In sports training man tries to broaden the boundaries of his own capacities and the physical efficiency is an informative index, which defines a set of properties of the organism and, in the first place, the efficiency of blood flow and breathing mechanisms. In the article the impact of training load on the bodies of athletes, who specialize in middle distance running is analyzed and the dynamics of special efficiency, physiological mechanisms, responsible for the quality of athletes’ endurance, is determined. The dynamics of female athletes’ special efficiency manifestation has cyclical character and depends on the hormonal status change influence on the athletes’ body during the biological cycle. Special efficiency of male athletes has tendency of gradual results growth, which is explained by the functional possibilities change, resulted by the effective influence of training loads on their body. The highest efficiency has been found in the second and fourth phases, the lowest one - in the third and especially in the first and fifth phases of MC. This is due to the increased functionality of the cardiovascular system and the effectiveness of power-ensuring in the second and fourth phases and its decrease in the first and fifth phases of MC, leading to stress of adaptation processes of women’s bodies during these phases. As for men, their dynamics of special efficiency tended to gradual increase of the results, that, we think, can be explained by the growth of functional capabilities of the cardiovascular system and the effectiveness of power-ensuring on account of effective influence of training loads upon their organism.