Exogenous glucose oxidation during endurance exercise in hypoxia

Abstract

Purpose: Endurance 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.

Methods: Nine 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 (F_i O₂ ) = 20.9%, 10.6 ± 0.3 km/h], (b) exercise at the same relative exercise intensity with NOR in hypoxia (HYPR, F_i O₂ = 14.5%, 9.4 ± 0.3 km/h), and (c) exercise at the same absolute exercise intensity with NOR in hypoxia (HYPA, F_i O₂ = 14.5%, 10.6 ± 0.3 km/h). The subjects consumed ¹¹³ C-labeled glucose immediately before exercise, and expired gas samples were collected during exercise to determine ¹³ C-excretion (calculated by ¹³ CO₂ /¹² CO₂ ).

Results: The 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 (¹³ C-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.

Conclusion: Endurance 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 (¹³ C-excretion) during exercise was attenuated compared with the same exercise in normoxia.

Keywords: endurance exercise; exogenous glucose oxidation; hypoxia; lactate.