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

Abstract

Couture, Sté phane, Denis Massicotte, Carole Lavoie, Claude Hillaire-Marcel, and Franç ois Pé ronnet. Oral [ 13 C]glucose and endogenous energy substrate oxidation during prolonged treadmill running. J Appl Physiol 92: 1255-1260, 2002. First published November 16, 2001 10.1152/japplphysiol.00437.2001.-Six male subjects were studied during running exercise (120 min, 69% maximal oxygen consumption) with ingestion of a placebo or 3.5 g/kg of [ 13 C]glucose (ϳ2 g/min). Indirect respiratory calorimetry corrected for urea excretion in urine and sweat, production of 13 CO2 at the mouth, and changes in plasma glucose 13 C/ 12 C were used to compute energy substrate oxidation. The oxidation rate of exogenous glucose increased from 1.02 at minute 60 to 1.22 g/min at minute 120 providing ϳ24 and 33% of the energy yield (%En). Glucose ingestion did not modify protein oxidation, which provided ϳ4-5%En, but significantly increased glucose oxidation by ϳ7%, reduced lipid oxidation by ϳ16%, and markedly reduced endogenous glucose oxidation (1.25 vs. 2.21 g/min between minutes 80 and 120, respectively). The oxidation rate of glucose released from the liver (0.38 and 0.47 g/min, or 10-13%En at minutes 60 and 120, respectively), and of plasma glucose (1.30-1.69 g/min, or 34 and 45%En and 50 and 75% of glucose oxidation) significantly increased from minutes 60 to 120, whereas 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. exogenous glucose; stable isotopes; liver glucose production; muscle glycogen utilization; insulin; blood glucose THERE APPEARS TO BE NO detailed description of energy substrate fluxes, and particularly of plasma glucose kinetics, during prolonged running, except for the study by Hall et al. (11), which has only been presented as a preliminary report. Similarly, most of the studies concerning exogenous carbohydrate oxidation during exercise have been conducted on cycle ergometer. In these studies, the oxidation rate of exogenous carbohydrates has been shown to increase with workload (19,27,29) and with the amount ingested (1, 14, 36). At high absolute and relative workloads and for large amounts of carbohydrates ingested, the oxidation rate of exogenous glucose plateaus around 1.0 g/min, providing ϳ25% of the energy yield (13,14,26,36). When running exercise was used, the workload was low [40% maximal oxygen consumption (V O 2 max )] (22) or the amount of glucose ingested was small (0.4-0.8 g/min) (27, 28). Accordingly, the oxidation rate of exogenous glucose remained in the lower range of values reported (0.3-0.7 g/min). In the study by Derman et al. (10), exogenous glucose oxidation was compared in response to running and cycling exercise at a high workload (3.6 l O 2 /min; 80% V O 2 max ) with ingesti...

Metabolic response to prolonged cycling with 13C-glucose ingestion following downhill running

“…The oxidation rates of exogenous glucose, glucose released from the liver, plasma glucose, and glucose released from muscle glycogen, all of which were well within the range of values reported in studies from various laboratories (Couture et al 2002;Hawley et al 1992;Jeukendrup and Jentjens 2000;Pe´ronnet et al 1998), were not significantly modified 2 days following eccentric exercise. These results seem to be at odds with consistent data showing that DOMS is associated with a reduction in muscle glycogen repletion and content (Asp et al 1995aCostill et al 1990;Doyle et al 1993;Widrick et al 1992).…”

“…Carbohydrate and lipid oxidation were computed from indirect respiratory calorimetry corrected for protein oxidation. For this purpose, V _ O 2 and carbon dioxide production (V _ CO 2 ) were measured using open circuit spirometry (5-min collection period), and urea production was estimated over the exercise period as previously described (Couture et al 2002;M'Kaouar et al 2004). Briefly, urea excretion over the 120 min of exercise was estimated from its concentration in urine and sweat (Brisson et al 1991), and from urine and sweat loss.…”

Gender difference in the metabolic response to prolonged exercise with [13C]glucose ingestion

“…[g (40 min) )1 ] 12.5 (2. the oxidation of exogenous carbohydrates levels off at or around 1 g min )1 , and can contribute up to $30% to the energy yield (Couture et al 2002;Hawley et al 1992;Jeukendrup and Jentjens 2000). Data from the present experiment with ingestion of 1.8 g min )1 glucose are well in line with these consistent results.…”

Effects of ingesting [13C]glucose early or late into cold exposure on substrate utilization

“…In both experimental conditions, this fuel source contributed Ͻ15% to the total thermogenic rate by the final 30 min of cold exposure compared with the ϳ25% observed in a previous study (1). Glycogen sparing during exercise has been attributed to increased plasma glucose and insulin concentrations, combining with muscle contractions to stimulate insulinand muscle contraction-induced muscle glucose uptake (5,32). Consequently, this resulted in increased plasma glucose oxidation and an increase in its relative contribution to total energy yield, thus preserving muscle glycogen utilization.…”