## 4 Discussion
Another notable finding in our study was the behavior of the EEG/VO\({}_{2}\) ratio, which remained stable throughout most of the exercise but increased slightly around 80% of the test duration in both the alpha and beta bands. This increase, which was more pronounced in the IET, indicates a tendency towards heightened neural engagement relative to physiological demand as exercise intensity peaked. This suggests that the brain was allocating more resources to manage the escalating strain. The more pronounced rise in the IET may indicate that this protocol required greater cognitive and motor effort, potentially contributing to earlier fatigue compared to the SPV test. In contrast, the stable EEG/VO\({}_{2}\) ratio in the SPV test suggests better exertion management, thus maintaining neural efficiency and delaying central fatigue. This pattern of neural engagement aligns with the concept of the Estimated Time Limit (ETL), which posits that individuals subconsciously regulate their effort based on an internal estimate of how long they can sustain a given intensity before reaching exhaustion [50; 51]. As exercise progresses, the brain continually reassesses this internal time limit, adjusting neural and physical effort to prevent premature fatigue. The stabilization of the EEG/VO\({}_{2}\) ratio around 80% of the test duration across both protocols suggests that participants may have been tapping into this internal pacing strategy as they approached their perceived time limit. This regulatory mechanism is thought to involve both physiological signals, such as cardiovascular and metabolic feedback, as well as psychological factors, including motivation and perceived exertion, as suggested by previous research [10; 52]. Although we did not directly assess psychological factors in this study, the observed increase in neural engagement towards the end of the exercise could reflect the brain's efforts to marshal additional resources to extend performance as participants reared their ETL, thereby delaying the onset of central fatigue and maintaining overall effort. These findings regarding the EEG/VO\({}_{2}\) ratio contrast with those of [PERSON] et al. (2024), who observed a significant decline in the EEG/VO\({}_{2}\) ratio during the IET, suggesting reduced neural engagement [53]. The divergence in results could be attributed to several factors. First, while both studies employed an IET, [PERSON]'s study used 2 min stage durations, whereas our protocol used 3 min stages. Research suggests that shorter stages, like those used by [PERSON], may lead to quicker attainment of peak values but may not allow sufficient time for physiological stabilization, particularly for VO\({}_{2}\)max and other physiological parameters. In contrast, the longer stages in our protocol likely promoted more stable physiological responses, which could explain the variation in the EEG/VO\({}_{2}\) ratio between the two studies [54; 55]. Additionally, our IET protocol included alternating eyes open and eyes closed phases between increments, potentially introducing brief moments of neural recovery that were absent in [PERSON]'s continuous protocol. These differences in stage duration and protocol design may account for the distinct neural and physiological responses observed in our study. Furthermore, the strictly controlled incremental protocol employed by [PERSON] might have imposed a higher cognitive load and led to more pronounced central fatigue earlier in the exercise [10]. Moreover, the populations studied could also contribute to the differences in results. [PERSON]'s study included active males who participated in a variety of sports, such as judo and water polo, and not exclusively endurance sports. The diversity in training backgrounds certainly would have influenced their physiological responses and how they engaged neural resources during exercise. In contrast, our study involved trained cyclists, which might explain the more stable neural engagement observed in our participants.