Influence of endurance training on plasma amino acid concentrations in humans at rest and after intense exercise

The influence of exercise training on plasma amino acid concentrations at rest and after exercise was examined in a highly trained group of humans and compared with the response of a control group of nontrained healthy humans. After a bout of intense exercise at the same relative work load, the trained group exhibited significantly (28%) higher plasma concentrations of alanine compared with the nontrained group (nontrained = 313.4 microM, trained = 401.3 microM). Other differences in plasma amino acid concentrations after exercise were related to initial differences present at rest before exercise. At rest, the trained group exhibited significantly higher plasma concentrations of leucine, isoleucine, and tyrosine. Post-exercise ammonia and lactate levels were not significantly different between the two groups when any pre-exercise differences were statistically accounted for. Alanine plays a central role as a primary gluconeogenic substrate and as an ammonia carrier. Therefore, in light of the results presented here, we propose that the higher alanine levels observed in the endurance-trained athletes after exercise may play a physiologically relevant role in accommodation to the metabolic demands of exercise.