## 4 Discussion  
This study examines the effects of a functional fatigue protocol and visual information on postural control in patients with CAI. Specifically, we investigate whether open versus closed eyes influence postural control differently in CAI patients following the induction of functional fatigue. To the best of our knowledge, this study is the first to investigate postural control and visual reliance in CAI patients under conditions of functional fatigue. The findings revealed that the blocking of visual input and the implementation of sports-specific fatigue protocols reduced the control of static posture among those with CAI. Specifically, this study demonstrated a negative impact of functional fatigue on the capacity for postural control among CAI patients when performing tasks with their eyes open, while no significant changes were observed after the fatigue protocol under conditions with the eyes closed. Moreover, the research highlighted a significant decrease in reliance on visual input, indicating that functional fatigue alters the sensory strategies used by individuals with CAI, causing them to rely less on visual information. Regardless of whether individuals were fatigued, a significant main effect of vision was observed. Individuals with CAI exhibited overall decreased TTB minima in eyes closed conditions compared with the case with their eyes open. These results align with previous findings [15; 42; 43; 44; 45; 46] indicating that, in CAI patients, postural deficits worsen in the absence of visual information. Chronic injuries of the ankle joints can lead to damaged sensory afferents, reducing available somatosensory feedback and diminishing the ability of the postural control system to generate effective corrections to maintain equilibrium during unilateral weight-bearing [47]. This observation could potentially highlight a factor contributing to the recurrent episodes of the ankle \"giving way\" during functional activities, as the CAI patients exhibited a diminished ability to regulate COP excursions concerning the ML and AP limits of stability. Figure 4: %Modulation changes between pre- and post-fatigue for time-to-boundary (TTB) minima mean and TTB minima standard deviation (SD) in the mediolateral (ML) and anteroposterior (AP) directions. Abbreviations: AP, anteroposterior; ML, mediolateral; SD, standard deviation; TTB time to boundary. * Indicates a statistically significantly difference between PRE and POST (\(p<0.05\)). ** Indicates a statistically significantly difference between PRE and POST (\(p<0.001\)). The results of this study regarding fatigue's main effect provide compelling evidence that fatigue significantly impairs static postural control in CAI patients, particularly when assessed with the visual assistance of open eyes. These findings are consistent with previous research indicating that CAI patients often experience a prolonged decrease in their ability to interpret sensory information from the somatosensory function, which includes the foot and ankle complex [15]. When CAI is compounded with functional fatigue, the reduction in somatosensory function may become more pronounced, exacerbating the challenges faced by affected individuals to maintain precise control over their movements. Ankle instability and fatigue are two factors confirmed to exert adverse effects on somatosensory function, specifically impacting the transmission and processing of sensory signals originating from the ankle joint and relaying them to the central nervous system. However, a key finding of this study was that CAI patients were unable to compensate for somatosensory deficits through visual feedback, even when they kept their eyes open under fatigued conditions. This is supported by the %modulation data obtained in this study, and a decrease in visual reliance was observed after fatigue. This can be explained by the SD of TTB minima, which indicates the consistency of TTB measurements and reflects the level of constraints on the sensorimotor system [48].