This study aimed to evaluate the biomechanics of single-leg drop landing in individuals with functional ankle instability (FAI) during cognitive tasks, contrasting these findings with those of healthy controls to provide insights for evidence-based rehabilitation strategies. Fifteen FAI participants, identified using clinical tools, were age- and activity-matched with controls. They performed drop landings with and without a cognitive task, and the data were analyzed using a 2 × 2 mixed ANOVA. At the initial ground contact (IC), the FAI group’s affected side showed a significantly smaller plantarflexion angle than the control group (p = 0.008). With cognitive tasks, this angle increased in the FAI group (p = 0.005). The FAI group also had larger knee flexion at contact (p = 0.002) and greater knee valgus at peak vertical ground reaction force (vGRF) (p = 0.027). They exhibited a higher peak vGRF, shorter time to peak vGRF (T-vGRF), and higher loading rate (LR) (all p < 0.05). No differences were found in other variables (p > 0.05). This study shows that FAI individuals make specific biomechanical adjustments under cognitive tasks, notably increased plantarflexion at IC, suggesting reactive compensations. Despite similar motor control to controls, this may reflect long-term adaptations rather than equal proficiency.

(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.