Abstract
PurposeEndurance exercise in hypoxia promotes carbohydrate (CHO) metabolism. However, detailed CHO metabolism remains unclear. The purpose of this study was to evaluate the effects of endurance exercise in moderate hypoxia on exogenous glucose oxidation at the same energy expenditure or relative exercise intensity.MethodsNine active healthy males completed three trials on different days, consisting of 30 min of running at each exercise intensity: (a) exercise at 65% of normoxic maximal oxygen uptake in normoxia [NOR, fraction of inspired oxygen (FiO2) = 20.9%, 10.6 ± 0.3 km/h], (b) exercise at the same relative exercise intensity with NOR in hypoxia (HYPR, FiO2 = 14.5%, 9.4 ± 0.3 km/h), and (c) exercise at the same absolute exercise intensity with NOR in hypoxia (HYPA, FiO2 = 14.5%, 10.6 ± 0.3 km/h). The subjects consumed 113C‐labeled glucose immediately before exercise, and expired gas samples were collected during exercise to determine 13C‐excretion (calculated by 13CO2/12CO2).ResultsThe exercise‐induced increase in blood lactate was significantly augmented in the HYPA than in the NOR and HYPR (p = .001). HYPA involved a significantly higher respiratory exchange ratio (RER) during exercise compared with the other two trials (p < .0001). In contrast, exogenous glucose oxidation (13C‐excretion) during exercise was significantly lower in the HYPA than in the NOR (p = .03). No significant differences were observed in blood lactate elevation, RER, or exogenous glucose oxidation between NOR and HYPR.ConclusionEndurance exercise in moderate hypoxia caused a greater exercise‐induced blood lactate elevation and RER compared with the running exercise at same absolute exercise intensity in normoxia. However, exogenous glucose oxidation (13C‐excretion) during exercise was attenuated compared with the same exercise in normoxia.
Highlights
The use of exercise training in normobaric hypoxia has been widely accepted as a potent tool for improving endurance capacity in athletes, and a large amount of experimental evidence supports the efficacy of this training method (Czuba et al, 2011, 2017; Dufour et al, 2006)
We hypothesized that endurance exercise in hypoxia would augment 13C-excretion during exercise compared with the same exercise in normoxia, but that this difference would disappear when exercise intensity was relatively matched between normoxia and hypoxia
These differences disappeared when exercise intensity was relatively matched between normoxia and hypoxia
Summary
The use of exercise training in normobaric hypoxia has been widely accepted as a potent tool for improving endurance capacity in athletes, and a large amount of experimental evidence supports the efficacy of this training method (Czuba et al, 2011, 2017; Dufour et al, 2006). Previous studies (Katayama et al, 2010; Lecoultre, Boss, et al, 2010; Morishima et al, 2014; Sumi, Kojima, & Goto, 2018; Sumi, Kojima, Kasai, et al, 2018) have evaluated CHO metabolism during endurance exercise in hypoxia using several parameters including the respiratory exchange ratio (RER) and whole-body substrate oxidation. CHO metabolism evaluated by RER, blood lactate, and whole-body substrate oxidation was enhanced in hypoxia (Katayama et al, 2010; Lecoultre, Boss, et al, 2010; Morishima et al, 2014; Sumi, Kojima, & Goto, 2018; Sumi, Kojima, Kasai, et al, 2018). We hypothesized that endurance exercise in hypoxia would augment 13C-excretion (exogenous glucose oxidation) during exercise compared with the same exercise in normoxia, but that this difference would disappear when exercise intensity was relatively matched between normoxia and hypoxia
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