title: 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.
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 g·min-1of glucose (enriched with13C glucose) and 0.6 g·min-1of fructose (enriched with13C 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 g·min-1) than sea level (1.42 ± 0.16 g·min-1, 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.
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom J.OHara@leedsbeckett.ac.uk.
authors.forename: John P
authors.identifier: http://orcid.org/0000-0003-1589-7984
authors.initials: JP
authors.lastname: O'Hara
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.|Royal Centre for Defence Medicine, Birmingham, United Kingdom.|Northumbria NHS Trust and Newcastle Trust, Newcastle, United Kingdom.
authors.forename: David R
authors.initials: DR
authors.lastname: Woods
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.|Royal Centre for Defence Medicine, Birmingham, United Kingdom.|James Cook University Hospital, Middlesborough, United Kingdom.
authors.forename: Adrian
authors.initials: A
authors.lastname: Mellor
authors.affiliation: Department of Cardiology, Poole Hospital, Poole, Dorset, United Kingdom.
authors.forename: Christopher
authors.initials: C
authors.lastname: Boos
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
authors.forename: Liam
authors.initials: L
authors.lastname: Gallagher
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
authors.forename: Costas
authors.initials: C
authors.lastname: Tsakirides
authors.affiliation: School of Social and Health Sciences, Leeds Trinity University, Leeds, United Kingdom.
authors.forename: Nicola C
authors.initials: NC
authors.lastname: Arjomandkhah
authors.affiliation: Royal Centre for Defence Medicine, Birmingham, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: Holdsworth
authors.affiliation: School of Social and Health Sciences, Leeds Trinity University, Leeds, United Kingdom.
authors.forename: Carlton B
authors.initials: CB
authors.lastname: Cooke
authors.affiliation: Scottish Universities Environmental Research Centre, Glasgow, United Kingdom.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Morrison
authors.affiliation: Scottish Universities Environmental Research Centre, Glasgow, United Kingdom.
authors.forename: Thomas
authors.initials: T
authors.lastname: Preston
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, United Kingdom.
authors.forename: Roderick Fgj
authors.initials: RF
authors.lastname: King
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000328:Adult; D000531:Altitude; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002153:Calorimetry, Indirect / Q000379:methods; D002247:Carbon Isotopes / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005527:Food, Fortified / Q000600:supply & distribution*; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D001786:Blood Glucose; D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D005632:Fructose; D006003:Glycogen; D005947:Glucose
keywords: Altitude; carbon isotope; exogenous carbohydrate oxidation; liver glycogen; muscle glycogen; plasma glucose oxidation