Аim. The article deals with the study of the functional abilities of the main body systems in children, adolescents, and young males during their adaptation to physical load in sports swimming. Materials and methods. We examined male swimmers aged 9–18 years. The study consisted of 2 stages: the study of physical development, aerobic capacities, and non-specific resistance (9–18 years, n = 603); the study of adaptive reactions of the cardiovascular and respiratory systems (9–10, 11–13, and 14–16 years, n = 75). The following methods were used: anthropometry, dynamometry, ergometry, the analysis of leukocyte count, lactate analysis, rheography, spiro- and pneumotachometry, gasometry, statistical data processing, and a functional stress test. Results. We justified physiologically the potential abilities of children, adolescents, and young males practicing sports swimming to tolerate physical load of various intensity and duration. It was established that, in swimmers at the stage of performance enhancement, aerobic potential was formed in close cooperation with growth processes. At the age of 9–13, aerobic capacities are formed in a closer correlation with anthropometric data, while at the age of 14–18 – with functional and homeostatic parameters. Adaptive reactions of the body at the age of 9–13 are characterized by the imperfection of the regulatory mechanisms responsible for metabolic, hemodynamic, and ventilatory functions. This results in the increase of lactate to the values significantly exceeding the anaerobic threshold and the formation of the resistive type of hemodynamic and ventilatory reactions. At the age of 14–16, there is an increase in the adaptive capacities of the oxygen-providing systems responsible for high-intensity loads. Conclusion. Potential abilities in children and adolescents at the threshold values are decreased. This is because aerobic reserves are determined by the growth, homeostatic reactions are atypical, and ventilatory reactions are inefficient. In young males, there is an increase in the functional abilities of the oxygen-providing systems, which forms the efficient types of adaptive reactions to high-intensity loads.