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Fuel Use during Exercise at Altitude in Women with Glucose–Fructose Ingestion

O’HARA, JOHN P.1; DUCKWORTH, LAUREN1; BLACK, ALISTAIR1; WOODS, DAVID R.1,2,3; MELLOR, ADRIAN1,2,4; BOOS, CHRISTOPHER1,5; GALLAGHER, LIAM1; TSAKIRIDES, COSTAS1; ARJOMANDKHAH, NICOLA C.6; MORRISON, DOUGLAS J.7; PRESTON, THOMAS7; KING, RODERICK F. G. J.1

Medicine & Science in Sports & Exercise: December 2019 - Volume 51 - Issue 12 - p 2586–2594
doi: 10.1249/MSS.0000000000002072
APPLIED SCIENCES
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Purpose 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.

Method 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.

Results 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).

Conclusions 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

© 2019 American College of Sports Medicine