Regulation of fatty acid oxidation in untrained vs. trained men during exercise

Labros S. Sidossis, Robert R. Wolfe, Andrew R. Coggan

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


We have recently shown that increased carbohydrate flux decreases fat oxidation during exercise by inhibition of fatty acid entry into the mitochondria. Because endurance training reduces the rate of carbohydrate flux during exercise, we hypothesized that training increases fat oxidation by relieving this inhibition. To test this hypothesis, five sedentary and five endurance-trained men exercised on a cycle ergometer at an oxygen consumption (V̇O2) of ~2.0 l/min, representing 80 and 40% peak V̇O2, respectively. [1-13C]oleate and [1-14C]octanoate, long- and medium-chain fatty acids, respectively, were infused for the duration of the studies. Carbohydrate oxidation was significantly higher in the sedentary group (196 ± 9 vs. 102 ±17 μmol · kg-1 · min-1, p < 0.05). Oleate oxidation was higher in the trained group (3.8 ± 0.6 vs. 1.9 ± 0.3 μmol · kg-1 · min-1, P < 0.05), whereas octanoate oxidation was not different between the two groups. The percentage of oleate that was taken up by tissues and oxidized was higher in the trained group (76 ± 7 vs. 58 ± 3%, P < 0.05). However, the percentage of octanoate taken up and oxidized was not different (82 ± 3 vs. 85 ± 4%, not significant). Because octanoate, unlike oleate, can freely diffuse across the mitochondrial membrane, the present results suggest that the difference in fatty acid oxidation between trained and untrained individuals may be due to enhanced fatty acid entry into the mitochondria.

Original languageEnglish (US)
Pages (from-to)E510-E515
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number3 37-3
StatePublished - Mar 1998


  • Carnitine palmitoyltransferase
  • Endurance training
  • Malonyl-coenzyme A
  • Medium- chain fatty acids
  • Mitochondria
  • Muscle

ASJC Scopus subject areas

  • General Medicine


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