The changes in selected muscle and blood metabolites - blood catecholamines, cyclic AMP, glucagon, growth hormone, insulin, and C-peptide--were measured in five male long-distance runners after moderate 90 min (4.3 min/km) and intense 45 min (3.3 min/km) of continuous running exercises. After the 45-min exercise, the mean concentrations of blood lactate and glucose were 2.8 and 8.8 mmol/l, respectively, and the muscle glycogen concentration had decreased by 31%. No changes could be found after the 90 min of running. The increase in blood glycerol concentration was greater after the 45-min exercise (5.8-fold) than after the 90-min exercise (3.9-fold), although the serum free fatty acid concentration increased significantly only during the 90-min exercise (1.6-fold). Plasma noradrenaline increases were 2.7-fold and 7.9-fold during the 90- and 45-min exercises, respectively, whereas the plasma adrenaline concentration was significantly elevated only after the 45-min exercise (4.7-fold). The respective changes of plasma cyclic AMP were 2.5- and 2.7-fold, and the increase in the concentration of plasma growth hormone was 5.8-fold after the 45-min exercise. The plasma insulin level decreased during the 90-min exercise, but was elevated after the 45-min exercise. The increase was greater than could be expected on the basis of the plasma C-peptide concentration. It is concluded that the hormonal and metabolic changes during submaximal long-term exercises are highly dependent on the intensity of exercise, even when the intensity of exercise is below the level of the anaerobic threshold.(ABSTRACT TRUNCATED AT 250 WORDS)