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.

Impact statement

The diagnosis of overtraining syndrome and overreaching poses a great challenge. Military training aims at improving the physical performance of the conscripts, but an excessive training load could also lead to overreaching. This study of Finnish conscripts provides new insights into the pathophysiology of overreaching and overtraining through amino acids concentrations. In addition to confirming the possible use of plasma glutamine/glutamate concentration to indicate and predict overreaching, we made a novel finding, i.e. low alanine and arginine concentrations might have a role in performance decrement and fatigue related to overreaching. Moreover, this study is the first to show the possible association between amino acids with putative neuronal properties and overreaching. Thus, the present findings might help to detect and prevent overreaching and offer a reliable diagnostic approach. In order to avoid overreaching, military training should be planned more periodically and individually, especially during the first four weeks of military service.