Submitted on September 7, 2004
Accepted on November 29, 2005
Exogenous carbohydrate oxidation during ultra-endurance exercise
Asker E. Jeukendrup1*, Luke Moseley1, Gareth I. Mainwaring1, Spencer Samuels1, Samuel Perry1, and Christopher H. Mann1
1 Human Performance Laboratory, School of Sport & Exercise Sciences, The University of Birmingham, Birmingham, United Kingdom
* To whom correspondence should be addressed. E-mail: a.e.jeukendrup{at}bham.ac.uk.
The purposes of this study were: 1) to obtain a measure of exogenous carbohydrate (CHOEXO) oxidation during five hours of exercise, 2) to compare CHOEXO following the ingestion of a glucose solution (GLU) or a glucose + fructose solution (2:1 ratio, GLU+FRU) during ultraendurance exercise. Eight well-trained subjects exercised 3 times for 5 h at 58%VO2max) whilst ingesting either GLU or GLU+FRU (both delivering 1.5 g/min carbohydrate) or water. The carbohydrates used had a naturally high 13C enrichment and 5 subjects received a primed continuous intravenous [6,6 2H2max] glucose infusion. CHOEXO rates following the ingestion of GLU levelled off after 120 min and peaked at 1.24 ± 0.04 g/min. The ingestion of GLU+FRU resulted in a significantly higher peak rate of CHOEXO (1.40 ± 0.08 g/min), a faster rate of increase in CHOEXO and an increase in the percentage of CHOEXO oxidised (65 to 77%). However, Ra and Rd glucose continued to increase during exercise with no differences between trials. These data suggest an important role for gluconeogenesis during the later stages of exercise. Following the ingestion of GLU+FRU cadence (rpm) was maintained, the perception of stomach fullness was reduced relative to GLU. The ingestion of glucose and fructose together increases CHOEXO compared to the ingestion of glucose alone, potentially through the oxidation of CHOEXO in the liver or through the conversion to, and oxidation of, lactate.
