Changes in Serum Free Amino Acids and Muscle Fatigue Experienced during a Half-Ironman Triathlon

The aim of this study was to investigate the relationship between changes in serum free amino acids, muscle fatigue and exercise-induced muscle damage during a half-ironman triathlon. Twenty-six experienced triathletes (age = 37.0 +/- 6.8 yr; experience = 7.4 +/- 3.0 yr) competed in a real half-ironman triathlon in which sector times and total race time were measured by means of chip timing. Before and after the race, a countermovement jump and a maximal isometric force test were performed, and blood samples were withdrawn to measure serum free amino acids concentrations, and serum creatine kinase levels as a blood marker of muscle damage. Total race time was 320 +/- 37 min and jump height (-16.3 +/- 15.2%, P < 0.001) and isometric force (-14.9 +/- 9.8%; P = 0.007) were significantly reduced after the race in all participants. After the race, the serum concentration of creatine kinase increased by 368 +/- 187% (P < 0.001). In contrast, the serum concentrations of essential (-27.1 +/- 13.0%; P < 0.001) and non-essential amino acids (-24.4 +/- 13.1%; P < 0.001) were significantly reduced after the race. The tryptophan/ BCAA ratio increased by 42.7 +/- 12.7% after the race. Pre-to-post changes in serum free amino acids did not correlate with muscle performance variables or post-race creatine kinase concentration. In summary, during a half-ironman triathlon, serum amino acids concentrations were reduced by >20%. However, neither the changes in serum free amino acids nor the tryptophan/ BCAA ratio were related muscle fatigue or muscle damage during the race.