The development of occupational fatigue is one of the main reasons for the increased risk of accidents and injuries in the workplace. The state of fatigue negatively affects the health of employees and the quality of their professional activities. As for the problem of studying professional fatigue, there are different approaches to the definition of this concept and the choice of assessment methods. The study aims to analyze the features of the study of occupational fatigue in the labor physiology. In order to analyzed the main approaches of professional fatigue, we have studied domestic and foreign literary sources describing both early and modern works on this topic. The complexity of assessing professional fatigue determines the need for an integrated approach to the selection of methods from the field of physiology, psychophysiology and psychology, a combination of objective and subjective methods. It is important to take into account the limitations of these methods, which may associate with a controversial interpretation of the data, the peculiarities of the production environment, the requirements of the profession and occupational safety, so the question of choosing universal methods remains relevant and requires further study.