Background and objectives: Physical load causes structural changes in the heart that vary depending on the type of training and may affect the function of the heart. Aim of the study: To determine, using the applied co-integration method on algebraic data, the impact of sprinting and of endurance adaptation on the dynamic interactions of cardiovascular functional indices while participants were performing under an increasing workload, up to their inability to continue. Materials and Methods: Healthy athletes were chosen to take part in this study and were separated into two groups: Sprinters (n = 11) and endurance athletes (n = 13). The bicycle ergometric method of incremental increase in a provocative workload (graded stress) was used. The heart rate, stroke volume, and cardiac output were determined using the tetrapolar rheography method. Results: Individuals who are adapted to endurance while carrying physical loads, in contrast to well adapted sprinters, are characterized with a lower rate of changing the pace of interactions between stroke volume and cardiac output while performing at an increasing workload up to their inability to continue. Also, endurance athletes displayed a long and relatively stable phase as well as a greater decrease of interaction between indices at the end of the workload. At the beginning of the exercise, the interaction between the stroke volume and the cardiac output was reduced. However, as the physical load continued, this interaction became significantly stronger. The comparison of the stroke volume and the cardiac output’s dynamic interaction revealed that the endurance group had a greater working capacity. Conclusions: Typical dynamics of interactions during the testing with an increasing physical load can be differentiated into separate phases: The decrease of interaction at the onset of the load, the increase during the continuation of an increased workload, and the decrease at the last stages of the load.

BACKGROUND: Physiology and sport science are interested in the link between the development of fatigue and exercise performance. This study tests the hypothesis that the inter-dynamics of changes in the ratio between the RR and JT intervals of ECG could be informative for defining the state of fatigue during exercising. METHODS: We used two studies to simulate various functional states and to identify the peculiarities of this interaction, and what could be useful for the precise evaluation of the functional state. Seventeen athletes participated in the first study and 12 in the second study. A bicycle ergometer test using a 12-lead ECG was recorded for later analysis. RESULTS: The first study showed that when the load was higher the difference between JT and RR intervals was also higher (P<0.05). The JT and RR did not intersect at the start of the test or throughout the test. At recovery velocity adaptation does not return to baseline value (P<0.05). The second study revealed that after a 50W, 100W and 150W workload, the RR interval outran the recovery of JT the interval, but after 200W the recovery of the JT interval was statistically higher than the recovery of the RR interval (P<0.05). After 50W, 100W and 150W, the workload at the recovery index velocity of adaption was negative compared to baseline values (P<0.05), but after 200W these values became positive (P<0.05). CONCLUSIONS: The study confirmed the hypothesis that the accumulated fatigue, caused by exercising can be evaluated by the analysis the dynamics of JT and RR intervals during the fast recovery phase.