An important and understudied problem is the state of health of children and adolescents who have experienced acute respiratory diseases or suffer from chronic diseases. Suffering from COVID-19 and post-COVID-19 syndrome, pneumonia are complex pathological conditions that significantly affect the functional capabilities of the child’s body and quality of life. Obesity, which is also an important medical and social problem, has no less impact on health. The purpose of the work is to summarize the data from the literature about the value of exercise tests in children with postcovid syndrome, after pneumonia of various etiologies, and obesity; modern aspects for assessing exercise tolerance. It is worth noting that nowadays screening programs for examining the health of children, aimed at prevention and early detection of pathological changes, play an important role. One of these methods of diagnosis, which makes it possible to determine and comprehensively analyze the body’s functional capabilities, is the assessment of exercise tolerance. The diagnostic value of analyzing the tolerance level lies in assessing the impact of various pathological conditions on the child’s health, and quality of life. The obtained results can be used to develop rehabilitation measures to eliminate the symptoms of acute diseases and improve the quality ofi fle. Tests with dosed physical exertion are used to assess exercise tolerance. The «gold standard» of the technique is cardiopulmonary exercise testing. However, world tolerance assessment guidelines include the use of other types of tests, such as office and field tests. The «gold standard» for assessing tolerance is the determination of the maximum oxygen consumption (VO2max), which characterizes the maximum amount of oxygen that is absorbed and used by the body during intense physical exertion involving a large possible part of the muscles. Also, during exercise tests, heart rate, blood pressure, and electrocardiogram recording are monitored, which creates significant diagnostic search opportunities for the pediatrician.