Passive and active exercise do not mitigate mental fatigue during a sustained vigilance task

Executive function (EF) is improved following a single bout of exercise and impaired when an individual experiences mental fatigue (MF). These performance outcomes have been linked to a bi-directional change in cerebral blood flow (CBF). Here, we sought to determine whether MF-induced by a sustained vigilance task (i.e., psychomotor vigilance task: PVT) is mitigated when preceded by a single bout of exercise. Participants completed 20-min single bouts of active exercise (cycle ergometry involving volitional muscle activation), passive exercise (cycle ergometry involving a mechanical flywheel) and a non-exercise control intervention. EF was assessed pre- and post-intervention via the antisaccade task. Following each intervention, a 20-min PVT was completed to induce and assess MF, and transcranial Doppler ultrasound of middle cerebral artery velocity (MCAv) was used to estimate intervention- and PVT-based changes in CBF. Active and passive exercise provided a post-intervention reduction in antisaccade reaction times; that is, exercise benefitted EF. Notably, however, frequentist and Bayesian statistics indicated the EF benefit did not mitigate MF during the PVT. As well, although exercise (active and passive) and the PVT respectively increased and decreased CBF, these changes were not correlated with behavioral measures of EF or MF. Accordingly, a postexercise EF benefit does not mitigate MF during a sustained vigilance task and a bi-directional change in CBF does not serve as a primary mechanism associated with EF and MF changes. Such results provide a framework for future work to explore how different exercise types, intensities and durations may impact MF.