Exogenous carbohydrate oxidation from drinks ingested during prolonged exercise in a cold environment in humans.
Six healthy male volunteers performed four rides to exhaustion on a cycle ergometer at approximately 80% of maximal oxygen consumption. Subjects ingested a bolus volume of fluid (7.14 ml/kg) immediately before exercise and additional fluid volumes (1.43 ml/kg) every 10 min during exercise. The fluids ingested were either a flavored water control or glucose-electrolyte beverages with glucose concentrations of 2, 6, or 12%. The beverages were labeled with [U-(13)C]glucose (99.2%: 0.05 g/l). Exercise capacity was not different (P = 0.13) between trials; median (range) exercise time was 83.52 (79.85--89.68), 103.19 (78.82--108.22), 100.37 (80.60--124.07), and 94.76 (76.78--114.25) min in the 0, 2, 6, and 12% trials, respectively. The oxidation of exogenous glucose in each 15-min period was significantly lower in the 2% trial (P = 0.02) than in the 6 and 12% trials where oxidation rates were between 0.5 and 0.7 g/min. No difference in endogenous glucose oxidation was observed between trials (P = 0.71). These findings indicate that the oxidation of exogenous glucose during exercise of this intensity and duration in a cold environment is similar to that observed in warmer conditions. Thus a low oxidation of exogenous substrate is unlikely to be a factor limiting the effectiveness of carbohydrate-electrolyte drink ingestion on exercise capacity in a cold environment.
Galloway
S D
SD
Department of Biomedical Sciences, University Medical School, Foresterhill, Aberdeen AB25 2ZD, Scotland. s.d.r.galloway@stir.ac.uk
Wootton
S A
SA
Murphy
J L
JL
Maughan
R J
RJ
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000704:Analysis of Variance; D001628:Beverages; D001786:Blood Glucose / Q000378:metabolism; D002247:Carbon Isotopes; D003080:Cold Temperature; D004040:Dietary Carbohydrates; D004573:Electrolytes; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D010101:Oxygen Consumption; D005082:Physical Exertion / Q000502:physiology*; D012016:Reference Values; D013997:Time Factors
D001786:Blood Glucose; D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D004573:Electrolytes; D007773:Lactates