Effects of military training on plasma amino acid concentrations and their associations with overreaching

Abstract

Amino acids are thought to have a key role in the processes contributing to overreaching development through their metabolic properties and neuronal functions. In the present study, the effects of 10-week military training on the concentrations of 19 amino acids were investigated. Plasma amino acid concentrations were measured at rest from 53 healthy male conscripts on weeks 1, 4, 7, and 9 of their military service. Conscripts were classified as overreached and non-overreached. Overreaching classification was based on fulfilling at least three of five criteria: greater than 5% decrease in maximal oxygen uptake, increased rating perceived exertion (RPE), and decreased lactate-RPE ratio in submaximal marching test, admitting feeling overloaded and both increased scores in fatigue and decreased scores in vigor in the Profile of Mood States Adolescents. Eight conscripts (15%) were classified as overreached; their glutamine–glutamate ratio and alanine and arginine levels were significantly lower (P < 0.05) and glutamate concentration significantly higher (P < 0.05) in comparison to their non-overreached counterparts. The levels of arginine increased (P < 0.05) and tryptophan (P < 0.001) decreased in both groups throughout the study. The tyrosine concentration increased in non-overreached but, in contrast, remained at the same level in overreached individuals (P < 0.05). The results suggest that alterations in the levels of three metabolically important amino acids, alanine, glutamate and arginine, and the possibly neuroactive tyrosine and tryptophan might explain some of the physical and psychological symptoms of overreaching. The present study also confirms the potential use of glutamine–glutamate ratio as a tool for detecting overreaching.