Glucose oxidation during prolonged exercise evaluated with naturally labeled [13C]glucose

Abstract

By use of naturally enriched [13C]glucose as metabolic tracer, the utilization of exogenous glucose ingested during muscular exercise was investigated. Four subjects walked on an uphill treadmill for 2 h, and three other for 4 h. The energy expenditure, close to 50% of the individual maximum Vo2,, varied from 1.9 to 2.1 liters of O2/min, while the heart rate ranged between 142 and 165 beats/mm. The subjects who were on a mixed diet and had fasted overnight, were given 100 g of naturally labeled [13C]glucose. Following this intake? the expired CO2 became rapidly enriched in carbon-13. The increase was observed as early as 15 min after the oral intake, and reached a maximum within 1–2 h, when utilization of exogenous glucose varied between 500 and 650 mg/min, representing as much as 55% of the carbohydrate metabolism and 24% of the total energy expenditure. glucose metabolism; man; mass spectrometry; stable isotopes