Restriction of physical activity causes exaggerated hyperinsulinemia and hyperglycemia following an oral glucose load. It is attributed to decreased sensitivity to insulin and decreased GLUT-4 transporter content in skeletal muscles. On the other hand, both endurance and strength training enhance whole body insulin sensitivity. Apart from increased insulin action in skeletal muscles, muscle hypertrophy is considered as the mechanism responsible for the training effect. Our previous study showed, that after three days of bed rest the plasma insulin response to a glucose load markedly increases both in untrained and in endurance-trained subjects; but the blood glucose (BG) response was less affected in athletes. The present investigation was designed to compare an effect of three day bed rest on BG and plasma insulin responses to oral glucose in untrained subjects, and in endurance or strength trained athletes. There are reports that the sympathetic nervous system activity is inhibited by bed-rest. Activation of this system after carbohydrate ingestion is considered an important mechanism contributing to dissipation of excess energy and prevention of postprandial fall in blood pressure. Thus, the second purpose of the present investigation was to find out whether short-term bed rest modifies changes in plasma catecholamines, heart rate and blood pressure following glucose ingestion.