Purpose: to establish generalized regularities of the cumulative impact of training the formation of a "functional base" in the dynamics of body growth and development. Material & methods: 263 young athletes (79 kayakers, 88 canoeists, 96 cyclists) of different ages (12-20 years) and sports qualification were examined. The studies were conducted from 2010 to 2017. The tests were performed at rest after an overnight fast and under different modes of strenuous muscular work on a cycle ergometer, as well as in natural training conditions. A complex technique was used to determine the level of functional fitness. It included the registration of the main parameters of gas exchange, external respiration, blood, the cardiovascular system at maximum one-minute and stepwise loads, at standard load and work at a critical power level, performed on a cycle ergometer attachment to a bike or a rowing machine. Results: After 15-16 years the increase of special work capacity and efficiency of the respiratory system is accompanied by a decrease in the specific weight of development of the power of functional systems and their mobility. At the same time, a natural tendency to increase stability, economy, and degree of realization of gas transport system capacities is noted. The later the specific weight of power and mobility factors in the total efficiency of the respiratory system decreases, the greater the final level of its development in the dynamics of long-term training. The combination of high training loads, the process of enhanced body growth and development can earlier than usual realize the development potential of the respiratory system. Thus it can be argued that the way of the respiratory system adaptation of young athletes in the process of long-term training should be channeled into creating optimal conditions for stimulation of maximum functional reactions of the process of oxygen delivery to working organs. In this case, a directed deepening of the tendency to tolerate ("endure") a lack of oxygen and an excess of underoxidized metabolic products should be avoided (up to the age of 17-18 years). Oxygen debt accumulation and internal environment shifts should be used only in those working conditions and to the extent that they are an additional stimulus for maximizing functional responses. Conclusions: The degree of response sensitivity decrease reflects an increase in the potential of the respiratory system reserve capacity. The decrease in functional reactivity reflects the degree of the respiratory system potential realization. It is understood as a possibility of its efficiency further increase as a result of training at the given level of system potential. Such criteria in case of their further applied development allow approaching the quantitative estimation of such hardly quantifiable factors, as a degree of system potential realization, reserve capacities for deepening the influence of the further training on the respiratory system. Deviations from optimal training regimes (based on the notions of great plasticity of the growing body, lesser reliability of functional systems) in the presence of "sensitive" periods of development, have a great and yet insufficiently clear mechanism of negative significance for the complete realization of the respiratory system potential of the body by a mature age.