Relevance. Early diagnosis of chronic overstress among athletes remains an important problem for coaches and specialists in the field of sports physiology and medicine. The goal is to study in an animal model the dynamics of autoimmune response to physical activity of different duration and intensity and to establish the prospects of the method of determining autoantibodies to cardiomyocyte proteins as an indicator of the morphofunctional state of the heart in the conditions of adaptation to muscle loads. Materials and Methods. The study was conducted in male white rats. Animals were subjected to 9 weeks of training simulated with treadban. The intensity of the load changed the angle of inclination and the speed of the tape. The amount of cardiospecific autoantibodies (auto-AB) to troponin I, to alpha-actin 1, to the human cardiac beta-myosin heavy chain MYH7 was determined in the blood by enzyme immunoassay. The relative heart mass was measured. Histomorphological assessment of cardiomyocyte condition was carried out. Statistical processing was carried out using the Student and Mann-Whitney criteria. Results and Discussion. Animal training was accompanied by moderate cardiac hypertrophy of pathological changes in cardiomyocytes. Heart weight increased by 6.9 %; 10.6 %; 12.9 % in the dynamics of 6-8-9 weeks of training. Concentrations of auto-AB to troponin I and to alpha-actin 1 were characterized by cyclicity, manifested by an increase in week 2 and a decrease by the 8th and 9th weeks of training. In the dynamics of 0-2-8-9 weeks of the experiment, the amount of auto-AB to troponin I was: 3.10.3; 4.20.9; 2.10.2; 2.00.04 ng/ml. For auto-AB to actin: 26.71.2; 31.31.4; 13.71.8; 12.11.6 ng/ml, respectively. The level of auto-AB to beta-myosin was manifested by a decrease in the dynamics of 0-6-9 weeks of training and amounted to: 16.30.9; 10.91.5; 8.20.8; 9.6 0.9 ng/ml. Conclusion. The results of determining cardiospecific auto-AB demonstrate a clear response of the immune system to the processes taking place in cardiomyocytes, which makes it possible to recommend further study of the method of determining auto-AB to cardiomyocyte proteins as a diagnostic test of the functional state of the heart muscle during the period of adaptation to physical activity.