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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% W max ) 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 -1 of glucose (enriched with 13 C glucose) and 0.6 g·min -1 of fructose (enriched with 13 C 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., (© 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

Fluid retention is a recognized feature of acute mountain sickness. However, accurate assessment of hydration, including the quantification of body water, has traditionally relied on expensive and non-portable equipment limiting its utility in the field setting. We compared the assessment of total body water (TBW) and their relationship to total body weight using two non-invasive methods using the NICas single-frequency bioimpedance analysis (SF-BIA) system and the BodyStat QuadScan 4000 multifrequency BIA system (MF-BIA). TBW measurements were performed at rest at sea level and at high altitude (HA) at 3833 m postexercise and at rest and thereafter at rest at 4450 m and 5129 m on 47 subjects. The average age was 34.5 ± 9.3 years with an age range of 21-54 years (70.2% male). There were strong correlations between TBW assessment with both methods at sea level (r = 0.90; 95% CI 0.78-0.95: P<0.0001) and at HA (r = 0.92; 0.89-0.94: P<0.0001), however, TBW readings were 0.2 l and 1.91 l lower, respectively, with the NICaS. There was a stronger correlation between TBW and body weight with the QuadScan (r = 0.91; P<0.0001) than with the NICaS (r = 0.83; P<0.0001). The overall agreement between the two TBW methods was good, but the 95% confidence intervals around these agreements were relatively wide. We conclude that there was reasonable agreement between the two methods of BIA for TBW, but this agreement was lower at HA., (© 2014 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.)