The results of a comprehensive investigation of the effect of a 20-minute submaximal (Z1) and exhausting (Z2) work load in a group of 8 healthy volunteers on the amino acid and nitrogen metabolism indicate that, as compared with the mild and significant increase of alanine and drop of leucine (all P < 0.05) during the minor load, after an exhausting load a significant rise and concurrent drop of isoleucine, threonine, ornithine, leucine, serine, glycine, asparagine and glutamine (P < 0.01) occurs and a slightly significant drop of methionine and citrulline, while the total amino acid level is practically unaltered. The rise of alanine suggests the existence of a glucose-alanine cycle. The drop of branched amino acids is probably due to their enhanced entry into muscles, the drop of ornithine and citrulline is most probably due to inhibition of ureogenesis in the liver due to lactate and pyruvate accumulation. Exercise caused moreover a significant rise of serum ammonia and uric acid. N-urea changed only little and on average had a declining tendency. The results support data, that intense exercise increases the demands of the human organism for high quality dietary protein intake.

Keywords: Adult; Amino Acids /metabolism/; Humans; Physical Exertion /physiology/