The Effect of Mental Fatigue on the Cerebral Oxygenation During Endurance Exercise

The investigators use a randomized, blinded, placebo controlled, counter-balanced, cross-over design. The real purpose of the study will be hold back from the participants by recruiting participants who are unaware of the possible negative effects of mental fatigue. We will inform the participants in a way that explains the study as an investigation about the influence of different cognitive tasks on a subsequent cycling. the investigators will strive equal expectations for all the participants in both the experimental and the control trial concerning the influence of the cognitive task on the cognitive and cycling task. At the end of the last trial the investigators will ask a standardized question to follow up on their thoughts about the objective of the study.

The experiment will consist of 3 consecutive trials performed in a sound-insulated climate chamber (20°C and 40% RH) at the VUB. Participants will be asked to return 3 successive weeks. Trained staff (pre-doctoral researchers and trained master students) will be present during the experimental trials. During the first visit, subjects will read and sign the informed consent and get a thorough explanation of what is expected from them, afterwards they will have the possibility to ask questions. After signing, participants complete a familiarization trial in which they will complete all procedures as if it was an experimental trial, except for the 60min cognitive task. Instead of the 60-min cognitive task the participants' maximal cognitive capacity will be determined. Therefore, a Stroop task divided in blocks of 96 stimuli will be used. After each block, the accuracy (ACC) will be calculated. When the ACC is higher than 85%, the difficulty of the Stroop task will be increased by decreasing the stimulus presentation time (SPT). If the ACC is lower than 85%, this block will be considered as an 'error' and the subject must re-do the block without changing the SPT. The first block will have a SPT of 1500 ms and will have the main objective to get familiar with the task. When the required accuracy is achieved, the SPT will decrease in the following order: 1100, 900, 800, 700, 650, 600, 550 ms... to determine the individual cognitive load. Before the start of each block, the subjects will be able to take a break if they like. When the subject makes three errors in a row, or five errors during the whole trial, the trial is considered as completed and will be ended. The SPT of the last, successfully completed block will be considered as the maximum capacity of that individual and will be used to individualize the difficulty of the 60-min Stroop task. There will be a continuous feedback of the performance to motivate the subjects, as this has been pointed out by Kurzban et al. to be important for task-engagement.

The next two trials will be performed in a counterbalanced randomized order, a mental fatigue trial (MF) and a control trial (CON). Randomization will be assured by using a web-based computer program (www.randomization.com) to determine treatment order (MF or CON trial; see intervention for details). All trials will be separated by at least 5 days to ensure full recovery.

After arrival at the laboratory for the experimental trials, participants will be asked to go to the toilet, after which they enter the climatic chamber which has reached 20°C and 40%RH. Participants will have to fill in 2 questionnaires (~3min) to estimate mood and motivation. NIRS equipment will be applied. The NIRS-optode pair will be applied prefrontally. NIRS measurement will start to verify hemodynamic changes during the absorption period. Physiological measures (HR, SaO2, BP, Hb, Respiratory Rate (RR), Glucose, NIRS, ventilation (VE), Blood lactate (BL) will be recorded.

Go/NoGo. As a manipulation check, the Go/NoGo paradigm task will be used to assess cognitive performance as suggested by Guo et al. (2018) and Kato et al. (2009). Participants are to react to different stimuli displayed on a computer screen positioned about 1 meter from the subject, preceded by a screen with general instructions. Two different stimuli were present at the same time: a Go or NoGo stimulus, and a left or right stimulus (meaning that four combinations are possible: GoRight, GoLeft, NoGoRight and NoGoLeft). If a Go-stimulus is presented, participants are instructed to react to the left or right stimuli with the corresponding arrows. However, if a NoGo stimulus is presented, participants are instructed to refrain from reacting to the either the left or right stimuli. This proposed paradigm measures attention, response inhibition and working memory, executive functions who are all consistently negatively impacted by MF. Stimuli will be presented for 500 ms, with a varying interstimulus time between 1100 and 1700 ms. Outcomes for Go trials include reaction time and accuracy while the outcome for NoGo trials is only accuracy. The ratio of Go/NoGo trials will be 80 to 20% respectively. Since the trials concern seven different interstimulus times, 1 cycle of trials consists of 56 Go and 14 NoGo trials. Moreover, to consistently detect large ERP's, research has suggested that between 30 and 40 stimuli should be present. Therefore, to be able to investigate ERP's in NoGo trials, at least 3 cycles are necessary to complete, leading to a tot task duration of about 6,5 min (taken into account a mean trial duration of 1900 ms).