Sit-to-Stand Navicular Drop Test-Based Injury Risk Zones Derived from a U-Shaped Relationship in Male University Athletes.

Background/Objectives: Foot mobility is considered an intrinsic risk factor for lower-limb injury, yet commonly used pronated/neutral/supinated classifications rely on arbitrary cut-points. This study aimed to develop a data-driven framework for characterizing a continuous SSNDT-injury risk gradient and deriving clinically interpretable relative-risk bands that define practical injury risk zones along the sit-to-stand navicular drop test (SSNDT) continuum. Methods: Data from 137 physically active male students (274 feet) were analyzed. Intra-rater reliability of the sit-to-stand navicular drop test (SSNDT) was assessed using ICC(3,1). A quadratic mixed-effects logistic regression model was used to characterize the SSNDT-injury relationship and derive odds-ratio-based risk bands for interpretive and screening purposes. Results: SSNDT demonstrated good intra-rater reliability (ICC(3,1) = 0.82). Model comparison supported a non-linear, U-shaped association between SSNDT and injury risk, with a minimum risk value at approximately 5.5 mm. Bootstrap analysis supported a smooth continuous risk gradient. Four representative OR levels (1.2, 1.5, 1.8, and 2.0) were selected to define SSNDT-based interpretative risk bands. Injury prevalence showed an overall increasing trend across these zones, ranging from 4.2% in the Safe zone to 52.4% in the Extreme zone. Conclusions: SSNDT provides a robust, data-driven basis for quantifying foot-mobility-related injury risk along a continuous non-linear gradient and for deriving clinically interpretable relative-risk bands grounded in a validated model. The proposed framework avoids arbitrary cut-points and supports individualized risk screening.