Journal of Applied Physiology
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J Appl Physiol (November 16, 2001). doi:10.1152/japplphysiol.00437.2001
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Articles in PresS, published online ahead of print November 16, 2001
J Appl Physiol, 10.1152/jap.00437.2001
Submitted on May 4, 2001
Accepted on October 12, 2001

Oral 13C-glucose and endogenous energy substrate oxidation during prolonged treadmill running

Stephane Couture1, Massicotte Denis2*, Lavoie Carole3, Hillaire-Marcel Claude4, and Peronnet Francois1

1 Kinesiologie, Universite de Montreal, Montreal, Quebec, Canada
2 Kinanthropologie, Universite du Quebec a Montreal, Montreal, Quebec, Canada
3 Sciences de l'activite physique, Universite du Quebec a Trois Rivieres, Trois Rivieres, Quebec, Canada
4 Sciences de la Terre, Universite du Quebec a Montreal, Montreal, Quebec, Canada

* To whom correspondence should be addressed. E-mail: massicotte.denis{at}uqam.ca.

Six male subjects were studied during running exercise (120 min, 69% VO2 max) with ingestion of a placebo or 3.5 g/kg of 13C-glucose (~2 g/min). Indirect respiratory calorimetry corrected for urea excretion in urine and sweat, V13CO2 at the mouth, and changes in plasma glucose 13C/12C, were used in order to compute energy substrate oxidation. The oxidation rate of exogenous glucose increased from 1.02 at min 60 to 1.22 g/min at min 120 providing ~24% and ~33% of the energy yield (%En). Glucose ingestion did not modify protein oxidation which provided ~4-5%En, but significantly increased glucose oxidation by ~7%, reduced lipid oxidation by ~16%, and markedly reduced endogenous glucose oxidation (1.25 vs 2.21 g/min between min 80 and 120). The oxidation rate of glucose released from the liver (0.38 and 0.47 g/min, or 10 to 13%En at min 60 and 120, respectively), and of plasma glucose (1.30 to 1.69 g/min, or 34 and 45%En, and 50 and 75% of glucose oxidation) significantly increased from min 60 to 120, while the oxidation of muscle glycogen significantly decreased (1.28 to 0.58 g of glucose/min, or 34 and 16%En, and 50 and 25% of glucose oxidation). These results indicate that during moderate prolonged running exercise, ingestion of a very large amount of glucose significantly reduces endogenous glucose oxidation, thus sparing muscle and/or liver glycogen stores.




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