Endurance exercise performance in acute hypoxia is influenced by expiratory flow limitation

Purpose: We sought to determine if expiratory flow limitation influences intensive aerobic exercise performance in mild hypoxia. Methods: Fourteen trained male cyclists were separated into flow-limited (FL, n = 7) and non-FL (n = 7) groups based on the extent of expiratory flow limitation exhibited during maximal exercise in normoxia. Participants performed two self-paced 5-km cycling time trials, one in normoxic (F_IO₂ = 0.21) and one in mild hypoxic (F_IO₂ = 0.17) conditions in a randomized, balanced order with the subjects blinded to composition of the inspirate. Percent change from normoxia to hypoxia in average power output (%ΔP_TT) and time to completion (%ΔT_TT) were used to assess performance. Results: Hypoxia resulted in a significant decline in estimated arterial O₂ saturation and decrements in performance in both groups, although FL had a significantly smaller %ΔP_TT (−4.0 ± 0.5 vs. −9.0 ± 1.8 %) and %ΔT_TT (1.3 ± 0.3 vs. 3.7 ± 0.9 %) compared to non-FL. At the 5th km of the time trial, minute ventilation did not change from normoxia to hypoxia in FL (3.4 ± 3.1 %) or non-FL (2.3 ± 3.7 %), but only the non-FL reported a significantly increased dyspnea rating in hypoxia compared to normoxia (~9 %). Non-FL athletes did not utilize their ventilatory reserve to defend arterial oxygen saturation in hypoxia, which may have been due to an increased measure of dyspnea in the hypoxic trial. Conclusion: FL athletes experience less hypoxia-related aerobic exercise performance impairment as compared to non-FL athletes, despite having less ventilatory reserve.