Prognostic Potential of Time Series Markers in Cardiac Rhythmogram in Stress Testing

The analysis of individual physical exercise (PE) tolerance is related to the variability of time series (TS) in the cardiorhythmogram (CRG). Mathematical simulation (MSim) is one of the most detailed methods for such studies. We investigated the CRG variability in stress testing using mathematical simulation of its time series in order to determine the prognostic markers of PE tolerance. We examined a mixed sample (MS) of apparently healthy subjects aged 18–22 years (n = 68), which was divided into two equal groups (n = 34): athlete (1) and nonathlete (2) subjects. We performed maximal bicycle exercise testing according to an individual protocol. We applied S to the derived CRG TS. The markers of MSim for CRG TS of the early adaptation period (EAP) were matched (Spearman) with individual load and recovery values. Then we performed intergroup comparison (Mann–Whitney). It was found that the EAP CRG variability has some specific traits of the entire loading period and is connected with the individual PE tolerance. The markers of MSim for CRG TS reflect the specific traits of the entire time series and can be used to study variability and relations with other adaptation mechanisms. The minute models of EAP allowed us to reveal its critical stages: maximal variability (1–2 min) and stability (3 min); maximal variability velocity (1 min), significant velocity reduction (2 min), and minimal velocity (3 min). The last (third) minute of EAP in the mixed sample and in group 2 reflects the limit of the individual load tolerance with the highest accuracy. Homogeneous groups significantly differ in the maximal level and chronotropic parameters of PE tolerance, start time and the velocity of changes in CRG TS. At the same time, the markers of MSim for CRG TS for the mixed sample and the nonathlete group reflect the individual PE tolerance with the same accuracy as the average and maximal HR values determined for the entire loading period. For atheletes, these markers determine maximum tolerance with lower accuracy but reflect the quality of PE tolerance. The markers of MSim for the EAP reflecting the features of chronotropic adaptation can be used for screening in a mixed population; for the investigation and prediction of tolerance development, the training level, for control of PE mastering, for prevention of overload and overtraining in the athlete group; and for the evaluation of the health status and adaptation disorders (PE tolerance) in the nonathlete group.