Physiological and psychological fatigue in extreme conditions: overtraining and elite athletes

This article will review relevant mechanisms and markers associated with overtraining syndrome (OTS), and discuss signs and symptoms, differential diagnosis, and current assessment tools for fatigue within the context of overtraining. The findings are drawn from original research and review articles referenced by PubMed and ScienceDirect databases. Sources were selected for their contributions to the current knowledge of biological, psychological, and molecular mechanisms. Data were reviewed for relevance to OTS and then evaluated against criteria that included significant OTS outcomes and findings. Information was systematically analyzed to identify patterns, dependencies, connections, and causal factors. Comparative analysis was confounded by inconsistent metrics, terminology, and variable methodology; potential biomarkers, treatment and prevention approaches, and future research directions are identified. Diagnosing OTS is difficult because underlying cause(s) are unknown; one must exclude other factors that degrade performance and mood status. Many studies are confounded by inadequate experimental designs, poor measures of performance, and different methods for characterizing OTS. OTS is complex because the demands of excessive training in combination with other biologic, psychological, and social stressors are difficult to quantify. However, changes in mood are always noted. Interrelations among dietary patterns; social, psychological and physiological profiles; and the neuroendocrine, immune, and central nervous systems are complex and not adequately elucidated.