Electrocortical and Hemodynamic Changes within the Brain during Incremental Bicycle Exercise in Normoxia and Hypoxia: A Combined EEG/NIRS Study

The correlation of NIRS (near-infrared spectroscopy) and EEG (electro-cortical activity) in exercise studies has never been shown. Eight sport students performed an incremental bicycle exercise test under normoxic and hypoxic (12.7% O2) conditions respectively. EEG and NIRS recordings of the prefrontal cortex (PFC, Brodmann area 10. 46) were performed synchronously to shed light on their correlation. ANOVA revealed a higher absolute workload (231.3 ± 37.2 W), and relative PFC oxygenation under normoxic conditions, whereas hypoxic conditions resulted in earlier exhaustion (200 ± 26.7 W) and reduced PFC oxygenation. NIRS parameters increased remarkably with exercise intensity (P < 0.001) and differed between conditions (O2Hb: P < 0.001; HHb: P = 0.023; tHb: P = 0.016) and hemispheres (O2Hb: P = 0.023). For EEG, higher prefrontal cortical current density during compared to pre and post exercise was revealed for both conditions (P < 0.001). No difference between conditions and hemispheres were found. In conclusion, brain cortical activity is not impaired by hypoxia. No correlation between NIRS and EEG, but a moderate correlation between EEG and cardio-vascular parameters and a moderate to high correlation between NIRS and cardio-vascular parameters were found. The results emphasize that the transfer of EEG and NIRS results need to be done with caution.