Reliability, Validity, and Clinical Interrelationships of Lower-Extremity Screening Measures in College Athletes

Background/Objectives: Modifiable intrinsic factors such as foot posture, hallux mobility, dynamic balance, and body mass index (BMI) are widely assessed in athletic screening, but their reliability and interrelationships remain unclear. The aim of the study was to evaluate the reliability of foot posture, hallux mobility, dynamic balance, Q-angle, and navicular drop measures in collegiate athletes and to examine the relationships among these measures and BMI. The concurrent, discriminant, and predictive validity of the Foot Posture Index (FPI6) relative to the navicular drop test (NDT) was also assessed. Methods: Fifty-nine athletes participated: 10 in a reliability subsample and 49 in a separate validity subsample. Assessments included BMI, FPI-6, hallux valgus angle, hallux dorsiflexion, Y Balance Test (YBT), Q-angle, and NDT. Reliability was assessed using intraclass correlation coefficients (ICCs). Associations among measures and FPI6-NDT concurrent validity were examined using Spearman correlations and non-parametric group comparisons. Classification performance indices relative to NDT were calculated for FPI-6. Results: All measures demonstrated good to excellent reliability (ICC = 0.81-0.99). FPI-6 showed a strong concurrent association with NDT (rho = 0.735). More pronated foot posture was moderately associated with lower YBT performance and reduced hallux dorsiflexion (rho = -0.301 to -0.635). Higher BMI was associated with greater navicular drop and lower dynamic balance (rho = 0.301 to -0.433). FPI-6 showed high classification agreement with NDT-defined foot posture groups (specificity 96.9%; overall agreement 91.8%). Conclusions: Lower extremity alignment, hallux mobility, dynamic balance, and BMI showed modest interrelationships. FPI-6 demonstrated strong concurrent validity and high classification agreement relative to NDT, supporting practical screening use. Given the correlational nature of the findings, interpretations should remain cautious, and larger multimodal studies are warranted.