A comparison of substrate oxidation during prolonged exercise in men at terrestrial altitude and normobaric normoxia following the coingestion of 13C glucose and 13C fructose

John O'Hara, David Woods, Adrian Mellor, Christopher Boos, Liam Gallagher, Costas Tsakirides, Nicola Arjomandkhah, David Holdsworth, Carlton Cooke, Douglas J. Morrison, Thomas Preston, Roderick King

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    Abstract

    This study compared the effects of coingesting glucose and fructose on exogenous and endogenous substrate oxidation during prolonged exercise at altitude and sea level, in men. Seven male British military personnel completed two bouts of cycling at the same relative workload (55% Wmax) for 120 min on acute exposure to altitude (3375 m) and at sea level (~113 m). In each trial, participants ingested 1.2 gmin1 of glucose (enriched with 13C glucose) and 0.6 gmin1 of fructose (enriched with 13C fructose) directly before and every 15 min during exercise. Indirect calorimetry and isotope ratio mass spectrometry were used to calculate fat oxidation, total and exogenous carbohydrate oxidation, plasma glucose oxidation, and endogenous glucose oxidation derived from liver and muscle glycogen. Total carbohydrate oxidation during the exercise period was lower at altitude (157.7 56.3 g) than sea level (286.5 56.2 g, P = 0.006, ES = 2.28), whereas fat oxidation was higher at altitude (75.5 26.8 g) than sea level (42.5 21.3 g, P = 0.024, ES = 1.23). Peak exogenous carbohydrate oxidation was lower at altitude (1.13 0.2 gmin1) than sea level (1.42 0.16 gmin1, P = 0.034, ES = 1.33). There were no differences in rates, or absolute and relative contributions of plasma or liver glucose oxidation between conditions during the second hour of exercise. However, absolute and relative contributions of muscle glycogen during the second hour were lower at altitude (29.3 28.9 g, 16.6 15.2%) than sea level (78.7 5.2 g (P = 0.008, ES = 1.71), 37.7 13.0% (P = 0.016, ES = 1.45). Acute exposure to altitude reduces the reliance on muscle glycogen and increases fat oxidation during prolonged cycling in men compared with sea level.
    Original languageEnglish
    Article numbere13101
    JournalPhysiological Reports
    Volume5
    Issue number1
    DOIs
    Publication statusPublished - 13 Jan 2017

    Keywords

    • Altitude
    • Carbon isotope
    • exogenous carbohydrate oxidation
    • liver glycogen
    • muscle glycogen
    • plasma glucose oxidation

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