## 2 Materials and Methods
### Experimental Design  
Participants were seated in a chair. Using an abrasive cream (Nuprep(r), Weaver and Company, Aurora, CO, USA) and a cotton swab, the skin was rubbed at the location of the reference and ground electrodes. This operation removed dead cells, impurities, and excess sebum to improve conductivity. Additionally, the forehead, scalp, and hair were degreased with a compress soaked in 70% alcohol [52]. They were then fitted with a Polar(r) heart rate belt, a gas mask, and an EEG headset. The EEG electrodes were positioned with conductive gel between the scalp and the electrodes to improve contact between the skin and the sensor. Subjects were then seated in a semi-recumbent position on a cyclo-ergometer, as shown in Figure 2.  
Figure 1: Summary of experimental session. The session began with a brief EEG calibration, followed by an 8 min warm-up. After a 5 min recovery period, the IET was performed until exhaustion. RPE test was then performed during the next 5 min of recovery, before the final EEG calibration procedure. EEG: electroencephalogram, IET: incremental exercise test, and RPE: rate of perceived exertion.  
In accordance with traditional recommendations [53; 54], the electrodermal sensors were placed on the second phalanx of the second and third fingers of the non-dominant hand (or on the third phalanx, in case of frequent potential contact between the sensors and the environment). A conductive gel (Teca, ref. 822-201210) was applied between the sensors and the skin to improve contact after cleansing the skin with a mixture of alcohol and ether. The electrodes were then firmly strapped to the fingers using hypoallergenic adhesive tape. Finally, six 3D kinematic markers were placed on the head and shoulder (see Figure 2).  
The impedance of the EEG electrodes was then checked, allowing the conductive EEG gel time to warm up to body temperature. The target impedance values were between 1 and 5 k\(\Omega\). If the impedance values were higher than 5 k\(\Omega\), conductive gel was added until the impedance reached the required values. At this point, the EEG calibration procedure began, as shown in Figure 3, and proceeded in the following sequence: 30 s with eyes open, 30 s with eyes closed, 15 s of eye blink, 15 s of eye movement, and 12.5 s of head movement alone in the four directions (left, right, up, and down). A 7.5 s pause was observed between each test sequence. The experimental EEG calibration procedure was carried out using Presentation(r) software (version 18.1, www.neurobs.com (accessed on 19 June 2024)) and presented on a computer in front of the subject. Participants were asked to look straight ahead and to remain motionless during the procedure, except for what they were asked to do.  
Figure 2: Positioning of sensors and participants on the ergocycle.  
After remaining static during the EEG calibration sequence, each participant warmed up for 8 min (see Figure 1). They were then fitted with a nafion/permapure sampling tube connected to a turbine for measurements of pulmonary gas exchange. Each subject then performed the physical test described above. The participants were asked to remain seated on the saddle in order to limit head and upper body movements as much as possible. After each test and one minute's rest, each participant was asked to complete a perceived exertion rating scale (see below). After a 5 min rest, the EEG calibration procedure (Figure 3) was again performed, along with the impedance check.  
Rating of Perceived Exertion (RPE) Scale  
We asked each participant to rate the perceived exertion on a scale of 6 to 20 at the end of the IET. A score of 6 corresponds to rest and is closely correlated to a resting heart rate value, while 20/20 corresponds to maximal effort with the highest heart rate values [55].