Increased excretion of urea and N tau -methylhistidine by rats and humans after a bout of exercise.

This study was undertaken to investigate whether an exercise bout increases muscle protein degradation and amino acid catabolism. The excretion of urea and N tau -methylhistidine before and after an exercise bout was determined for both rats and human subjects. The rats ran on a treadmill until they could no longer run. Two groups of human subjects completed strenuous exercise bouts: one group (runners) ran 10-12 miles while the other group (weight lifters) performed a standard power lift routine that lasted approximately 1 h. In rats, urea excretion was elevated for the first 12 h after the exercise bout whereas N tau -methylhistidine excretion was elevated for 48 h following exercise. The increased N tau -methylhistidine excretion after exercise supports previous reports of increased protein degradation in the perfused hindquarter and increased levels of essential amino acids in muscle, liver, and plasma of exercised rats. In human subjects, both running and weight lifting resulted in increased excretion of urea and N tau -methylhistidine. The results of the present study support the hypothesis that muscle protein breakdown and amino acid catabolism are increased by exercise.