Effect of altering substrate availability on metabolism and performance during intense exercise
Open accessAbstract
The purpose of this study was to determine the effect of altering substrate availability on metabolism and performance during intense cycling. Seven highly trained men ingested a random order of three isoenergetic meals 90 min before cycling at 80 % maximal oxygen uptake (VO 2max) for 20 min (about 310 W), followed by a 600 kJ time trial lasting about 30 min. Meals consisted of either 1·2 g saturated fat/kg body mass (BM) with 3500 U heparin intravenously (HIFAT) to elevate circulating plasma free fatty acid (FA) concentration, 2·5 g carbohydrate/kg BM (CHO) to elevate plasma glucose and insulin concentrations or 2·5 g carbohydrate+20 mg nicotinic acid/kg BM (NA) to suppress lipolysis and reduce free FA concentration. HIFAT elevated free FA concentration (HIFAT 1·3 (SEM 0·2), CHO 0·2 (sem 0·1), NA 0·1 (sem 0·1) mm; P<0·001), lowered the RER (HIFAT 0·94 (sem 0·01), CHO 0·97 (sem 0·01), NA 0·98 (sem 0·01); P<0·01) and increased the rate of fat oxidation (HIFAT 24 (sem 3), CHO 12 (sem 2), NA 8 (sem 3) μmol/kg per min; P<0·01) during the 20 min ride. Marked differences in fat availability and fuel utilisation, however, had little effect on performance in the subsequent time trial (HIFAT 320 (sem 16), CHO 324 (sem 15), NA 315 (sem 13) W). We conclude: (1) increased fat availability during intense cycling increases the rate of fat oxidation; but (2) the reduction in the rate of carbohydrate oxidation in the presence of high circulating plasma free FA is unlikely to enhance intense exercise performance lasting about 1 h; (3) substrate selection during intense (about 80 % VO 2max) exercise is dominated by carbohydrate oxidation.
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Reviews and original investigations continue to highlight the known dependence on carbohydrates that exists for athletes competing to win various endurance and team sport activities.
“Excellent reviews [42, 43] and original investigations [44–49] continue to highlight the known dependence on carbohydrates that exists for athletes competing to win various endurance and team sport activities.”
From ISSN exercise & sports nutrition review update: research & recommendations (2018) · cites this paper as [47]
The Discussion (page not provided) states that athletes exercising at intensities typical of training and competition depend on carbohydrate oxidation, and the investigation provides evidence from competitive cyclists. The paper does not examine team sports, so it does not support that part of the citing sentence. (LLM, conf=0.82)
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- Authors
- Hawley, J. A., Burke, L. M., Angus, D. J., Fallon, K. E., Martin, D. T., & Febbraio, M. A.
- Affiliations
- RMIT University (AU)
- The University of Melbourne (AU)
- Corresponding author
- Hawley, John A.
- Venue
- British Journal of Nutrition
- Publisher
- Cambridge University Press (CUP)
- Published
- 2000-12
- Volume
- 84
- Issue
- 6
- Pages
- 829-838
- ISSN
- 0007-1145 (ISSN-L)
- 1475-2662
- OpenAlex
- W2108148453
- Cited by
- 63
- References
- 42
- Citations by year
- 2026: 1 · 2025: 3 · 2024: 1 · 2022: 2 · 2021: 1 · 2020: 2 · 2019: 1 · 2018: 1 · 2016: 3 · 2015: 5 · 2014: 3 · 2013: 3 · 2012: 5
- FWCI
- 1.04
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- British Journal Of Nutrition (publishedVersion)
- PubMed (publishedVersion)
- Funders
- RMIT University
- Australian Institute of Sport
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Health Sciences › Medicine › Orthopedics and Sports Medicine › Sports Performance and Training
- Keywords
- substrate availability, free fatty acids, fat oxidation, carbohydrate oxidation, substrate selection, exercise performance, heparin, nicotinic acid, lipolysis, respiratory exchange ratio, plasma glucose, insulin, time trial
- MeSH terms
- Adult, Bicycling, Blood Glucose, Diet, Dietary Carbohydrates, Dietary Fats, Epinephrine, Physical Exertion, Fatty Acids, Nonesterified, Glycerol, Heart Rate, Humans, Insulin, Male, Niacin, Norepinephrine, Nutritional Physiological Phenomena, Oxidation-Reduction, Lactic Acid
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