Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 Sep 15;10(9):e0138376.
doi: 10.1371/journal.pone.0138376. eCollection 2015.

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

Free PMC article

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

Francisco Areces et al. PLoS One. .
Free PMC article


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and after the race, a countermovement jump and a maximal isometric force test were performed, and blood samples were withdrawn to measure serum free amino acids concentrations, and serum creatine kinase levels as a blood marker of muscle damage.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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Fig 1
Fig 1. A) Relationship between race time and sector times (swimming, cycling and running) and post-race tryptophan/BCAA ratio during a half-ironman race. B) Relationship between post-race creatine kinase concentration and changes of BCAA concentration during a half-ironman race (as a change from pre-exercise values).
Note: A) The correlation of total race time (r = -0.05; P = 0.80), swimming time (r = -0.05; P = 0.80), cycling time (r = 0.08; P = 0.70) and running time (r = -0.21; P = 0.30) with post-race tryptophan/BCAA ratio were not statistically significant. B) The correlation of post-race creatine kinase concentration with BCAA change during the race (r = -0.02; P = 0.92) was not statistically significant.

Similar articles

See all similar articles

Cited by 9 articles

See all "Cited by" articles


    1. Millet GP, Bentley DJ, Vleck VE (2007) The relationships between science and sport: application in triathlon. Int J Sports Physiol Perform 2: 315–322. - PubMed
    1. Del Coso J, Gonzalez C, Abian-Vicen J, Salinero Martin JJ, Soriano L, Areces F, et al. (2014) Relationship between physiological parameters and performance during a half-ironman triathlon in the heat. J Sports Sci 32: 1680–1687. 10.1080/02640414.2014.915425 - DOI - PubMed
    1. Jeukendrup AE (2011) Nutrition for endurance sports: marathon, triathlon, and road cycling. J Sports Sci 29 Suppl 1: S91–99. 10.1080/02640414.2011.610348 - DOI - PubMed
    1. Garcia-Manso JM, Rodriguez-Ruiz D, Rodriguez-Matoso D, de Saa Y, Sarmiento S, Quiroga M (2011) Assessment of muscle fatigue after an ultra-endurance triathlon using tensiomyography (TMG). J Sports Sci 29: 619–625. 10.1080/02640414.2010.548822 - DOI - PubMed
    1. Del Coso J, Areces F, Salinero JJ, Gonzalez-Millan C, Abian-Vicen J, Soriano L, et al. (2014) Compression stockings do not improve muscular performance during a half-ironman triathlon race. Eur J Appl Physiol 114: 587–595. 10.1007/s00421-013-2789-2 - DOI - PubMed

Grant support

These authors have no support or funding to report.