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.

This study investigated the impact of mental fatigue on lower limb biomechanics and bilateral asymmetry during drop landings in elite collegiate American football players to assess injury risk implications. Twelve elite male players performed bilateral drop landings before and after a 45-minute Stroop task. Data were analyzed using a 2 × 2 repeated-measures ANOVA. Irrespective of mental fatigue, the dominant limb exhibited significantly smaller hip flexion, larger peak vertical ground reaction force, and longer time to vertical ground reaction force peak compared to the non-dominant limb. Following mental fatigue, knee flexion range of motion and peak vertical ground reaction force increased bilaterally, and the non-dominant limb specifically demonstrated greater knee varus/valgus range of motion compared to baseline. While the symmetry index indicated baseline asymmetry, mental fatigue exerted no significant effect on global symmetry index. We conclude that mental fatigue impairs landing mechanics through limb-specific constraints rather than systemic symmetry collapse. Because localized compensatory mechanisms can preserve the overall symmetry index, relying solely on global symmetry metrics may mask underlying, joint-specific injury risks under mental fatigue. Consequently, athletic screening should prioritize the sensorimotor resilience of the non-dominant limb.

Objective: To investigate the kinetic performance, power decline trajectory, and lower limb load asymmetry characteristics during the push-off phase of a 30-repetition continuous vertical jump task in individuals with functional ankle instability (FAI), and to reveal potential motor control deviations under cyclic high-output conditions. Methods: Eleven males with unilateral FAI and eleven healthy control participants were recruited to complete a task consisting of 30 continuous double-leg vertical jumps. Kistler force plates and Visual3D software were utilized to extract relevant kinetic data and corresponding asymmetry indices. A linear mixed model (LMM) was constructed based on jump order to analyze kinetic trajectories. Furthermore, the rate of power decline was quantified via individual regression slopes and compared between groups. Results: (1) The FAI group exhibited significantly higher asymmetry in peak vertical ground reaction force (vGRF) ( p = 0.030). (2) While no significant Group × Jump Order interaction was observed for overall jump height or impulse ( p > 0.05), the FAI group presented a significantly flatter decline slope in peak vGRF compared to controls ( p = 0.046), indicating a distinct output strategy rather than a general performance failure. Conclusion: Although individuals with FAI are capable of maintaining overall power output levels comparable to healthy controls during cyclic high-output tasks, they exhibit an unbalanced load distribution and a “low amplitude–low decline” kinetic output mode. This reflects a compensatory motor control structure formed over the long term. Bilateral load asymmetry and the rhythm of output decline are more indicative of potential control deficits than overall performance metrics. Future assessment and rehabilitation should prioritize the restoration of strength, neuromuscular control, and kinetic balance on the affected side to improve dynamic stability under fatigue conditions and reduce the risk of re-injury.