Background: The aim of this study was to compare chosen parameters and coefficients characterizing the action of the cardiovascular system and the respiratory system at a low level of a cycloergometric exercise in young boys practicing handball and their untrained peers. In the present study we searched for an answer to questions concerning the influence of physical training on children’s organism in progressive youth development. Material/Methods: The technique of parallel groups was used: the experimental one (boys training handball, n=12) and the control one (not trained boys, n=58). The developmental age of the subjects was evaluated by percentile charts. A fiveminute work on a bicycle ergometer was used to observe reaction of the organism to submaximal exercise below AT. During the test the parameters characterizing the respiratory and cardiovascular systems were measured by means of a gas analyzer Oxycon Pro Jaeger (Viasys) and Breath by Breath program. Results: We noted adapting changes in the circulatory system in young handball players. The group practicing handball showed a higher value of O2·HR-1 (p≤0.05) in comparison with the untrained boys. Oxygen deficit was higher in the trained group, but there were no statistically significant differences between the trained and untrained boys. Conclusions: Training during the biological progressive development causes adaptive changes in the cardiovascular system in the light of an increase in pulse oxygen (O2·HR-1) in submaximal work. Handball training during the biological progressive development causes an increase in oxygen deficit (Def. O2).