Developing Clinically Relevant Cut-Off Values for Trunk Muscle Size in Relation to Lower Limb Injuries in AFL Players.

OBJECTIVE: To investigate the relationship between trunk muscle morphology and lower limb injury risk in elite Australian Football League (AFL) players and to explore clinically interpretable cut-off values for injury risk stratification. DESIGN: Prospective cohort study. METHOD: Participants included 43 athletes from one professional AFL team (mean age 23.9 years, height 190 cm, mass 90.2 kg). Preseason ultrasound imaging was used to assess trunk muscle size and function, including cross-sectional area (CSA) of the lumbar multifidus and quadratus lumborum (QL) and thickness of the transversus abdominis (TrA) and internal oblique (IO). Players were monitored over a full playing season for lower limb injuries resulting in games missed. Group comparisons and unadjusted logistic regression analyses were performed. Receiver operating characteristic (ROC) analyses were used to explore potential cut-off values. RESULTS: Smaller multifidus CSA (L5 average < 8.17 cm2; OR 10.0 [2.2-45.2]; p < 0.01) and larger QL CSA (average > 8.44 cm2; OR 7.3 [1.8-29.8]; p < 0.01) were associated with increased odds of lower limb injury. Trunk muscle thickness and contraction measures were not associated with lower limb or soft tissue injuries (all p > 0.05), with small and inconsistent effect sizes. CONCLUSION: Trunk muscle morphology is associated with lower limb injury risk in elite AFL players. These findings provide preliminary, clinically interpretable cut-off values that may assist in identifying athletes at increased risk; however, these thresholds require validation in larger cohorts. Trunk muscle assessment may support injury-risk screening and guide targeted physiotherapy interventions in applied high-performance settings.