Effect of carbohydrate ingestion on central fatigue during prolonged running exercise in moderate hypoxia.

To determine if acute exposure to moderate hypoxia alters central and peripheral fatigue, and to test whether carbohydrate ingestion impacts fatigue characteristics, 12 trained runners completed 3 running trials lasting 1 h each at 65% of normoxic V̇O2 max. The first trial was performed in normoxia (FI O2 = 0.21) and the last two trials were completed in hypoxia (FI O2 = 0.15). Participants ingested a placebo drink in normoxia (NORM-PLA), a placebo drink in hypoxia (HYP-PLA), or a carbohydrate solution in hypoxia (HYP-CHO). HYP conditions were randomized. Peripheral (ΔQtw,pot ) and central (ΔVA) fatigue were assessed via pre- to post-exercise changes in magnetically evoked quadriceps twitch. In HYP, blood was drawn to determine the ratio of free-tryptophan (f-TRP) to branched-chain amino acids (BCAA). Following exercise, peripheral fatigue was reduced to a similar degree between normoxia and hypoxia (ΔQtw,pot = -4.5 ± 1.3% and -4.0 ± 1.5% in NORM-PLA and HYP-PLA, respectively; P = 0.61). Central fatigue was present following normoxic and hypoxic exercise, but to a greater degree in HYP-PLA compared to NORM-PLA (ΔVA: -4.7 ± 0.9% vs. -1.9 ± 0.7%, respectively; P < 0.01). Carbohydrate ingestion did not influence central fatigue (ΔVA in HYP-CHO: -5.7 ± 1.2%; P = 0.51 vs. HYP-PLA). Following exercise, no differences were observed in the ratio of f-TRP to BCAA between HYP-PLA and HYP-CHO ( P = 0.67). Central fatigue increased during prolonged running exercise in moderate hypoxia despite the ratio of f-TRP to BCAA remaining unchanged. Ingesting carbohydrates while running in hypoxia did not influence fatigue development.