Cognitive fatigue due to exercise under normobaric hypoxia is related to hypoxemia during exercise.

We previously found that a 10-min bout of moderate-intensity exercise (50% maximal oxygen uptake) under normobaric and hypoxic conditions (fraction of inspired oxygen [[Formula: see text]] = 0.135) reduced executive performance and neural activity in the left dorsolateral prefrontal cortex (DLPFC). To examine whether this cognitive fatigue is due to a decrease in SpO during exercise, we compared executive performance and related prefrontal activation between two experimental conditions, in which the participants inhaled normobaric hypoxic gas ([Formula: see text]= 0.135) (hypoxic exercise [HE]) or hypoxic gas adjusted so that SpO during exercise remained at the resting level (milder hypoxic exercise [ME]). ME condition showed that reaction time in executive performance decreased (t[13] = 2.228, P < 0.05, d = 0.34, paired t-test) and left DLPFC activity increased (t[13] = -2.376, P < 0.05, d = 0.63, paired t-test) after exercise compared with HE condition. These results showed that the HE-induced reductions in the left DLPFC activity and executive performance were both suppressed in the ME condition, supporting the hypothesis that exercise-induced cognitive fatigue under hypoxic environment is due to hypoxemia during exercise. This may lead to the development of a method of coping with cognitive fatigue due to exercise that causes hypoxemia.