to compare pre- and post-intervention values. The smallest worthwhile change should be applied to quantify inter-individual variability, classify athletes as responders or non-responders, and identify meaningful individual adaptations. Knee angle data should be classified according to established high-risk thresholds: initial coronal angle > 2.96°, peak coronal angle > 6.16°, and peak sagittal angle > 93.82° (Corban et al., 2023). LESS scores should be categorized as high risk (≥ 5 errors) or low risk (< 5 errors) (Hanzlíková & Hébert-Losier, 2025), enabling classification of athletes into injury risk categories and evaluation of changes following the intervention; landing distance should be standardized to 50% of the athlete’s body height in accordance with the original LESS protocol (Hanzlíková & Hébert-Losier, 2025). Ultimately, program design should emphasize individualization to optimize performance and minimize injury risk in competitive soccer.