Fate of ¹⁴C Glucose Ingested During Prolonged Exercise*

Abstract

Six well-trained subjects cycled (50% V̇O₂max) for 180 min on two separate occasions. After 120 min, the subjects ingested 400 ml of either a 139 mM or a 589 mM glucose solution, then continued to cycle for another 60 min. Glucose-U-¹⁴C (1.85 × 10³ kBq) was added to each drink. Venous blood samples were assayed for lactic acid, FFA, glucose, and glucose-¹⁴C activity. Expired ¹⁴CO₂, urine-¹⁴C, and sweat ¹⁴C activity were also determined. By the end of exercise, the accumulated ¹⁴C recovered as ¹⁴CO₂ was less than 10% of the dose. ¹⁴C activity in sweat and urine could account for less than 2% of the total ingested. Though little of the labeled glucose present in these drinks was used oxidatively, the 589 mM solution provided blood glucose in significantly greater amounts than did the less concentrated solution. Most of the ingested glucose seemed to remain in compartments within an unoxidized glucose pool.

Key Words

carbohydrate metabolism - fluid ingestion - ergometer cycling