Alterations in amino acid concentrations in the plasma and muscle in human subjects during 24 h of simulated adventure racing

Eur J Appl Physiol. 2012 Oct;112(10):3679-88. doi: 10.1007/s00421-012-2350-8. Epub 2012 Feb 18.


This investigation was designed to evaluate changes in plasma and muscle levels of free amino acids during an ultra-endurance exercise and following recovery. Nine male ultra-endurance trained athletes participated in a 24-h standardized endurance trial with controlled energy intake. The participants performed 12 sessions of running, kayaking and cycling (4 × each discipline). Blood samples were collected before, during and after exercise, as well as after 28 h of recovery. Muscle biopsies were taken before the test and after exercise, as well as after 28 h of recovery. During the 24-h exercise, plasma levels of branched-chain (BCAA), essential amino acids (EAA) and glutamine fell 13, 14 and 19% (P < 0.05), respectively, whereas their concentrations in muscle were unaltered. Simultaneously, tyrosine and phenylalanine levels rose 38 and 50% (P < 0.05) in the plasma and 66 and 46% (P < 0.05) in muscle, respectively. After the 24-h exercise, plasma levels of BCAA were positively correlated with muscle levels of glycogen (r (2) = 0.73, P < 0.05), as was the combined concentrations of muscle tyrosine and phenylalanine with plasma creatine kinase (R (2) = 0.55, P < 0.05). Following 28-h of recovery, plasma and muscle levels of amino acids had either returned to their initial levels or were elevated. In conclusion, ultra-endurance exercise caused significant changes elevations in plasma and muscle levels of tyrosine and phenylalanine, which suggest an increase in net muscle protein breakdown during exercise. There was a reduction in plasma concentrations of EAA and glutamine during exercise, whereas no changes were detected in their muscle concentration after exercise.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amino Acids / blood
  • Amino Acids / metabolism*
  • Exercise / physiology*
  • Glycogen / metabolism
  • Humans
  • Male
  • Muscle, Skeletal / metabolism*
  • Phenylalanine / blood
  • Running / physiology*
  • Tyrosine / blood


  • Amino Acids
  • Tyrosine
  • Phenylalanine
  • Glycogen