Does cerebral oxygen delivery limit incremental exercise performance

ous studies have suggested that a reduction in cerebral oxygen delivery may limit motor drive, particularly in hypoxic conditions, where oxygen transport is impaired. We hypothesized that raising end-tidal PCO2 (PETCO2) during incremental exercise would increase cerebral blood flow (CBF) and oxygen delivery, thereby improving peak power output (Wpeak). Amateur cyclists performed two ramped exercise tests (25 W/min) in a counterbalanced order to compare the normal, poikilocapnic response against a clamped condition, in which PETCO2 was held at 50 Torr throughout exercise. Tests were performed in normoxia (barometric pressure 630 mmHg, 1,650 m) and hypoxia (barometric pressure 425 mmHg, 4,875 m) in a hypobaric chamber. An additional trial in hypoxia investigated effects of clamp-ing at a lower PETCO2 (40 Torr) from 75 to 100 % Wpeak to reduce potential influences of respiratory acidosis and muscle fatigue im-posed by clamping PETCO2 at 50 Torr. Metabolic gases, ventilation