Relevance. Fatigue, both intellectual and physical, reduces the efficiency of daily activities and quality of life, in addition, fatigue is one of the factors contributing to the development of various pathological conditions, such as cardiovascular disease and others. Therefore, it is important to understand the mechanisms underlying the development of fatigue, which will improve prevention and development. Objective: to analyze the physiological and biochemical mechanisms underlying the development of fatigue. Methods. Analysis of scientific publications of the international scientific database PubMed by keywords. The following research methods were used in writing the paper: systematization of material, analysis and generalization. Results. In this article we discussed the physiological and biochemical mechanisms of fatigue. The correlation between fatigue and the general mental condition, physiological, biochemical processes, activity of neurotransmitters, intellectual and physical activity, food has been defined. The central and peripheral mechanisms of fatigue were considered. Central fatigue is divided into spinal and supraspinal and involves the neuromuscular junction. Peripheral fatigue occurs at the level of the muscles and mainly involves muscle bioenergetics or an excitation-contraction coupling. Currently fatigue is considered as a general reaction to stress that lasts for a period of time, taken in an account the cumulative effects of days, weeks or months, and the effects of sleep disorders are also very important, because the effects of fatigue are closely linked to sleep deprivation. Therefore, the time required for recovery depends on the severity of fatigue. There are currently many research methods, such as electromyography, transcranial magnetic stimulation, magnetic resonance imaging, and spectroscopy, which are useful in undestending the physiological correlates of fatigue. In turn, psychological, behavioral or physical triggers can have a beneficial effect against the development of acute fatigue and improve performance, as well as provide a better understanding of the function of neurotransmitters, physiological and biochemical processes important in the development of body fatigue in general.

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Psychoemotional stress that develops in dynamics of studying in university is a common factor of development of the vast group of neurogenic diseases.The objective of the research was to study the intersystem relations (integration) which are the base of development of organism's resistance to the effects of stress factors, i.e. the development of adaptive syndrome.The object of the research was a group of 256 medical students of 1–3 years which were examined in conditions of educational process. The peculiarities of intersystem integration of cardiorespiratory system based on coupling index (CI), and integrational brain activity based on intellectual workability in conditions of correction test (2 minutes of test, total percentage of completed work, number of mistakes) were studied.The research of complex of psychophysiological indicators in the dynamics of studying revealed the formation of chronic emotional stress in medical students, the severity of which depends on the individual characteristics of the psychophysiological status of students.Formation of adaptation to the educational stress has the stage character (3stages) – the initial period is accompanied by activation of non‐specific adaptive mechanisms in almost all students (1st stage). From the 2nd year, only in 40% of the students an adequate adaptation to the training load was formed – intellectual performance increases, with the background of rationalization of its vegetative support. Sustainable intersystem relationship that reveals increasing the body's integrity (2nd stage) is formed.In second group of students (43%) non‐specific adaptive mechanisms (1st stage) on the 2nd year of study goes into a stage of specific adaptation (2nd stage), but the severity of changes in psychophysiological indexes is strongly pronounced. On the 3rd year of study it leads to the depletion of adaptive capabilities (3rd stage).In 17% of students it was seen that the stage of activation of non‐specific adaptive mechanisms rapidly changed by their depletion, that is accompanied by decrease of intersystem integration and intellectual workability. This is the evidence of prevalence of disintegrational processes in the organism.Based on results of the research, a conclusion can be made that the formation of adaptive optimum to psychoemotional stress occurs only in 40% of students. The majority (60%) of students show either the initially insufficient adaptive capabilities, or their excessive intensity, that naturally leads to psychological and vegetative disorders in the organism.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.