Characterising the plasma metabolome following high intensity interval exercise in continuous and intermittent hypoxia in overweight individuals

The aim of this work was to examine changes in the plasma metabolome in response to high‐intensity interval exercise (HIIE) performed under three distinct hypoxia protocols. On separate days, 18 inactive individuals with overweight completed a HIIE protocol in randomised conditions: normoxia (N Ex ‐N Rec ), normobaric hypoxia (inspired O 2 fraction ∼0.14) during both the work and recovery (H Ex ‐H Rec ), normobaric hypoxia during recovery only (N Ex ‐H Rec ) and normobaric hypoxia during work only (H Ex ‐N Rec ). Venous blood samples were collected before and after each HIIE for metabolite analyses by liquid chromatography–mass spectrometry and 1 H‐nuclear magnetic resonance spectroscopy. Mean power output, averaged across the six work bouts, was lower in H Ex ‐H Rec compared to N Ex ‐N Rec , N Ex ‐H Rec and H Ex ‐N Rec (all P ≤ 0.009), with no differences (all P ≥ 0.11) between the other conditions. Arterial oxygen saturation was lower in H Ex ‐H Rec compared to other conditions (all P < 0.001). Concentrations of pyruvate and closely associated metabolites (alanine, citrate, lactate) increased consistently across all conditions (all P < 0.001; Hedge's g : 0.43–1.73), without differences between conditions (all P > 0.37). The lactate to pyruvate ratio increased in all conditions, but did not differ between them. Free‐fatty acid (FFA) classes (saturated, monounsaturated and polyunsaturated FFAs) showed consistent increases (all P < 0.001), while monounsaturated and saturated triacylglycerol (TAG) classes significantly decreased following HIIE (both P < 0.04). There were no condition × time interaction effects for any metabolites. HIIE significantly altered the concentration of glycolytic and TCA cycle intermediates, whilst concomitantly increasing FFA and decreasing TAG concentrations. Although hypoxia applied either continuously throughout HIIE or intermittently (work or recovery) during HIIE altered exercise performance and oxygen saturation, it had limited additional effect on metabolite concentrations.