Mental fatigue independent of boredom and sleepiness does not impact self-paced physical or cognitive performance in normoxia or hypoxia

Purpose: This study aimed to explore the individual and combined effects of mental fatigue (MF) and hypoxia (HYP) on physical and cognitive performance. Methods: Fifteen healthy males (24 ± 3 years) completed one familiarisation session and six experimental trials, including: 1) normoxia (0.209 FiO2) and no MF; 2) normoxia (0.209 FiO2) with MF; 3) mild normobaric HYP (0.13 FiO2) and no MF; 4) mild normobaric HYP (0.13 FiO2) with MF; 5) severe normobaric HYP (0.10 FiO2) and no MF; 6) severe normobaric HYP (0.10 FiO2) with MF. Each condition included a 15-min self-paced time trial on an arm bike, followed by a 60-s isometric maximal voluntary contraction (MVC) of the biceps brachii. Supramaximal nerve stimulation quantified central and peripheral fatigue. MF was induced using a 16-min individualised TloadDback cognitive test prior to exercise performance. Following each time trial, participants performed the Tower of Hanoi (TOH) cognitive test. Subjective measures of mental fatigue (VASF) and mood (BRUMS) were assessed. Results: A main effect of HYP was observed on average power output, oxygen consumption and muscle oxygenation (P ≤ 0.004), with no effect of MF (P ≥ 0.599). Voluntary activation of the biceps brachii was also reduced in HYP (68.42 ± 5.64%, P = 0.039). Time to completion in the TOH was increased in all conditions (+14.74 ± 6.99-s, P ≤ 0.041), however no effect of MF or HYP was observed on cognitive performance (P ≥ 0.138). Conclusion: HYP impacted physical performance, whilst MF had no effect on self-paced physical or cognitive performance.