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

Abstract

To determine whether acute exposure to moderate hypoxia alters central and peripheral fatigue and to test whether carbohydrate ingestion impacts fatigue characteristics, 12 trained runners completed three running trials lasting 1 h each at 65% of normoxic maximum oxygen uptake. The first trial was performed in normoxia [inspired O2 fraction (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 [change in potentiated quadriceps twitch force (Qtw,pot)] and central [change in voluntary activation (VA)] fatigue were assessed via preexercise-to-postexercise 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). After exercise, peripheral fatigue was reduced to a similar degree in normoxia and hypoxia (Qtw,pot 4.5 1.3% and 4.0 1.5% in NORM-PLA and HYP-PLA, respectively; P 0.61). Central fatigue was present after normoxic and hypoxic exercise but to a greater degree in HYP-PLA compared with NORM-PLA (VA: 4.7 0.9% vs. 1.9 0.7%; P 0.01). Carbohydrate ingestion did not influence central fatigue (VA in HYP-CHO: 5.7 1.2%; P 0.51 vs. HYP-PLA). After 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 although the ratio of f-TRP to BCAA remained unchanged. Ingesting carbohydrates while running in hypoxia did not influence fatigue development.