Plasma glucose kinetics during prolonged exercise in trained humans when fed carbohydrate

Area of Science:

• Exercise Physiology
• Human Metabolism
• Nutritional Science

Background:

• Endurance exercise significantly impacts glucose metabolism.
• Understanding glucose disposal during prolonged exercise is crucial for performance.
• Carbohydrate ingestion is a common strategy to fuel endurance activities.

Purpose of the Study:

• To investigate the maximal glucose disposal rate during strenuous endurance exercise.
• To determine the contribution of ingested carbohydrates to glucose utilization.
• To assess the role of glucose kinetics in limiting exercise performance.

Main Methods:

• Nine endurance-trained men performed cycle ergometry to volitional fatigue.
• A primed, continuous infusion of [6,6-2H]glucose was used to measure plasma glucose kinetics.
• Ingested [3-3H]glucose quantified the appearance of exogenous carbohydrates.

Main Results:

• Plasma glucose initially increased then stabilized during exercise.
• Glucose appearance rate (R(a)) and gut R(a) increased continuously, peaking at fatigue.
• Liver glucose output remained unchanged from resting levels.
• Glucose disposal (R(d)) rose throughout exercise, reaching 118 +/- 7 micromol. kg(-1). min(-1) at fatigue.
• Estimated exogenous glucose oxidation was 1.36 +/- 0.08 g/min at fatigue.

Conclusions:

• Glucose uptake increases progressively during prolonged, strenuous exercise with carbohydrate ingestion.
• Gut glucose absorption significantly contributes to overall glucose availability.
• Enhanced glucose disposal does not appear to be a limiting factor for endurance exercise performance under these conditions.