The Impact of Different Footwear Conditions on Lower-Limb Biomechanical Characteristics During Single-Leg Drop Landing Movements in Individuals with Functional Ankle Instability

(1) Background: This study investigated the impact of different footwear conditions on the biomechanics of individuals with Functional Ankle Instability (FAI) during single-leg drop landing movements. (2) Methods: Fifteen participants with FAI and a control group were tested. Kinematics and kinetics were measured using Vicon (Model: MX13, Oxford, UK) and Kistler (Model: 9287B, Switzerland) equipment. A mixed-ANOVA analyzed the impact of footwear conditions. (3) Results: At the initial contact (IC), under the shoe-wearing condition, the FAI group exhibited a significantly smaller ankle-joint plantarflexion angle compared to the control group (p = 0.001). The FAI group exhibited a significantly smaller ankle-joint plantarflexion angle under the shoe-wearing condition compared to the barefoot condition at the IC (p < 0.001). At the IC moment, regardless of the footwear conditions in this study, the FAI group showed a larger knee flexion angle (p = 0.028) and a shorter time to vertical ground reaction force (T_vGRF) (p = 0.020) compared to the control group. (4) Conclusions: The study concluded that footwear conditions significantly influence the biomechanics of FAI individuals, with shoes enhancing ankle stability and barefoot conditions leading to biomechanics similar to healthy individuals. The effect of socks on FAI individuals was not significant. Future research should further explore the impact of footwear on FAI rehabilitation.