Clinical diagnosis of overtraining using blood tests: current knowledge

PURPOSE: Overtraining results from an imbalance between training load-induced fatigue and organism's recovery abilities. Its etiology is complex and to date there is no useful clinical diagnostic tool. The purpose of this review is to discuss the blood chemistry parameters potentially useful for diagnosing overtraining in athletes. CURRENT KNOWLEDGE AND KEY POINTS: Chronic alterations of the myocyte structure may cause high plasma concentration increases of myoglobin, troponin I and creatine kinase enzyme, resulting in chemical and/or mechanical aggression. Monitoring reactive oxygen species' activity appears to be a good tool for evaluation of the metabolic stress level experienced by skeletal muscles. In energetic metabolism, a succession of chronic glycogen depletions might change the use of amino acids and lipids, inducing transient but severe hypoglycemia during exercise. A higher oxidation of circulating glutamine might cause immunosuppression (lower reactivity to inflammations and cellular traumatisms), inhibiting alarm signals during acute training. A higher branched-chain amino acid oxidation might favor free tryptophan's entry into the cerebral area, enhancing serotonin synthesis. As a consequence, asthenia and a loss of sensitivity to muscular and tendon traumatism might appear. Exercise anemia might also be a worsening factor of the physiological situation of the tired athlete, inducing predisposition to overtraining by the lower inflammation reactivity of depleted hepatic and muscular proteins. FUTURE PROSPECTS AND PROJECTS: Early diagnosis of overtraining diagnosis may be established only from a battery of analyses, which should include the whole of the potential parameters. These remain unpredictable and do not allow systematic determination of new cases. Only a longitudinal study of the physiological situation appears to allow the necessary conditions for detecting overtraining in the early stages of its process for each subject.