This study compared the coingestion of glucose and fructose on exogenous and endogenous substrate oxidation during prolonged exercise at terrestrial high altitude (HA) versus sea level, in women.
Five women completed two bouts of cycling at the same relative workload (55% Wmax) for 120 min on acute exposure to HA (3375 m) and at sea level (~113 m). In each trial, participants ingested 1.2 g·min−1 of glucose (enriched with 13C glucose) and 0.6 g·min−1 of fructose (enriched with 13C fructose) 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.
The rates and absolute contribution of exogenous carbohydrate oxidation was significantly lower at HA compared with sea level (effect size [ES] > 0.99, P < 0.024), with the relative exogenous carbohydrate contribution approaching significance (32.6% ± 6.1% vs 36.0% ± 6.1%, ES = 0.56, P = 0.059) during the second hour of exercise. In comparison, no significant differences were observed between HA and sea level for the relative and absolute contributions of liver glucose (3.2% ± 1.2% vs 3.1% ± 0.8%, ES = 0.09, P = 0.635 and 5.1 ± 1.8 vs 5.4 ± 1.7 g, ES = 0.19, P = 0.217), and muscle glycogen (14.4% ± 12.2% vs 15.8% ± 9.3%, ES = 0.11, P = 0.934 and 23.1 ± 19.0 vs 28.7 ± 17.8 g, ES = 0.30, P = 0.367). Furthermore, there was no significant difference in total fat oxidation between HA and sea level (66.3 ± 21.4 vs 59.6 ± 7.7 g, ES = 0.32, P = 0.557).
In women, acute exposure to HA reduces the reliance on exogenous carbohydrate oxidation during cycling at the same relative exercise intensity.
1Research Institute for Sport, Physical Activity and Leisure, Leeds Beckett University, Leeds, UNITED KINGDOM
2Royal Centre for Defence Medicine, Birmingham, UNITED KINGDOM
3Northumbria NHS Trust and Newcastle Trust, UNITED KINGDOM
4James Cook University Hospital, Middlesborough, UNITED KINGDOM
5Department of Cardiology, Poole Hospital, Poole, Dorset, UNITED KINGDOM
6School of Social and Health Sciences, Leeds Trinity University, Leeds, UNITED KINGDOM
7Scottish Universities Environmental Research Centre, University of Glasgow, East Kilbridge, UNITED KINGDOM
Address for correspondence: John P. O’Hara, Ph.D., Research Institute for Sport, Physical Activity and Leisure, Carnegie School of Sport, Leeds Beckett University, Headingley Campus, Leeds, LS6 3QS, United Kingdom; E-mail: J.OHara@leedsbeckett.ac.uk.
Submitted for publication March 2019.
Accepted for publication June 2019.
Online date: July 17, 2019