Serum urea and amino nitrogen changes with exercise duration.

In eight groups of healthy male athlets, aged 19-44 years, serum urea, alpha-amino nitrogen and free tyrosine were determined before and after physical exercise of different duration. Exercise was competitional running, skiing, march or bicycle ergometer work, its duration between 15 and 765 min. The results were compared with previous data from this laboratory and those of other authors. After about 60-70 min of exertion, there is a significant fall in serum amino nitrogen and a rise in urea and free tyrosine; the magnitude of these changes correlated well to the duration of exercise. Likewise, there is a significant correlation between increase in serum urea and decrease in amino nitrogen. The observed changes strongly suggest an increased breakdown of nitrogen-containing compounds during prolonged exercise.