Cited by 180Muscle metabolism and nutritionCardiovascular and exercise physiologySports Performance and Training

The regulation of carbohydrate and fat metabolism during and after exercise

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Holloszy, John O·1998·Frontiers in bioscience

Abstract

The rate of carbohydrate utilization during prolonged, strenuous exercise is closely geared to the energy needs of the working muscles. In contrast, fat utilization during exercise is not tightly regulated, as there are no mechanisms for closely matching availability and metabolism of fatty acids to the rate of energy expenditure. As a result, the rate of fat oxidation during exercise is determined by the availability of fatty acids and the rate of carbohydrate utilization. Blood glucose and muscle glycogen are essential for prolonged strenuous exercise, and exhaustion can result either from development of hypoglycemia or depletion of muscle glycogen. Both absolute and relative (i.e. % of maximal O2 uptake) exercise intensities play important roles in the regulation of substrate metabolism. The absolute work rate determines the total quantity of fuel required, while relative exercise intensity plays a major role in determining the proportions of carbohydrate and fat oxidized by the working muscles. As relative exercise intensity is increased, there is a decrease in the proportion of the energy requirement derived from fat oxidation and an increase in that provided by carbohydrate oxidation. During moderately strenuous exercise of an intensity that can be maintained for 90 minutes or longer ( approximately 55-75% of VO2max), there is a progressive decline in the proportion of energy derived from muscle glycogen and a progressive increase in plasma fatty acid oxidation. The adaptations induced by endurance exercise training result in a marked sparing of carbohydrate during exercise, with an increased proportion of the energy being provided by fat oxidation. The mechanisms by which training decreases utilization of blood glucose are not well understood. However, the slower rate of glycogenolysis can be explained on the basis of lower concentrations of inorganic phosphate (Pi) in trained, as compared to untrained, muscles during exercise of the same intensity. The lower Pi level is a consequence of the increase in muscle mitochondria induced by endurance exercise training. A large increase in muscle glycogen concentration, far above the level found in the well-fed sedentary state, occurs in response to carbohydrate feeding following glycogen depleting exercise. It was recently found that this muscle "glycogen supercompensation" is markedly enhanced by endurance exercise training that induces an increase in the GLUT4 isoform of the glucose transporter in skeletal muscle.

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  • There is no evidence of a mechanism to control the availability-utilisation cycle of FA to the energetic requirements of the working muscle.

    “there is no evidence of such a mechanism to control the availability–utilisation cycle of FA to the energetic requirements of the working muscle [147].”

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  1. Galbo, H. Exercise physiology: Humoral function. Sport Science Review 1, 65-93 (1992)

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Authors
Holloszy, J. O.
Affiliations
Washington University in St. Louis (US)
Corresponding author
Holloszy, John O
Venue
Frontiers in bioscience
Publisher
IMR Press
Published
1998
Volume
3
Issue
4
Pages
d1011-1027
ISSN
  • 1093-4715 (ISSN-L)
  • 1093-9946
OpenAlex
W3023039152
Cited by
180
References
157
Citations by year
2026: 2 · 2025: 3 · 2024: 4 · 2023: 4 · 2022: 10 · 2021: 4 · 2020: 6 · 2019: 5 · 2018: 9 · 2017: 6 · 2016: 7 · 2015: 10 · 2014: 6 · 2013: 9 · 2012: 6
FWCI
0.35
Type
journal article
Language
en
Open access
Locations
  • Frontiers in bioscience (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • National Institutes of Health (AG00425, AG00078)
  • National Institute on Aging (AG00425, AG 00078)
  • National Institute of Diabetes and Digestive and Kidney Diseases (DK-18986, R01DK018986)
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
exercise metabolism, carbohydrate oxidation, fat oxidation, muscle glycogen, blood glucose, endurance training, glycogen supercompensation, GLUT4, inorganic phosphate, glycogenolysis, relative exercise intensity, hypoglycemia, fatty acid availability
MeSH terms
Animals, Blood Glucose, Fatty Acids, Humans, Physical Conditioning, Animal, Exercise, Muscle, Skeletal, Carbohydrate Metabolism, Rats

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