## 4 Discussion  
The main aim of this study was to compare the EEG responses during an incremental exercise test in two groups of subjects who had achieved a VO2 pl or not. The debate around the VO2 pl and its cause remains a long story of exercise physiology for nearly half a century, and as [PERSON] [59] states, \"it is time to move beyond a brainless exercise physiology\". We hypothesize that the difference between athletes who reached the plateau of their VO2 max and those who did not could be present in different EEG characteristics and in EEG/VO2 ratios. Our main results showed no incidence of the VO2 pl or not, nor of endurance or non-endurance practice, on EEG activity during IET. Regardless of group, all subjects showed an increase in beta and theta band power, while alpha band power was less uniform (half increasing and half decreasing, independent of group membership). However, when we plotted the EEG band power against oxygen power demand, both relative to the start value, all subjects showed a decrease in alpha, beta, and theta/VO2 ratios during IET. Therefore, even if the brain is not the limiting factor of VO2 max or responsible for the attainment of VO2 pl or not, these results, given the relationship between EEG responses and oxygen demand, could constitute a new marker of a progressive \"depletion\" of EEG power capacity. Considering each of these elements, it may be recalled that at rest, alpha waves are generally more observed when a person is in a relaxed mental state [60]. During exercise, an increase in alpha activity may indicate increased attention or alertness, as the brain focuses on the task at hand [61]. However, an excessive reduction in alpha activity during exercise may reflect a large effort, yielding mental fatigue or decrease cognitive performance [62]. Beta waves are associated with active concentration, problem solving, and alertness [63]. During exercise, increased beta wave activity may reflect heightened cognitive engagement and concentration, particularly during tasks requiring attention and coordination [64; 65]. Theta waves are linked to deep relaxation, meditation, and drowsiness [66]. During exercise, a decrease in theta \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Positive Alpha Tendency** & **Negative Alpha Tendency** & \(p\) **Value** \\ \hline NONEND & 12 & 10 & 0.07 \\ END & 15 & 5 & 0.07 \\ \hline NOPLAT & 14 & 6 & \\ PLAT & 12 & 10 & 0.75 \\ \hline NONEND: non-endurance group, END: endurance group, NOPLAT: non-plateau group, and PLAT: plateau group. & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Frequency distribution of alpha value trend in subjects. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Cadence** & **EEG 0/\(\hat{\text{VO}}_{\text{2}}\)** & **EEG \(\alpha\)/\(\hat{\text{VO}}_{\text{2}}\)** & **EEG \(\beta\)/\(\hat{\text{VO}}_{\text{2}}\)** & \(\alpha\)/\(\beta\) **Ratio** & **All** \\ \hline Chi-square & 0.005 & 0.225 & 0.431 & 0.558 & 0.288 & 7.61 \\ (Observed value) & 3.84 & 3.85 & 3.86 & 3.84 & 3.87 & 16.9 \\ (Critical value) & 0.945 & 0.636 & 0.512 & 0.455 & 0.591 & 0.57 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Chi-square test for cadence, EEG \(\beta\)/\(\hat{\text{VO}}_{\text{2}}\), EEG \(\theta\)/\(\hat{\text{VO}}_{\text{2}}\), EEG \(\alpha\)/\(\hat{\text{VO}}_{\text{2}}\) and \(\alpha\)/\(\beta\) ratio between the NONPLAT (\(n\) = 22) and PLAT (\(n\) = 20) groups. wave activity can occur when a person is overexerted, which can lead to difficulties in maintaining precise sensorimotor control and monitoring sensory inputs due to reduced executive functions or decreased attention [67]. Overall, beyond EEG changes in the alpha, beta, and theta bands during exercise, the increases observed relative to that of VO2 highlight the importance of including central measures in our physical activity studies. This was the goal of this interdisciplinary approach using physiology, neurophysiology and biomechanics synchronizing all measurements during exercise performed at free cadence.