[To the question of the heart rate fluctuations during submaximal workload]

The effect of oscillatory decrease in the heart rate and hemoglobin oxygen saturation (SaO2) during the submaximal workload (bicycle ergometry test) was demonstrated in high-performance athletes and volunteers practicing healthy life style. The obtained parameters (heart rate, SaO2, amplitude of oscillation, and recovery time) were analyzed taking into account modern notions about the mechanisms of pO2 maintenance during activation of aerobic metabolism in high-resistance organisms under extreme conditions. It is concluded that optimal functioning of cardio-respiratory system can be achieved only when its labile oscillatory parameters are synchronized at the various levels of functional hierarchy, which are maintained by the higher intensity ofredox reactions, improved utilization of oxidative destruction products, more intensive fluctuations of endogenous oxygen, and fine regulation of hemoproteins' role in the free radical reactions. This, in turn, promotes long-term adaptive activation reaction at the higher levels of reactivity. Further studies of the described oscillations could facilitate their use as the new functional diagnostic criteria for the estimation of reactivity and adaptive reserve mechanisms in sports and preventive medicine.