Frontal cerebral cortex blood flow, oxygen delivery and oxygenation during normoxic and hypoxic exercise in athletes

Non‐technical summary  Exercise capacity is limited at high altitude where hypoxia (i.e. decreased amount of inspired oxygen resulting in decreased oxygen in the blood) is present, but it is unknown whether a reduction in the oxygen delivered to the brain constitutes the signal to the brain to prematurely terminate exercise. We show that during hypoxic exercise equivalent to exercise at ∼4000 m above sea‐level, the oxygen delivered to the brain during intense exercise is ∼60% less than that delivered to the brain at comparable exercise intensity at sea‐level. These results show that reduction in the oxygen delivered to the brain could constitute the signal to limit maximal exercise capacity in hypoxia, and help us understand better why exercise capacity is limited at high altitude. Moreover, a plausible mechanism of exercise limitation in patients who present decreased oxygen in the blood during exercise due to pulmonary and/or cardiac disease is revealed.