Changes in serum amino acid concentrations during prolonged endurance running

Eight endurance trained distance runners (5 male and 3 female) ran on a treadmill at 60% of their VO2max for 3 h. Blood samples (about 12 ml) were taken immediately prior to the exercise, and thereafter every 30 min during and at the end of exercise. Urinary urea excretion was determined for the day of exercise, and for a control day a week after the exercise. Blood samples were analyzed for glucose, free fatty acids, urea and free amino acids concentrations. As the exercise was continued, there was a gradual decrease in the concentrations in serum of alanine and proline such that the concentrations of both the amino acids were significantly less at the end of exercise than the resting values (p < 0.01). These changes appeared to be highly correlated (r = 0.981, p < 0.05). The serum glucose concentration increased significantly (p < 0.05) after 30 min of exercise, remained significantly elevated until 150 min of exercise and then decreased to reach the resting value at the completion of the exercise. Serum free fatty acid (FFA) concentration was significantly higher at the end of exercise compared to the resting value. The increase in serum FFA concentration and the decreases in the concentrations in serum of alanine and proline were also found to be highly correlated (alanine versus FFA: r = -0.986, p < 0.05; proline versus FFA: r = -0.961, p < 0.05). The total urinary urea excretion (332 +/- 43 mmol versus 424 +/- 46 mmol) and urine volume (978 +/- 187 ml versus 1,480 +/- 245 ml) were less on the day fo exercise than on the control day. The decrease in urine volume was found to be significant (p < 0.05).